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-rw-r--r--src/nspawn/nspawn-patch-uid.c477
1 files changed, 477 insertions, 0 deletions
diff --git a/src/nspawn/nspawn-patch-uid.c b/src/nspawn/nspawn-patch-uid.c
new file mode 100644
index 0000000..b8918a2
--- /dev/null
+++ b/src/nspawn/nspawn-patch-uid.c
@@ -0,0 +1,477 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <fcntl.h>
+#include <sys/statvfs.h>
+#include <sys/vfs.h>
+#include <unistd.h>
+
+#include "acl-util.h"
+#include "dirent-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "missing_magic.h"
+#include "nspawn-def.h"
+#include "nspawn-patch-uid.h"
+#include "stat-util.h"
+#include "stdio-util.h"
+#include "string-util.h"
+#include "strv.h"
+#include "user-util.h"
+
+#if HAVE_ACL
+
+static int get_acl(int fd, const char *name, acl_type_t type, acl_t *ret) {
+ acl_t acl;
+
+ assert(fd >= 0);
+ assert(ret);
+
+ if (name) {
+ _cleanup_close_ int child_fd = -EBADF;
+
+ child_fd = openat(fd, name, O_PATH|O_CLOEXEC|O_NOFOLLOW);
+ if (child_fd < 0)
+ return -errno;
+
+ acl = acl_get_file(FORMAT_PROC_FD_PATH(child_fd), type);
+ } else if (type == ACL_TYPE_ACCESS)
+ acl = acl_get_fd(fd);
+ else
+ acl = acl_get_file(FORMAT_PROC_FD_PATH(fd), type);
+ if (!acl)
+ return -errno;
+
+ *ret = acl;
+ return 0;
+}
+
+static int set_acl(int fd, const char *name, acl_type_t type, acl_t acl) {
+ int r;
+
+ assert(fd >= 0);
+ assert(acl);
+
+ if (name) {
+ _cleanup_close_ int child_fd = -EBADF;
+
+ child_fd = openat(fd, name, O_PATH|O_CLOEXEC|O_NOFOLLOW);
+ if (child_fd < 0)
+ return -errno;
+
+ r = acl_set_file(FORMAT_PROC_FD_PATH(child_fd), type, acl);
+ } else if (type == ACL_TYPE_ACCESS)
+ r = acl_set_fd(fd, acl);
+ else
+ r = acl_set_file(FORMAT_PROC_FD_PATH(fd), type, acl);
+ if (r < 0)
+ return -errno;
+
+ return 0;
+}
+
+static int shift_acl(acl_t acl, uid_t shift, acl_t *ret) {
+ _cleanup_(acl_freep) acl_t copy = NULL;
+ acl_entry_t i;
+ int r;
+
+ assert(acl);
+ assert(ret);
+
+ r = acl_get_entry(acl, ACL_FIRST_ENTRY, &i);
+ if (r < 0)
+ return -errno;
+ while (r > 0) {
+ uid_t *old_uid, new_uid;
+ bool modify = false;
+ acl_tag_t tag;
+
+ if (acl_get_tag_type(i, &tag) < 0)
+ return -errno;
+
+ if (IN_SET(tag, ACL_USER, ACL_GROUP)) {
+
+ /* We don't distinguish here between uid_t and gid_t, let's make sure the compiler checks that
+ * this is actually OK */
+ assert_cc(sizeof(uid_t) == sizeof(gid_t));
+
+ old_uid = acl_get_qualifier(i);
+ if (!old_uid)
+ return -errno;
+
+ new_uid = shift | (*old_uid & UINT32_C(0xFFFF));
+ if (!uid_is_valid(new_uid))
+ return -EINVAL;
+
+ modify = new_uid != *old_uid;
+ if (modify && !copy) {
+ int n;
+
+ /* There's no copy of the ACL yet? if so, let's create one, and start the loop from the
+ * beginning, so that we copy all entries, starting from the first, this time. */
+
+ n = acl_entries(acl);
+ if (n < 0)
+ return -errno;
+
+ copy = acl_init(n);
+ if (!copy)
+ return -errno;
+
+ /* Seek back to the beginning */
+ r = acl_get_entry(acl, ACL_FIRST_ENTRY, &i);
+ if (r < 0)
+ return -errno;
+ continue;
+ }
+ }
+
+ if (copy) {
+ acl_entry_t new_entry;
+
+ if (acl_create_entry(&copy, &new_entry) < 0)
+ return -errno;
+
+ if (acl_copy_entry(new_entry, i) < 0)
+ return -errno;
+
+ if (modify)
+ if (acl_set_qualifier(new_entry, &new_uid) < 0)
+ return -errno;
+ }
+
+ r = acl_get_entry(acl, ACL_NEXT_ENTRY, &i);
+ if (r < 0)
+ return -errno;
+ }
+
+ *ret = TAKE_PTR(copy);
+
+ return !!*ret;
+}
+
+static int patch_acls(int fd, const char *name, const struct stat *st, uid_t shift) {
+ _cleanup_(acl_freep) acl_t acl = NULL, shifted = NULL;
+ bool changed = false;
+ int r;
+
+ assert(fd >= 0);
+ assert(st);
+
+ /* ACLs are not supported on symlinks, there's no point in trying */
+ if (S_ISLNK(st->st_mode))
+ return 0;
+
+ r = get_acl(fd, name, ACL_TYPE_ACCESS, &acl);
+ if (r == -EOPNOTSUPP)
+ return 0;
+ if (r < 0)
+ return r;
+
+ r = shift_acl(acl, shift, &shifted);
+ if (r < 0)
+ return r;
+ if (r > 0) {
+ r = set_acl(fd, name, ACL_TYPE_ACCESS, shifted);
+ if (r < 0)
+ return r;
+
+ changed = true;
+ }
+
+ if (S_ISDIR(st->st_mode)) {
+ acl_free(acl);
+
+ if (shifted)
+ acl_free(shifted);
+
+ acl = shifted = NULL;
+
+ r = get_acl(fd, name, ACL_TYPE_DEFAULT, &acl);
+ if (r < 0)
+ return r;
+
+ r = shift_acl(acl, shift, &shifted);
+ if (r < 0)
+ return r;
+ if (r > 0) {
+ r = set_acl(fd, name, ACL_TYPE_DEFAULT, shifted);
+ if (r < 0)
+ return r;
+
+ changed = true;
+ }
+ }
+
+ return changed;
+}
+
+#else
+
+static int patch_acls(int fd, const char *name, const struct stat *st, uid_t shift) {
+ return 0;
+}
+
+#endif
+
+static int patch_fd(int fd, const char *name, const struct stat *st, uid_t shift) {
+ uid_t new_uid;
+ gid_t new_gid;
+ bool changed = false;
+ int r;
+
+ assert(fd >= 0);
+ assert(st);
+
+ new_uid = shift | (st->st_uid & UINT32_C(0xFFFF));
+ new_gid = (gid_t) shift | (st->st_gid & UINT32_C(0xFFFF));
+
+ if (!uid_is_valid(new_uid) || !gid_is_valid(new_gid))
+ return -EINVAL;
+
+ if (st->st_uid != new_uid || st->st_gid != new_gid) {
+ if (name)
+ r = fchownat(fd, name, new_uid, new_gid, AT_SYMLINK_NOFOLLOW);
+ else
+ r = fchown(fd, new_uid, new_gid);
+ if (r < 0)
+ return -errno;
+
+ /* The Linux kernel alters the mode in some cases of chown(). Let's undo this. */
+ if (name) {
+ if (!S_ISLNK(st->st_mode))
+ r = fchmodat(fd, name, st->st_mode, 0);
+ else /* Changing the mode of a symlink is not supported by Linux kernel. Don't bother. */
+ r = 0;
+ } else
+ r = fchmod(fd, st->st_mode);
+ if (r < 0)
+ return -errno;
+
+ changed = true;
+ }
+
+ r = patch_acls(fd, name, st, shift);
+ if (r < 0)
+ return r;
+
+ return r > 0 || changed;
+}
+
+/*
+ * Check if the filesystem is fully compatible with user namespaces or
+ * UID/GID patching. Some filesystems in this list can be fully mounted inside
+ * user namespaces, however their inodes may relate to host resources or only
+ * valid in the global user namespace, therefore no patching should be applied.
+ */
+static int is_fs_fully_userns_compatible(const struct statfs *sfs) {
+
+ assert(sfs);
+
+ return F_TYPE_EQUAL(sfs->f_type, BINFMTFS_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, CGROUP_SUPER_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, CGROUP2_SUPER_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, DEBUGFS_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, DEVPTS_SUPER_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, EFIVARFS_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, HUGETLBFS_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, MQUEUE_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, PROC_SUPER_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, PSTOREFS_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, SELINUX_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, SMACK_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, SECURITYFS_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, BPF_FS_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, TRACEFS_MAGIC) ||
+ F_TYPE_EQUAL(sfs->f_type, SYSFS_MAGIC);
+}
+
+static int recurse_fd(int fd, bool donate_fd, const struct stat *st, uid_t shift, bool is_toplevel) {
+ _cleanup_closedir_ DIR *d = NULL;
+ bool changed = false;
+ struct statfs sfs;
+ int r;
+
+ assert(fd >= 0);
+
+ if (fstatfs(fd, &sfs) < 0)
+ return -errno;
+
+ /* We generally want to permit crossing of mount boundaries when patching the UIDs/GIDs. However, we probably
+ * shouldn't do this for /proc and /sys if that is already mounted into place. Hence, let's stop the recursion
+ * when we hit procfs, sysfs or some other special file systems. */
+
+ r = is_fs_fully_userns_compatible(&sfs);
+ if (r < 0)
+ goto finish;
+ if (r > 0) {
+ r = 0; /* don't recurse */
+ goto finish;
+ }
+
+ /* Also, if we hit a read-only file system, then don't bother, skip the whole subtree */
+ if ((sfs.f_flags & ST_RDONLY) ||
+ access_fd(fd, W_OK) == -EROFS)
+ goto read_only;
+
+ if (S_ISDIR(st->st_mode)) {
+ if (!donate_fd) {
+ int copy;
+
+ copy = fcntl(fd, F_DUPFD_CLOEXEC, 3);
+ if (copy < 0) {
+ r = -errno;
+ goto finish;
+ }
+
+ fd = copy;
+ donate_fd = true;
+ }
+
+ d = take_fdopendir(&fd);
+ if (!d) {
+ r = -errno;
+ goto finish;
+ }
+
+ FOREACH_DIRENT_ALL(de, d, r = -errno; goto finish) {
+ struct stat fst;
+
+ if (dot_or_dot_dot(de->d_name))
+ continue;
+
+ if (fstatat(dirfd(d), de->d_name, &fst, AT_SYMLINK_NOFOLLOW) < 0) {
+ r = -errno;
+ goto finish;
+ }
+
+ if (S_ISDIR(fst.st_mode)) {
+ int subdir_fd;
+
+ subdir_fd = openat(dirfd(d), de->d_name, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME);
+ if (subdir_fd < 0) {
+ r = -errno;
+ goto finish;
+
+ }
+
+ r = recurse_fd(subdir_fd, true, &fst, shift, false);
+ if (r < 0)
+ goto finish;
+ if (r > 0)
+ changed = true;
+
+ } else {
+ r = patch_fd(dirfd(d), de->d_name, &fst, shift);
+ if (r < 0)
+ goto finish;
+ if (r > 0)
+ changed = true;
+ }
+ }
+ }
+
+ /* After we descended, also patch the directory itself. It's key to do this in this order so that the top-level
+ * directory is patched as very last object in the tree, so that we can use it as quick indicator whether the
+ * tree is properly chown()ed already. */
+ r = patch_fd(d ? dirfd(d) : fd, NULL, st, shift);
+ if (r == -EROFS)
+ goto read_only;
+ if (r > 0)
+ changed = true;
+
+ r = changed;
+ goto finish;
+
+read_only:
+ if (!is_toplevel) {
+ _cleanup_free_ char *name = NULL;
+
+ /* When we hit a ready-only subtree we simply skip it, but log about it. */
+ (void) fd_get_path(fd, &name);
+ log_debug("Skipping read-only file or directory %s.", strna(name));
+ r = changed;
+ }
+
+finish:
+ if (donate_fd)
+ safe_close(fd);
+
+ return r;
+}
+
+static int fd_patch_uid_internal(int fd, bool donate_fd, uid_t shift, uid_t range) {
+ struct stat st;
+ int r;
+
+ assert(fd >= 0);
+
+ /* Recursively adjusts the UID/GIDs of all files of a directory tree. This is used to automatically fix up an
+ * OS tree to the used user namespace UID range. Note that this automatic adjustment only works for UID ranges
+ * following the concept that the upper 16-bit of a UID identify the container, and the lower 16-bit are the actual
+ * UID within the container. */
+
+ if ((shift & 0xFFFF) != 0) {
+ /* We only support containers where the shift starts at a 2^16 boundary */
+ r = -EOPNOTSUPP;
+ goto finish;
+ }
+
+ if (shift == UID_BUSY_BASE) {
+ r = -EINVAL;
+ goto finish;
+ }
+
+ if (range != 0x10000) {
+ /* We only support containers with 16-bit UID ranges for the patching logic */
+ r = -EOPNOTSUPP;
+ goto finish;
+ }
+
+ if (fstat(fd, &st) < 0) {
+ r = -errno;
+ goto finish;
+ }
+
+ if ((uint32_t) st.st_uid >> 16 != (uint32_t) st.st_gid >> 16) {
+ /* We only support containers where the uid/gid container ID match */
+ r = -EBADE;
+ goto finish;
+ }
+
+ /* Try to detect if the range is already right. Of course, this a pretty drastic optimization, as we assume
+ * that if the top-level dir has the right upper 16-bit assigned, then everything below will have too... */
+ if (((uint32_t) (st.st_uid ^ shift) >> 16) == 0)
+ return 0;
+
+ /* Before we start recursively chowning, mark the top-level dir as "busy" by chowning it to the "busy"
+ * range. Should we be interrupted in the middle of our work, we'll see it owned by this user and will start
+ * chown()ing it again, unconditionally, as the busy UID is not a valid UID we'd everpick for ourselves. */
+
+ if ((st.st_uid & UID_BUSY_MASK) != UID_BUSY_BASE) {
+ if (fchown(fd,
+ UID_BUSY_BASE | (st.st_uid & ~UID_BUSY_MASK),
+ (gid_t) UID_BUSY_BASE | (st.st_gid & ~(gid_t) UID_BUSY_MASK)) < 0) {
+ r = -errno;
+ goto finish;
+ }
+ }
+
+ return recurse_fd(fd, donate_fd, &st, shift, true);
+
+finish:
+ if (donate_fd)
+ safe_close(fd);
+
+ return r;
+}
+
+int path_patch_uid(const char *path, uid_t shift, uid_t range) {
+ int fd;
+
+ fd = open(path, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME);
+ if (fd < 0)
+ return -errno;
+
+ return fd_patch_uid_internal(fd, true, shift, range);
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-21 13:58:10 +0000