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-rw-r--r--src/basic/tmpfile-util.c472
1 files changed, 472 insertions, 0 deletions
diff --git a/src/basic/tmpfile-util.c b/src/basic/tmpfile-util.c
new file mode 100644
index 0000000..e77ca94
--- /dev/null
+++ b/src/basic/tmpfile-util.c
@@ -0,0 +1,472 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <sys/mman.h>
+
+#include "alloc-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "hexdecoct.h"
+#include "macro.h"
+#include "memfd-util.h"
+#include "missing_fcntl.h"
+#include "missing_syscall.h"
+#include "path-util.h"
+#include "process-util.h"
+#include "random-util.h"
+#include "stat-util.h"
+#include "stdio-util.h"
+#include "string-util.h"
+#include "sync-util.h"
+#include "tmpfile-util.h"
+#include "umask-util.h"
+
+static int fopen_temporary_internal(int dir_fd, const char *path, FILE **ret_file) {
+ _cleanup_fclose_ FILE *f = NULL;
+ _cleanup_close_ int fd = -EBADF;
+ int r;
+
+ assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+ assert(path);
+
+ fd = openat(dir_fd, path, O_CLOEXEC|O_NOCTTY|O_RDWR|O_CREAT|O_EXCL, 0600);
+ if (fd < 0)
+ return -errno;
+
+ /* This assumes that returned FILE object is short-lived and used within the same single-threaded
+ * context and never shared externally, hence locking is not necessary. */
+
+ r = take_fdopen_unlocked(&fd, "w", &f);
+ if (r < 0) {
+ (void) unlinkat(dir_fd, path, 0);
+ return r;
+ }
+
+ if (ret_file)
+ *ret_file = TAKE_PTR(f);
+
+ return 0;
+}
+
+int fopen_temporary_at(int dir_fd, const char *path, FILE **ret_file, char **ret_path) {
+ _cleanup_free_ char *t = NULL;
+ int r;
+
+ assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+ assert(path);
+
+ r = tempfn_random(path, NULL, &t);
+ if (r < 0)
+ return r;
+
+ r = fopen_temporary_internal(dir_fd, t, ret_file);
+ if (r < 0)
+ return r;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(t);
+
+ return 0;
+}
+
+int fopen_temporary_child_at(int dir_fd, const char *path, FILE **ret_file, char **ret_path) {
+ _cleanup_free_ char *t = NULL;
+ int r;
+
+ assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+
+ if (!path) {
+ r = tmp_dir(&path);
+ if (r < 0)
+ return r;
+ }
+
+ r = tempfn_random_child(path, NULL, &t);
+ if (r < 0)
+ return r;
+
+ r = fopen_temporary_internal(dir_fd, t, ret_file);
+ if (r < 0)
+ return r;
+
+ if (ret_path)
+ *ret_path = TAKE_PTR(t);
+
+ return 0;
+}
+
+/* This is much like mkostemp() but is subject to umask(). */
+int mkostemp_safe(char *pattern) {
+ assert(pattern);
+ BLOCK_WITH_UMASK(0077);
+ return RET_NERRNO(mkostemp(pattern, O_CLOEXEC));
+}
+
+int fmkostemp_safe(char *pattern, const char *mode, FILE **ret_f) {
+ _cleanup_close_ int fd = -EBADF;
+ FILE *f;
+
+ fd = mkostemp_safe(pattern);
+ if (fd < 0)
+ return fd;
+
+ f = take_fdopen(&fd, mode);
+ if (!f)
+ return -errno;
+
+ *ret_f = f;
+ return 0;
+}
+
+static int tempfn_build(const char *p, const char *pre, const char *post, bool child, char **ret) {
+ _cleanup_free_ char *d = NULL, *fn = NULL, *nf = NULL, *result = NULL;
+ size_t len_pre, len_post, len_add;
+ int r;
+
+ assert(p);
+ assert(ret);
+
+ /*
+ * Turns this:
+ * /foo/bar/waldo
+ *
+ * Into this :
+ * /foo/bar/waldo/.#<pre><post> (child == true)
+ * /foo/bar/.#<pre>waldo<post> (child == false)
+ */
+
+ if (pre && strchr(pre, '/'))
+ return -EINVAL;
+
+ if (post && strchr(post, '/'))
+ return -EINVAL;
+
+ len_pre = strlen_ptr(pre);
+ len_post = strlen_ptr(post);
+ /* NAME_MAX is counted *without* the trailing NUL byte. */
+ if (len_pre > NAME_MAX - STRLEN(".#") ||
+ len_post > NAME_MAX - STRLEN(".#") - len_pre)
+ return -EINVAL;
+
+ len_add = len_pre + len_post + STRLEN(".#");
+
+ if (child) {
+ d = strdup(p);
+ if (!d)
+ return -ENOMEM;
+ } else {
+ r = path_extract_directory(p, &d);
+ if (r < 0 && r != -EDESTADDRREQ) /* EDESTADDRREQ → No directory specified, just a filename */
+ return r;
+
+ r = path_extract_filename(p, &fn);
+ if (r < 0)
+ return r;
+
+ if (strlen(fn) > NAME_MAX - len_add)
+ /* We cannot simply prepend and append strings to the filename. Let's truncate the filename. */
+ fn[NAME_MAX - len_add] = '\0';
+ }
+
+ nf = strjoin(".#", strempty(pre), strempty(fn), strempty(post));
+ if (!nf)
+ return -ENOMEM;
+
+ if (d) {
+ if (!path_extend(&d, nf))
+ return -ENOMEM;
+
+ result = path_simplify(TAKE_PTR(d));
+ } else
+ result = TAKE_PTR(nf);
+
+ if (!path_is_valid(result)) /* New path is not valid? (Maybe because too long?) Refuse. */
+ return -EINVAL;
+
+ *ret = TAKE_PTR(result);
+ return 0;
+}
+
+int tempfn_xxxxxx(const char *p, const char *extra, char **ret) {
+ /*
+ * Turns this:
+ * /foo/bar/waldo
+ *
+ * Into this:
+ * /foo/bar/.#<extra>waldoXXXXXX
+ */
+
+ return tempfn_build(p, extra, "XXXXXX", /* child = */ false, ret);
+}
+
+int tempfn_random(const char *p, const char *extra, char **ret) {
+ _cleanup_free_ char *s = NULL;
+
+ assert(p);
+ assert(ret);
+
+ /*
+ * Turns this:
+ * /foo/bar/waldo
+ *
+ * Into this:
+ * /foo/bar/.#<extra>waldobaa2a261115984a9
+ */
+
+ if (asprintf(&s, "%016" PRIx64, random_u64()) < 0)
+ return -ENOMEM;
+
+ return tempfn_build(p, extra, s, /* child = */ false, ret);
+}
+
+int tempfn_random_child(const char *p, const char *extra, char **ret) {
+ _cleanup_free_ char *s = NULL;
+ int r;
+
+ assert(ret);
+
+ /* Turns this:
+ * /foo/bar/waldo
+ * Into this:
+ * /foo/bar/waldo/.#<extra>3c2b6219aa75d7d0
+ */
+
+ if (!p) {
+ r = tmp_dir(&p);
+ if (r < 0)
+ return r;
+ }
+
+ if (asprintf(&s, "%016" PRIx64, random_u64()) < 0)
+ return -ENOMEM;
+
+ return tempfn_build(p, extra, s, /* child = */ true, ret);
+}
+
+int open_tmpfile_unlinkable(const char *directory, int flags) {
+ char *p;
+ int fd, r;
+
+ if (!directory) {
+ r = tmp_dir(&directory);
+ if (r < 0)
+ return r;
+ } else if (isempty(directory))
+ return -EINVAL;
+
+ /* Returns an unlinked temporary file that cannot be linked into the file system anymore */
+
+ /* Try O_TMPFILE first, if it is supported */
+ fd = open(directory, flags|O_TMPFILE|O_EXCL, S_IRUSR|S_IWUSR);
+ if (fd >= 0)
+ return fd;
+
+ /* Fall back to unguessable name + unlinking */
+ p = strjoina(directory, "/systemd-tmp-XXXXXX");
+
+ fd = mkostemp_safe(p);
+ if (fd < 0)
+ return fd;
+
+ (void) unlink(p);
+
+ return fd;
+}
+
+int open_tmpfile_linkable_at(int dir_fd, const char *target, int flags, char **ret_path) {
+ _cleanup_free_ char *tmp = NULL;
+ int r, fd;
+
+ assert(target);
+ assert(ret_path);
+
+ /* Don't allow O_EXCL, as that has a special meaning for O_TMPFILE */
+ assert((flags & O_EXCL) == 0);
+
+ /* Creates a temporary file, that shall be renamed to "target" later. If possible, this uses O_TMPFILE – in
+ * which case "ret_path" will be returned as NULL. If not possible the temporary path name used is returned in
+ * "ret_path". Use link_tmpfile() below to rename the result after writing the file in full. */
+
+ fd = open_parent_at(dir_fd, target, O_TMPFILE|flags, 0640);
+ if (fd >= 0) {
+ *ret_path = NULL;
+ return fd;
+ }
+
+ log_debug_errno(fd, "Failed to use O_TMPFILE for %s: %m", target);
+
+ r = tempfn_random(target, NULL, &tmp);
+ if (r < 0)
+ return r;
+
+ fd = openat(dir_fd, tmp, O_CREAT|O_EXCL|O_NOFOLLOW|O_NOCTTY|flags, 0640);
+ if (fd < 0)
+ return -errno;
+
+ *ret_path = TAKE_PTR(tmp);
+
+ return fd;
+}
+
+int fopen_tmpfile_linkable(const char *target, int flags, char **ret_path, FILE **ret_file) {
+ _cleanup_free_ char *path = NULL;
+ _cleanup_fclose_ FILE *f = NULL;
+ _cleanup_close_ int fd = -EBADF;
+
+ assert(target);
+ assert(ret_file);
+ assert(ret_path);
+
+ fd = open_tmpfile_linkable(target, flags, &path);
+ if (fd < 0)
+ return fd;
+
+ f = take_fdopen(&fd, "w");
+ if (!f)
+ return -ENOMEM;
+
+ *ret_path = TAKE_PTR(path);
+ *ret_file = TAKE_PTR(f);
+ return 0;
+}
+
+static int link_fd(int fd, int newdirfd, const char *newpath) {
+ int r;
+
+ assert(fd >= 0);
+ assert(newdirfd >= 0 || newdirfd == AT_FDCWD);
+ assert(newpath);
+
+ /* Try symlinking via /proc/fd/ first. */
+ r = RET_NERRNO(linkat(AT_FDCWD, FORMAT_PROC_FD_PATH(fd), newdirfd, newpath, AT_SYMLINK_FOLLOW));
+ if (r != -ENOENT)
+ return r;
+
+ /* Fall back to symlinking via AT_EMPTY_PATH as fallback (this requires CAP_DAC_READ_SEARCH and a
+ * more recent kernel, but does not require /proc/ mounted) */
+ if (proc_mounted() != 0)
+ return r;
+
+ return RET_NERRNO(linkat(fd, "", newdirfd, newpath, AT_EMPTY_PATH));
+}
+
+int link_tmpfile_at(int fd, int dir_fd, const char *path, const char *target, LinkTmpfileFlags flags) {
+ _cleanup_free_ char *tmp = NULL;
+ int r;
+
+ assert(fd >= 0);
+ assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+ assert(target);
+
+ /* Moves a temporary file created with open_tmpfile() above into its final place. If "path" is NULL
+ * an fd created with O_TMPFILE is assumed, and linkat() is used. Otherwise it is assumed O_TMPFILE
+ * is not supported on the directory, and renameat2() is used instead. */
+
+ if (FLAGS_SET(flags, LINK_TMPFILE_SYNC) && fsync(fd) < 0)
+ return -errno;
+
+ if (path) {
+ if (FLAGS_SET(flags, LINK_TMPFILE_REPLACE))
+ r = RET_NERRNO(renameat(dir_fd, path, dir_fd, target));
+ else
+ r = rename_noreplace(dir_fd, path, dir_fd, target);
+ if (r < 0)
+ return r;
+ } else {
+
+ r = link_fd(fd, dir_fd, target);
+ if (r != -EEXIST || !FLAGS_SET(flags, LINK_TMPFILE_REPLACE))
+ return r;
+
+ /* So the target already exists and we were asked to replace it. That sucks a bit, since the kernel's
+ * linkat() logic does not allow that. We work-around this by linking the file to a random name
+ * first, and then renaming that to the final name. This reintroduces the race O_TMPFILE kinda is
+ * trying to fix, but at least the vulnerability window (i.e. where the file is linked into the file
+ * system under a temporary name) is very short. */
+
+ r = tempfn_random(target, NULL, &tmp);
+ if (r < 0)
+ return r;
+
+ if (link_fd(fd, dir_fd, tmp) < 0)
+ return -EEXIST; /* propagate original error */
+
+ r = RET_NERRNO(renameat(dir_fd, tmp, dir_fd, target));
+ if (r < 0) {
+ (void) unlinkat(dir_fd, tmp, 0);
+ return r;
+ }
+ }
+
+ if (FLAGS_SET(flags, LINK_TMPFILE_SYNC)) {
+ r = fsync_full(fd);
+ if (r < 0)
+ return r;
+ }
+
+ return 0;
+}
+
+int flink_tmpfile(FILE *f, const char *path, const char *target, LinkTmpfileFlags flags) {
+ int fd, r;
+
+ assert(f);
+ assert(target);
+
+ fd = fileno(f);
+ if (fd < 0) /* Not all FILE* objects encapsulate fds */
+ return -EBADF;
+
+ r = fflush_and_check(f);
+ if (r < 0)
+ return r;
+
+ return link_tmpfile(fd, path, target, flags);
+}
+
+int mkdtemp_malloc(const char *template, char **ret) {
+ _cleanup_free_ char *p = NULL;
+ int r;
+
+ assert(ret);
+
+ if (template)
+ p = strdup(template);
+ else {
+ const char *tmp;
+
+ r = tmp_dir(&tmp);
+ if (r < 0)
+ return r;
+
+ p = path_join(tmp, "XXXXXX");
+ }
+ if (!p)
+ return -ENOMEM;
+
+ if (!mkdtemp(p))
+ return -errno;
+
+ *ret = TAKE_PTR(p);
+ return 0;
+}
+
+int mkdtemp_open(const char *template, int flags, char **ret) {
+ _cleanup_free_ char *p = NULL;
+ int fd, r;
+
+ r = mkdtemp_malloc(template, &p);
+ if (r < 0)
+ return r;
+
+ fd = RET_NERRNO(open(p, O_DIRECTORY|O_CLOEXEC|flags));
+ if (fd < 0) {
+ (void) rmdir(p);
+ return fd;
+ }
+
+ if (ret)
+ *ret = TAKE_PTR(p);
+
+ return fd;
+}
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