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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-10 20:49:52 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-10 20:49:52 +0000
commit55944e5e40b1be2afc4855d8d2baf4b73d1876b5 (patch)
tree33f869f55a1b149e9b7c2b7e201867ca5dd52992 /src/basic/chase.c
parentInitial commit. (diff)
downloadsystemd-55944e5e40b1be2afc4855d8d2baf4b73d1876b5.tar.xz
systemd-55944e5e40b1be2afc4855d8d2baf4b73d1876b5.zip
Adding upstream version 255.4.upstream/255.4
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/basic/chase.c')
-rw-r--r--src/basic/chase.c1156
1 files changed, 1156 insertions, 0 deletions
diff --git a/src/basic/chase.c b/src/basic/chase.c
new file mode 100644
index 0000000..26bc2d6
--- /dev/null
+++ b/src/basic/chase.c
@@ -0,0 +1,1156 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <linux/magic.h>
+
+#include "alloc-util.h"
+#include "chase.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "glyph-util.h"
+#include "log.h"
+#include "path-util.h"
+#include "string-util.h"
+#include "user-util.h"
+
+bool unsafe_transition(const struct stat *a, const struct stat *b) {
+ /* Returns true if the transition from a to b is safe, i.e. that we never transition from unprivileged to
+ * privileged files or directories. Why bother? So that unprivileged code can't symlink to privileged files
+ * making us believe we read something safe even though it isn't safe in the specific context we open it in. */
+
+ if (a->st_uid == 0) /* Transitioning from privileged to unprivileged is always fine */
+ return false;
+
+ return a->st_uid != b->st_uid; /* Otherwise we need to stay within the same UID */
+}
+
+static int log_unsafe_transition(int a, int b, const char *path, ChaseFlags flags) {
+ _cleanup_free_ char *n1 = NULL, *n2 = NULL, *user_a = NULL, *user_b = NULL;
+ struct stat st;
+
+ if (!FLAGS_SET(flags, CHASE_WARN))
+ return -ENOLINK;
+
+ (void) fd_get_path(a, &n1);
+ (void) fd_get_path(b, &n2);
+
+ if (fstat(a, &st) == 0)
+ user_a = uid_to_name(st.st_uid);
+ if (fstat(b, &st) == 0)
+ user_b = uid_to_name(st.st_uid);
+
+ return log_warning_errno(SYNTHETIC_ERRNO(ENOLINK),
+ "Detected unsafe path transition %s (owned by %s) %s %s (owned by %s) during canonicalization of %s.",
+ strna(n1), strna(user_a), special_glyph(SPECIAL_GLYPH_ARROW_RIGHT), strna(n2), strna(user_b), path);
+}
+
+static int log_autofs_mount_point(int fd, const char *path, ChaseFlags flags) {
+ _cleanup_free_ char *n1 = NULL;
+
+ if (!FLAGS_SET(flags, CHASE_WARN))
+ return -EREMOTE;
+
+ (void) fd_get_path(fd, &n1);
+
+ return log_warning_errno(SYNTHETIC_ERRNO(EREMOTE),
+ "Detected autofs mount point %s during canonicalization of %s.",
+ strna(n1), path);
+}
+
+static int log_prohibited_symlink(int fd, ChaseFlags flags) {
+ _cleanup_free_ char *n1 = NULL;
+
+ assert(fd >= 0);
+
+ if (!FLAGS_SET(flags, CHASE_WARN))
+ return -EREMCHG;
+
+ (void) fd_get_path(fd, &n1);
+
+ return log_warning_errno(SYNTHETIC_ERRNO(EREMCHG),
+ "Detected symlink where not symlink is allowed at %s, refusing.",
+ strna(n1));
+}
+
+static int chaseat_needs_absolute(int dir_fd, const char *path) {
+ if (dir_fd < 0)
+ return path_is_absolute(path);
+
+ return dir_fd_is_root(dir_fd);
+}
+
+int chaseat(int dir_fd, const char *path, ChaseFlags flags, char **ret_path, int *ret_fd) {
+ _cleanup_free_ char *buffer = NULL, *done = NULL;
+ _cleanup_close_ int fd = -EBADF, root_fd = -EBADF;
+ unsigned max_follow = CHASE_MAX; /* how many symlinks to follow before giving up and returning ELOOP */
+ bool exists = true, append_trail_slash = false;
+ struct stat st; /* stat obtained from fd */
+ const char *todo;
+ int r;
+
+ assert(!FLAGS_SET(flags, CHASE_PREFIX_ROOT));
+ assert(!FLAGS_SET(flags, CHASE_STEP|CHASE_EXTRACT_FILENAME));
+ assert(!FLAGS_SET(flags, CHASE_TRAIL_SLASH|CHASE_EXTRACT_FILENAME));
+ assert(!FLAGS_SET(flags, CHASE_MKDIR_0755) || (flags & (CHASE_NONEXISTENT | CHASE_PARENT)) != 0);
+ assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+
+ /* Either the file may be missing, or we return an fd to the final object, but both make no sense */
+ if (FLAGS_SET(flags, CHASE_NONEXISTENT))
+ assert(!ret_fd);
+
+ if (FLAGS_SET(flags, CHASE_STEP))
+ assert(!ret_fd);
+
+ if (isempty(path))
+ path = ".";
+
+ /* This function resolves symlinks of the path relative to the given directory file descriptor. If
+ * CHASE_AT_RESOLVE_IN_ROOT is specified and a directory file descriptor is provided, symlinks
+ * are resolved relative to the given directory file descriptor. Otherwise, they are resolved
+ * relative to the root directory of the host.
+ *
+ * Note that when a positive directory file descriptor is provided and CHASE_AT_RESOLVE_IN_ROOT is
+ * specified and we find an absolute symlink, it is resolved relative to given directory file
+ * descriptor and not the root of the host. Also, when following relative symlinks, this functions
+ * ensures they cannot be used to "escape" the given directory file descriptor. If a positive
+ * directory file descriptor is provided, the "path" parameter is always interpreted relative to the
+ * given directory file descriptor, even if it is absolute. If the given directory file descriptor is
+ * AT_FDCWD and "path" is absolute, it is interpreted relative to the root directory of the host.
+ *
+ * When "dir_fd" points to a non-root directory and CHASE_AT_RESOLVE_IN_ROOT is set, this function
+ * always returns a relative path in "ret_path", even if "path" is an absolute path, because openat()
+ * like functions generally ignore the directory fd if they are provided with an absolute path. When
+ * CHASE_AT_RESOLVE_IN_ROOT is not set, then this returns relative path to the specified file
+ * descriptor if all resolved symlinks are relative, otherwise absolute path will be returned. When
+ * "dir_fd" is AT_FDCWD and "path" is an absolute path, we return an absolute path in "ret_path"
+ * because otherwise, if the caller passes the returned relative path to another openat() like
+ * function, it would be resolved relative to the current working directory instead of to "/".
+ *
+ * Summary about the result path:
+ * - "dir_fd" points to the root directory
+ * → result will be absolute
+ * - "dir_fd" points to a non-root directory, and CHASE_AT_RESOLVE_IN_ROOT is set
+ * → relative
+ * - "dir_fd" points to a non-root directory, and CHASE_AT_RESOLVE_IN_ROOT is not set
+ * → relative when all resolved symlinks are relative, otherwise absolute
+ * - "dir_fd" is AT_FDCWD, and "path" is absolute
+ * → absolute
+ * - "dir_fd" is AT_FDCWD, and "path" is relative
+ * → relative when all resolved symlinks are relative, otherwise absolute
+ *
+ * Algorithmically this operates on two path buffers: "done" are the components of the path we
+ * already processed and resolved symlinks, "." and ".." of. "todo" are the components of the path we
+ * still need to process. On each iteration, we move one component from "todo" to "done", processing
+ * its special meaning each time. We always keep an O_PATH fd to the component we are currently
+ * processing, thus keeping lookup races to a minimum.
+ *
+ * Suggested usage: whenever you want to canonicalize a path, use this function. Pass the absolute
+ * path you got as-is: fully qualified and relative to your host's root. Optionally, specify the
+ * "dir_fd" parameter to tell this function what to do when encountering a symlink with an absolute
+ * path as directory: resolve it relative to the given directory file descriptor.
+ *
+ * There are five ways to invoke this function:
+ *
+ * 1. Without CHASE_STEP or ret_fd: in this case the path is resolved and the normalized path is
+ * returned in `ret_path`. The return value is < 0 on error. If CHASE_NONEXISTENT is also set, 0
+ * is returned if the file doesn't exist, > 0 otherwise. If CHASE_NONEXISTENT is not set, >= 0 is
+ * returned if the destination was found, -ENOENT if it wasn't.
+ *
+ * 2. With ret_fd: in this case the destination is opened after chasing it as O_PATH and this file
+ * descriptor is returned as return value. This is useful to open files relative to some root
+ * directory. Note that the returned O_PATH file descriptors must be converted into a regular one
+ * (using fd_reopen() or such) before it can be used for reading/writing. ret_fd may not be
+ * combined with CHASE_NONEXISTENT.
+ *
+ * 3. With CHASE_STEP: in this case only a single step of the normalization is executed, i.e. only
+ * the first symlink or ".." component of the path is resolved, and the resulting path is
+ * returned. This is useful if a caller wants to trace the path through the file system verbosely.
+ * Returns < 0 on error, > 0 if the path is fully normalized, and == 0 for each normalization
+ * step. This may be combined with CHASE_NONEXISTENT, in which case 1 is returned when a component
+ * is not found.
+ *
+ * 4. With CHASE_SAFE: in this case the path must not contain unsafe transitions, i.e. transitions
+ * from unprivileged to privileged files or directories. In such cases the return value is
+ * -ENOLINK. If CHASE_WARN is also set, a warning describing the unsafe transition is emitted.
+ * CHASE_WARN cannot be used in PID 1.
+ *
+ * 5. With CHASE_NO_AUTOFS: in this case if an autofs mount point is encountered, path normalization
+ * is aborted and -EREMOTE is returned. If CHASE_WARN is also set, a warning showing the path of
+ * the mount point is emitted. CHASE_WARN cannot be used in PID 1.
+ */
+
+ if (FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT)) {
+ /* If we get AT_FDCWD or dir_fd points to "/", then we always resolve symlinks relative to
+ * the host's root. Hence, CHASE_AT_RESOLVE_IN_ROOT is meaningless. */
+
+ r = dir_fd_is_root_or_cwd(dir_fd);
+ if (r < 0)
+ return r;
+ if (r > 0)
+ flags &= ~CHASE_AT_RESOLVE_IN_ROOT;
+ }
+
+ if (!(flags &
+ (CHASE_AT_RESOLVE_IN_ROOT|CHASE_NONEXISTENT|CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_STEP|
+ CHASE_PROHIBIT_SYMLINKS|CHASE_MKDIR_0755)) &&
+ !ret_path && ret_fd) {
+
+ /* Shortcut the ret_fd case if the caller isn't interested in the actual path and has no root
+ * set and doesn't care about any of the other special features we provide either. */
+ r = openat(dir_fd, path, O_PATH|O_CLOEXEC|(FLAGS_SET(flags, CHASE_NOFOLLOW) ? O_NOFOLLOW : 0));
+ if (r < 0)
+ return -errno;
+
+ *ret_fd = r;
+ return 0;
+ }
+
+ buffer = strdup(path);
+ if (!buffer)
+ return -ENOMEM;
+
+ /* If we receive an absolute path together with AT_FDCWD, we need to return an absolute path, because
+ * a relative path would be interpreted relative to the current working directory. Also, let's make
+ * the result absolute when the file descriptor of the root directory is specified. */
+ r = chaseat_needs_absolute(dir_fd, path);
+ if (r < 0)
+ return r;
+
+ bool need_absolute = r;
+ if (need_absolute) {
+ done = strdup("/");
+ if (!done)
+ return -ENOMEM;
+ }
+
+ /* If a positive directory file descriptor is provided, always resolve the given path relative to it,
+ * regardless of whether it is absolute or not. If we get AT_FDCWD, follow regular openat()
+ * semantics, if the path is relative, resolve against the current working directory. Otherwise,
+ * resolve against root. */
+ fd = openat(dir_fd, done ?: ".", O_CLOEXEC|O_DIRECTORY|O_PATH);
+ if (fd < 0)
+ return -errno;
+
+ if (fstat(fd, &st) < 0)
+ return -errno;
+
+ /* If we get AT_FDCWD, we always resolve symlinks relative to the host's root. Only if a positive
+ * directory file descriptor is provided we will look at CHASE_AT_RESOLVE_IN_ROOT to determine
+ * whether to resolve symlinks in it or not. */
+ if (dir_fd >= 0 && FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT))
+ root_fd = openat(dir_fd, ".", O_CLOEXEC|O_DIRECTORY|O_PATH);
+ else
+ root_fd = open("/", O_CLOEXEC|O_DIRECTORY|O_PATH);
+ if (root_fd < 0)
+ return -errno;
+
+ if (FLAGS_SET(flags, CHASE_TRAIL_SLASH))
+ append_trail_slash = ENDSWITH_SET(buffer, "/", "/.");
+
+ for (todo = buffer;;) {
+ _cleanup_free_ char *first = NULL;
+ _cleanup_close_ int child = -EBADF;
+ struct stat st_child;
+ const char *e;
+
+ r = path_find_first_component(&todo, /* accept_dot_dot= */ true, &e);
+ if (r < 0)
+ return r;
+ if (r == 0) { /* We reached the end. */
+ if (append_trail_slash)
+ if (!strextend(&done, "/"))
+ return -ENOMEM;
+ break;
+ }
+
+ first = strndup(e, r);
+ if (!first)
+ return -ENOMEM;
+
+ /* Two dots? Then chop off the last bit of what we already found out. */
+ if (path_equal(first, "..")) {
+ _cleanup_free_ char *parent = NULL;
+ _cleanup_close_ int fd_parent = -EBADF;
+ struct stat st_parent;
+
+ /* If we already are at the top, then going up will not change anything. This is
+ * in-line with how the kernel handles this. */
+ if (empty_or_root(done) && FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT)) {
+ if (FLAGS_SET(flags, CHASE_STEP))
+ goto chased_one;
+ continue;
+ }
+
+ fd_parent = openat(fd, "..", O_CLOEXEC|O_NOFOLLOW|O_PATH|O_DIRECTORY);
+ if (fd_parent < 0)
+ return -errno;
+
+ if (fstat(fd_parent, &st_parent) < 0)
+ return -errno;
+
+ /* If we opened the same directory, that _may_ indicate that we're at the host root
+ * directory. Let's confirm that in more detail with dir_fd_is_root(). And if so,
+ * going up won't change anything. */
+ if (stat_inode_same(&st_parent, &st)) {
+ r = dir_fd_is_root(fd);
+ if (r < 0)
+ return r;
+ if (r > 0) {
+ if (FLAGS_SET(flags, CHASE_STEP))
+ goto chased_one;
+ continue;
+ }
+ }
+
+ r = path_extract_directory(done, &parent);
+ if (r >= 0) {
+ assert(!need_absolute || path_is_absolute(parent));
+ free_and_replace(done, parent);
+ } else if (r == -EDESTADDRREQ) {
+ /* 'done' contains filename only (i.e. no slash). */
+ assert(!need_absolute);
+ done = mfree(done);
+ } else if (r == -EADDRNOTAVAIL) {
+ /* 'done' is "/". This branch should be already handled in the above. */
+ assert(!FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT));
+ assert_not_reached();
+ } else if (r == -EINVAL) {
+ /* 'done' is an empty string, ends with '..', or an invalid path. */
+ assert(!need_absolute);
+ assert(!FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT));
+
+ if (!path_is_valid(done))
+ return -EINVAL;
+
+ /* If we're at the top of "dir_fd", start appending ".." to "done". */
+ if (!path_extend(&done, ".."))
+ return -ENOMEM;
+ } else
+ return r;
+
+ if (FLAGS_SET(flags, CHASE_STEP))
+ goto chased_one;
+
+ if (FLAGS_SET(flags, CHASE_SAFE) &&
+ unsafe_transition(&st, &st_parent))
+ return log_unsafe_transition(fd, fd_parent, path, flags);
+
+ /* If the path ends on a "..", and CHASE_PARENT is specified then our current 'fd' is
+ * the child of the returned normalized path, not the parent as requested. To correct
+ * this we have to go *two* levels up. */
+ if (FLAGS_SET(flags, CHASE_PARENT) && isempty(todo)) {
+ _cleanup_close_ int fd_grandparent = -EBADF;
+ struct stat st_grandparent;
+
+ fd_grandparent = openat(fd_parent, "..", O_CLOEXEC|O_NOFOLLOW|O_PATH|O_DIRECTORY);
+ if (fd_grandparent < 0)
+ return -errno;
+
+ if (fstat(fd_grandparent, &st_grandparent) < 0)
+ return -errno;
+
+ if (FLAGS_SET(flags, CHASE_SAFE) &&
+ unsafe_transition(&st_parent, &st_grandparent))
+ return log_unsafe_transition(fd_parent, fd_grandparent, path, flags);
+
+ st = st_grandparent;
+ close_and_replace(fd, fd_grandparent);
+ break;
+ }
+
+ /* update fd and stat */
+ st = st_parent;
+ close_and_replace(fd, fd_parent);
+ continue;
+ }
+
+ /* Otherwise let's see what this is. */
+ child = r = RET_NERRNO(openat(fd, first, O_CLOEXEC|O_NOFOLLOW|O_PATH));
+ if (r < 0) {
+ if (r != -ENOENT)
+ return r;
+
+ if (!isempty(todo) && !path_is_safe(todo))
+ return r;
+
+ if (FLAGS_SET(flags, CHASE_MKDIR_0755) && !isempty(todo)) {
+ child = xopenat(fd,
+ first,
+ O_DIRECTORY|O_CREAT|O_EXCL|O_NOFOLLOW|O_CLOEXEC,
+ /* xopen_flags = */ 0,
+ 0755);
+ if (child < 0)
+ return child;
+ } else if (FLAGS_SET(flags, CHASE_PARENT) && isempty(todo)) {
+ if (!path_extend(&done, first))
+ return -ENOMEM;
+
+ break;
+ } else if (FLAGS_SET(flags, CHASE_NONEXISTENT)) {
+ if (!path_extend(&done, first, todo))
+ return -ENOMEM;
+
+ exists = false;
+ break;
+ } else
+ return r;
+ }
+
+ if (fstat(child, &st_child) < 0)
+ return -errno;
+
+ if (FLAGS_SET(flags, CHASE_SAFE) &&
+ unsafe_transition(&st, &st_child))
+ return log_unsafe_transition(fd, child, path, flags);
+
+ if (FLAGS_SET(flags, CHASE_NO_AUTOFS) &&
+ fd_is_fs_type(child, AUTOFS_SUPER_MAGIC) > 0)
+ return log_autofs_mount_point(child, path, flags);
+
+ if (S_ISLNK(st_child.st_mode) && !(FLAGS_SET(flags, CHASE_NOFOLLOW) && isempty(todo))) {
+ _cleanup_free_ char *destination = NULL;
+
+ if (FLAGS_SET(flags, CHASE_PROHIBIT_SYMLINKS))
+ return log_prohibited_symlink(child, flags);
+
+ /* This is a symlink, in this case read the destination. But let's make sure we
+ * don't follow symlinks without bounds. */
+ if (--max_follow <= 0)
+ return -ELOOP;
+
+ r = readlinkat_malloc(fd, first, &destination);
+ if (r < 0)
+ return r;
+ if (isempty(destination))
+ return -EINVAL;
+
+ if (path_is_absolute(destination)) {
+
+ /* An absolute destination. Start the loop from the beginning, but use the
+ * root file descriptor as base. */
+
+ safe_close(fd);
+ fd = fd_reopen(root_fd, O_CLOEXEC|O_PATH|O_DIRECTORY);
+ if (fd < 0)
+ return fd;
+
+ if (fstat(fd, &st) < 0)
+ return -errno;
+
+ if (FLAGS_SET(flags, CHASE_SAFE) &&
+ unsafe_transition(&st_child, &st))
+ return log_unsafe_transition(child, fd, path, flags);
+
+ /* When CHASE_AT_RESOLVE_IN_ROOT is not set, now the chased path may be
+ * outside of the specified dir_fd. Let's make the result absolute. */
+ if (!FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT))
+ need_absolute = true;
+
+ r = free_and_strdup(&done, need_absolute ? "/" : NULL);
+ if (r < 0)
+ return r;
+ }
+
+ /* Prefix what's left to do with what we just read, and start the loop again, but
+ * remain in the current directory. */
+ if (!path_extend(&destination, todo))
+ return -ENOMEM;
+
+ free_and_replace(buffer, destination);
+ todo = buffer;
+
+ if (FLAGS_SET(flags, CHASE_STEP))
+ goto chased_one;
+
+ continue;
+ }
+
+ /* If this is not a symlink, then let's just add the name we read to what we already verified. */
+ if (!path_extend(&done, first))
+ return -ENOMEM;
+
+ if (FLAGS_SET(flags, CHASE_PARENT) && isempty(todo))
+ break;
+
+ /* And iterate again, but go one directory further down. */
+ st = st_child;
+ close_and_replace(fd, child);
+ }
+
+ if (FLAGS_SET(flags, CHASE_PARENT)) {
+ r = stat_verify_directory(&st);
+ if (r < 0)
+ return r;
+ }
+
+ if (ret_path) {
+ if (FLAGS_SET(flags, CHASE_EXTRACT_FILENAME) && done) {
+ _cleanup_free_ char *f = NULL;
+
+ r = path_extract_filename(done, &f);
+ if (r < 0 && r != -EADDRNOTAVAIL)
+ return r;
+
+ /* If we get EADDRNOTAVAIL we clear done and it will get reinitialized by the next block. */
+ free_and_replace(done, f);
+ }
+
+ if (!done) {
+ assert(!need_absolute || FLAGS_SET(flags, CHASE_EXTRACT_FILENAME));
+ done = strdup(append_trail_slash ? "./" : ".");
+ if (!done)
+ return -ENOMEM;
+ }
+
+ *ret_path = TAKE_PTR(done);
+ }
+
+ if (ret_fd) {
+ /* Return the O_PATH fd we currently are looking to the caller. It can translate it to a
+ * proper fd by opening /proc/self/fd/xyz. */
+
+ assert(fd >= 0);
+ *ret_fd = TAKE_FD(fd);
+ }
+
+ if (FLAGS_SET(flags, CHASE_STEP))
+ return 1;
+
+ return exists;
+
+chased_one:
+ if (ret_path) {
+ const char *e;
+
+ if (!done) {
+ assert(!need_absolute);
+ done = strdup(append_trail_slash ? "./" : ".");
+ if (!done)
+ return -ENOMEM;
+ }
+
+ /* todo may contain slashes at the beginning. */
+ r = path_find_first_component(&todo, /* accept_dot_dot= */ true, &e);
+ if (r < 0)
+ return r;
+ if (r == 0)
+ *ret_path = TAKE_PTR(done);
+ else {
+ char *c;
+
+ c = path_join(done, e);
+ if (!c)
+ return -ENOMEM;
+
+ *ret_path = c;
+ }
+ }
+
+ return 0;
+}
+
+static int empty_or_root_to_null(const char **path) {
+ int r;
+
+ assert(path);
+
+ /* This nullifies the input path when the path is empty or points to "/". */
+
+ if (empty_or_root(*path)) {
+ *path = NULL;
+ return 0;
+ }
+
+ r = path_is_root(*path);
+ if (r < 0)
+ return r;
+ if (r > 0)
+ *path = NULL;
+
+ return 0;
+}
+
+int chase(const char *path, const char *root, ChaseFlags flags, char **ret_path, int *ret_fd) {
+ _cleanup_free_ char *root_abs = NULL, *absolute = NULL, *p = NULL;
+ _cleanup_close_ int fd = -EBADF, pfd = -EBADF;
+ int r;
+
+ assert(path);
+
+ if (isempty(path))
+ return -EINVAL;
+
+ r = empty_or_root_to_null(&root);
+ if (r < 0)
+ return r;
+
+ /* A root directory of "/" or "" is identical to "/". */
+ if (empty_or_root(root)) {
+ root = "/";
+
+ /* When the root directory is "/", we will drop CHASE_AT_RESOLVE_IN_ROOT in chaseat(),
+ * hence below is not necessary, but let's shortcut. */
+ flags &= ~CHASE_AT_RESOLVE_IN_ROOT;
+
+ } else {
+ r = path_make_absolute_cwd(root, &root_abs);
+ if (r < 0)
+ return r;
+
+ /* Simplify the root directory, so that it has no duplicate slashes and nothing at the
+ * end. While we won't resolve the root path we still simplify it. */
+ root = path_simplify(root_abs);
+
+ assert(path_is_absolute(root));
+ assert(!empty_or_root(root));
+
+ if (FLAGS_SET(flags, CHASE_PREFIX_ROOT)) {
+ absolute = path_join(root, path);
+ if (!absolute)
+ return -ENOMEM;
+ }
+
+ flags |= CHASE_AT_RESOLVE_IN_ROOT;
+ }
+
+ if (!absolute) {
+ r = path_make_absolute_cwd(path, &absolute);
+ if (r < 0)
+ return r;
+ }
+
+ path = path_startswith(absolute, root);
+ if (!path)
+ return log_full_errno(FLAGS_SET(flags, CHASE_WARN) ? LOG_WARNING : LOG_DEBUG,
+ SYNTHETIC_ERRNO(ECHRNG),
+ "Specified path '%s' is outside of specified root directory '%s', refusing to resolve.",
+ absolute, root);
+
+ fd = open(root, O_CLOEXEC|O_DIRECTORY|O_PATH);
+ if (fd < 0)
+ return -errno;
+
+ r = chaseat(fd, path, flags & ~CHASE_PREFIX_ROOT, ret_path ? &p : NULL, ret_fd ? &pfd : NULL);
+ if (r < 0)
+ return r;
+
+ if (ret_path) {
+ if (!FLAGS_SET(flags, CHASE_EXTRACT_FILENAME)) {
+
+ /* When "root" points to the root directory, the result of chaseat() is always
+ * absolute, hence it is not necessary to prefix with the root. When "root" points to
+ * a non-root directory, the result path is always normalized and relative, hence
+ * we can simply call path_join() and not necessary to call path_simplify().
+ * Note that the result of chaseat() may start with "." (more specifically, it may be
+ * "." or "./"), and we need to drop "." in that case. */
+
+ if (empty_or_root(root))
+ assert(path_is_absolute(p));
+ else {
+ char *q;
+
+ assert(!path_is_absolute(p));
+
+ q = path_join(root, p + (*p == '.'));
+ if (!q)
+ return -ENOMEM;
+
+ free_and_replace(p, q);
+ }
+ }
+
+ *ret_path = TAKE_PTR(p);
+ }
+
+ if (ret_fd)
+ *ret_fd = TAKE_FD(pfd);
+
+ return r;
+}
+
+int chaseat_prefix_root(const char *path, const char *root, char **ret) {
+ char *q;
+ int r;
+
+ assert(path);
+ assert(ret);
+
+ /* This is mostly for prefixing the result of chaseat(). */
+
+ if (!path_is_absolute(path)) {
+ _cleanup_free_ char *root_abs = NULL;
+
+ r = empty_or_root_to_null(&root);
+ if (r < 0 && r != -ENOENT)
+ return r;
+
+ /* If the dir_fd points to the root directory, chaseat() always returns an absolute path. */
+ if (empty_or_root(root))
+ return -EINVAL;
+
+ r = path_make_absolute_cwd(root, &root_abs);
+ if (r < 0)
+ return r;
+
+ root = path_simplify(root_abs);
+
+ q = path_join(root, path + (path[0] == '.' && IN_SET(path[1], '/', '\0')));
+ } else
+ q = strdup(path);
+ if (!q)
+ return -ENOMEM;
+
+ *ret = q;
+ return 0;
+}
+
+int chase_extract_filename(const char *path, const char *root, char **ret) {
+ int r;
+
+ /* This is similar to path_extract_filename(), but takes root directory.
+ * The result should be consistent with chase() with CHASE_EXTRACT_FILENAME. */
+
+ assert(path);
+ assert(ret);
+
+ if (isempty(path))
+ return -EINVAL;
+
+ if (!path_is_absolute(path))
+ return -EINVAL;
+
+ r = empty_or_root_to_null(&root);
+ if (r < 0 && r != -ENOENT)
+ return r;
+
+ if (!empty_or_root(root)) {
+ _cleanup_free_ char *root_abs = NULL;
+
+ r = path_make_absolute_cwd(root, &root_abs);
+ if (r < 0)
+ return r;
+
+ path = path_startswith(path, root_abs);
+ if (!path)
+ return -EINVAL;
+ }
+
+ if (!isempty(path)) {
+ r = path_extract_filename(path, ret);
+ if (r != -EADDRNOTAVAIL)
+ return r;
+ }
+
+ char *fname = strdup(".");
+ if (!fname)
+ return -ENOMEM;
+
+ *ret = fname;
+ return 0;
+}
+
+int chase_and_open(const char *path, const char *root, ChaseFlags chase_flags, int open_flags, char **ret_path) {
+ _cleanup_close_ int path_fd = -EBADF;
+ _cleanup_free_ char *p = NULL, *fname = NULL;
+ mode_t mode = open_flags & O_DIRECTORY ? 0755 : 0644;
+ int r;
+
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
+
+ if (empty_or_root(root) && !ret_path &&
+ (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
+ /* Shortcut this call if none of the special features of this call are requested */
+ return xopenat(AT_FDCWD, path,
+ open_flags | (FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? O_NOFOLLOW : 0),
+ /* xopen_flags = */ 0,
+ mode);
+
+ r = chase(path, root, CHASE_PARENT|chase_flags, &p, &path_fd);
+ if (r < 0)
+ return r;
+ assert(path_fd >= 0);
+
+ if (!FLAGS_SET(chase_flags, CHASE_PARENT) &&
+ !FLAGS_SET(chase_flags, CHASE_EXTRACT_FILENAME)) {
+ r = chase_extract_filename(p, root, &fname);
+ if (r < 0)
+ return r;
+ }
+
+ r = xopenat(path_fd, strempty(fname), open_flags|O_NOFOLLOW, /* xopen_flags = */ 0, mode);
+ if (r < 0)
+ return r;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(p);
+
+ return r;
+}
+
+int chase_and_opendir(const char *path, const char *root, ChaseFlags chase_flags, char **ret_path, DIR **ret_dir) {
+ _cleanup_close_ int path_fd = -EBADF;
+ _cleanup_free_ char *p = NULL;
+ DIR *d;
+ int r;
+
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
+ assert(ret_dir);
+
+ if (empty_or_root(root) && !ret_path &&
+ (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0) {
+ /* Shortcut this call if none of the special features of this call are requested */
+ d = opendir(path);
+ if (!d)
+ return -errno;
+
+ *ret_dir = d;
+ return 0;
+ }
+
+ r = chase(path, root, chase_flags, ret_path ? &p : NULL, &path_fd);
+ if (r < 0)
+ return r;
+ assert(path_fd >= 0);
+
+ d = xopendirat(path_fd, ".", O_NOFOLLOW);
+ if (!d)
+ return -errno;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(p);
+
+ *ret_dir = d;
+ return 0;
+}
+
+int chase_and_stat(const char *path, const char *root, ChaseFlags chase_flags, char **ret_path, struct stat *ret_stat) {
+ _cleanup_close_ int path_fd = -EBADF;
+ _cleanup_free_ char *p = NULL;
+ int r;
+
+ assert(path);
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
+ assert(ret_stat);
+
+ if (empty_or_root(root) && !ret_path &&
+ (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
+ /* Shortcut this call if none of the special features of this call are requested */
+ return RET_NERRNO(fstatat(AT_FDCWD, path, ret_stat,
+ FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? AT_SYMLINK_NOFOLLOW : 0));
+
+ r = chase(path, root, chase_flags, ret_path ? &p : NULL, &path_fd);
+ if (r < 0)
+ return r;
+ assert(path_fd >= 0);
+
+ if (fstat(path_fd, ret_stat) < 0)
+ return -errno;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(p);
+
+ return 0;
+}
+
+int chase_and_access(const char *path, const char *root, ChaseFlags chase_flags, int access_mode, char **ret_path) {
+ _cleanup_close_ int path_fd = -EBADF;
+ _cleanup_free_ char *p = NULL;
+ int r;
+
+ assert(path);
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
+
+ if (empty_or_root(root) && !ret_path &&
+ (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
+ /* Shortcut this call if none of the special features of this call are requested */
+ return RET_NERRNO(faccessat(AT_FDCWD, path, access_mode,
+ FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? AT_SYMLINK_NOFOLLOW : 0));
+
+ r = chase(path, root, chase_flags, ret_path ? &p : NULL, &path_fd);
+ if (r < 0)
+ return r;
+ assert(path_fd >= 0);
+
+ r = access_fd(path_fd, access_mode);
+ if (r < 0)
+ return r;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(p);
+
+ return 0;
+}
+
+int chase_and_fopen_unlocked(
+ const char *path,
+ const char *root,
+ ChaseFlags chase_flags,
+ const char *open_flags,
+ char **ret_path,
+ FILE **ret_file) {
+
+ _cleanup_free_ char *final_path = NULL;
+ _cleanup_close_ int fd = -EBADF;
+ int mode_flags, r;
+
+ assert(path);
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP|CHASE_PARENT)));
+ assert(open_flags);
+ assert(ret_file);
+
+ mode_flags = fopen_mode_to_flags(open_flags);
+ if (mode_flags < 0)
+ return mode_flags;
+
+ fd = chase_and_open(path, root, chase_flags, mode_flags, ret_path ? &final_path : NULL);
+ if (fd < 0)
+ return fd;
+
+ r = take_fdopen_unlocked(&fd, open_flags, ret_file);
+ if (r < 0)
+ return r;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(final_path);
+
+ return 0;
+}
+
+int chase_and_unlink(const char *path, const char *root, ChaseFlags chase_flags, int unlink_flags, char **ret_path) {
+ _cleanup_free_ char *p = NULL, *fname = NULL;
+ _cleanup_close_ int fd = -EBADF;
+ int r;
+
+ assert(path);
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP|CHASE_PARENT)));
+
+ fd = chase_and_open(path, root, chase_flags|CHASE_PARENT|CHASE_NOFOLLOW, O_PATH|O_DIRECTORY|O_CLOEXEC, &p);
+ if (fd < 0)
+ return fd;
+
+ r = path_extract_filename(p, &fname);
+ if (r < 0)
+ return r;
+
+ if (unlinkat(fd, fname, unlink_flags) < 0)
+ return -errno;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(p);
+
+ return 0;
+}
+
+int chase_and_open_parent(const char *path, const char *root, ChaseFlags chase_flags, char **ret_filename) {
+ int pfd, r;
+
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
+
+ r = chase(path, root, CHASE_PARENT|CHASE_EXTRACT_FILENAME|chase_flags, ret_filename, &pfd);
+ if (r < 0)
+ return r;
+
+ return pfd;
+}
+
+int chase_and_openat(int dir_fd, const char *path, ChaseFlags chase_flags, int open_flags, char **ret_path) {
+ _cleanup_close_ int path_fd = -EBADF;
+ _cleanup_free_ char *p = NULL, *fname = NULL;
+ mode_t mode = open_flags & O_DIRECTORY ? 0755 : 0644;
+ int r;
+
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
+
+ if (dir_fd == AT_FDCWD && !ret_path &&
+ (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
+ /* Shortcut this call if none of the special features of this call are requested */
+ return xopenat(dir_fd, path,
+ open_flags | (FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? O_NOFOLLOW : 0),
+ /* xopen_flags = */ 0,
+ mode);
+
+ r = chaseat(dir_fd, path, chase_flags|CHASE_PARENT, &p, &path_fd);
+ if (r < 0)
+ return r;
+
+ if (!FLAGS_SET(chase_flags, CHASE_PARENT)) {
+ r = path_extract_filename(p, &fname);
+ if (r < 0 && r != -EADDRNOTAVAIL)
+ return r;
+ }
+
+ r = xopenat(path_fd, strempty(fname), open_flags|O_NOFOLLOW, /* xopen_flags = */ 0, mode);
+ if (r < 0)
+ return r;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(p);
+
+ return r;
+}
+
+int chase_and_opendirat(int dir_fd, const char *path, ChaseFlags chase_flags, char **ret_path, DIR **ret_dir) {
+ _cleanup_close_ int path_fd = -EBADF;
+ _cleanup_free_ char *p = NULL;
+ DIR *d;
+ int r;
+
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
+ assert(ret_dir);
+
+ if (dir_fd == AT_FDCWD && !ret_path &&
+ (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0) {
+ /* Shortcut this call if none of the special features of this call are requested */
+ d = opendir(path);
+ if (!d)
+ return -errno;
+
+ *ret_dir = d;
+ return 0;
+ }
+
+ r = chaseat(dir_fd, path, chase_flags, ret_path ? &p : NULL, &path_fd);
+ if (r < 0)
+ return r;
+ assert(path_fd >= 0);
+
+ d = xopendirat(path_fd, ".", O_NOFOLLOW);
+ if (!d)
+ return -errno;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(p);
+
+ *ret_dir = d;
+ return 0;
+}
+
+int chase_and_statat(int dir_fd, const char *path, ChaseFlags chase_flags, char **ret_path, struct stat *ret_stat) {
+ _cleanup_close_ int path_fd = -EBADF;
+ _cleanup_free_ char *p = NULL;
+ int r;
+
+ assert(path);
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
+ assert(ret_stat);
+
+ if (dir_fd == AT_FDCWD && !ret_path &&
+ (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
+ /* Shortcut this call if none of the special features of this call are requested */
+ return RET_NERRNO(fstatat(AT_FDCWD, path, ret_stat,
+ FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? AT_SYMLINK_NOFOLLOW : 0));
+
+ r = chaseat(dir_fd, path, chase_flags, ret_path ? &p : NULL, &path_fd);
+ if (r < 0)
+ return r;
+ assert(path_fd >= 0);
+
+ if (fstat(path_fd, ret_stat) < 0)
+ return -errno;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(p);
+
+ return 0;
+}
+
+int chase_and_accessat(int dir_fd, const char *path, ChaseFlags chase_flags, int access_mode, char **ret_path) {
+ _cleanup_close_ int path_fd = -EBADF;
+ _cleanup_free_ char *p = NULL;
+ int r;
+
+ assert(path);
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
+
+ if (dir_fd == AT_FDCWD && !ret_path &&
+ (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_PROHIBIT_SYMLINKS|CHASE_PARENT|CHASE_MKDIR_0755)) == 0)
+ /* Shortcut this call if none of the special features of this call are requested */
+ return RET_NERRNO(faccessat(AT_FDCWD, path, access_mode,
+ FLAGS_SET(chase_flags, CHASE_NOFOLLOW) ? AT_SYMLINK_NOFOLLOW : 0));
+
+ r = chaseat(dir_fd, path, chase_flags, ret_path ? &p : NULL, &path_fd);
+ if (r < 0)
+ return r;
+ assert(path_fd >= 0);
+
+ r = access_fd(path_fd, access_mode);
+ if (r < 0)
+ return r;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(p);
+
+ return 0;
+}
+
+int chase_and_fopenat_unlocked(
+ int dir_fd,
+ const char *path,
+ ChaseFlags chase_flags,
+ const char *open_flags,
+ char **ret_path,
+ FILE **ret_file) {
+
+ _cleanup_free_ char *final_path = NULL;
+ _cleanup_close_ int fd = -EBADF;
+ int mode_flags, r;
+
+ assert(path);
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP|CHASE_PARENT)));
+ assert(open_flags);
+ assert(ret_file);
+
+ mode_flags = fopen_mode_to_flags(open_flags);
+ if (mode_flags < 0)
+ return mode_flags;
+
+ fd = chase_and_openat(dir_fd, path, chase_flags, mode_flags, ret_path ? &final_path : NULL);
+ if (fd < 0)
+ return fd;
+
+ r = take_fdopen_unlocked(&fd, open_flags, ret_file);
+ if (r < 0)
+ return r;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(final_path);
+
+ return 0;
+}
+
+int chase_and_unlinkat(int dir_fd, const char *path, ChaseFlags chase_flags, int unlink_flags, char **ret_path) {
+ _cleanup_free_ char *p = NULL, *fname = NULL;
+ _cleanup_close_ int fd = -EBADF;
+ int r;
+
+ assert(path);
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP|CHASE_PARENT)));
+
+ fd = chase_and_openat(dir_fd, path, chase_flags|CHASE_PARENT|CHASE_NOFOLLOW, O_PATH|O_DIRECTORY|O_CLOEXEC, &p);
+ if (fd < 0)
+ return fd;
+
+ r = path_extract_filename(p, &fname);
+ if (r < 0)
+ return r;
+
+ if (unlinkat(fd, fname, unlink_flags) < 0)
+ return -errno;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(p);
+
+ return 0;
+}
+
+int chase_and_open_parent_at(int dir_fd, const char *path, ChaseFlags chase_flags, char **ret_filename) {
+ int pfd, r;
+
+ assert(!(chase_flags & (CHASE_NONEXISTENT|CHASE_STEP)));
+
+ r = chaseat(dir_fd, path, CHASE_PARENT|CHASE_EXTRACT_FILENAME|chase_flags, ret_filename, &pfd);
+ if (r < 0)
+ return r;
+
+ return pfd;
+}