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Backport of the following upstream commit:
From bef8e8e577368697b2e6f85183b1dbc99e0e520f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Tue, 30 Nov 2021 22:29:05 +0100
Subject: [PATCH 3/3] shared/rm-rf: loop over nested directories instead of
instead of recursing
To remove directory structures, we need to remove the innermost items first,
and then recursively remove higher-level directories. We would recursively
descend into directories and invoke rm_rf_children and rm_rm_children_inner.
This is problematic when too many directories are nested.
Instead, let's create a "TODO" queue. In the the queue, for each level we
hold the DIR* object we were working on, and the name of the directory. This
allows us to leave a partially-processed directory, and restart the removal
loop one level down. When done with the inner directory, we use the name to
unlinkat() it from the parent, and proceed with the removal of other items.
Because the nesting is increased by one level, it is best to view this patch
with -b/--ignore-space-change.
This fixes CVE-2021-3997, https://bugzilla.redhat.com/show_bug.cgi?id=2024639.
The issue was reported and patches reviewed by Qualys Team.
Mauro Matteo Cascella and Riccardo Schirone from Red Hat handled the disclosure.
CVE: CVE-2021-3997
Upstream-Status: Backport [http://archive.ubuntu.com/ubuntu/pool/main/s/systemd/systemd_245.4-4ubuntu3.15.debian.tar.xz]
Signed-off-by: Purushottam Choudhary <Purushottam.Choudhary@kpit.com>
---
src/basic/rm-rf.c | 161 +++++++++++++++++++++++++++++++--------------
1 file changed, 113 insertions(+), 48 deletions(-)
--- a/src/basic/rm-rf.c
+++ b/src/basic/rm-rf.c
@@ -26,12 +26,13 @@
return !is_temporary_fs(sfs) && !is_cgroup_fs(sfs);
}
-static int rm_rf_children_inner(
+static int rm_rf_inner_child(
int fd,
const char *fname,
int is_dir,
RemoveFlags flags,
- const struct stat *root_dev) {
+ const struct stat *root_dev,
+ bool allow_recursion) {
struct stat st;
int r, q = 0;
@@ -49,9 +50,7 @@
}
if (is_dir) {
- _cleanup_close_ int subdir_fd = -1;
-
- /* if root_dev is set, remove subdirectories only if device is same */
+ /* If root_dev is set, remove subdirectories only if device is same */
if (root_dev && st.st_dev != root_dev->st_dev)
return 0;
@@ -63,7 +62,6 @@
return 0;
if ((flags & REMOVE_SUBVOLUME) && st.st_ino == 256) {
-
/* This could be a subvolume, try to remove it */
r = btrfs_subvol_remove_fd(fd, fname, BTRFS_REMOVE_RECURSIVE|BTRFS_REMOVE_QUOTA);
@@ -77,13 +75,16 @@
return 1;
}
- subdir_fd = openat(fd, fname, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME);
+ if (!allow_recursion)
+ return -EISDIR;
+
+ int subdir_fd = openat(fd, fname, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME);
if (subdir_fd < 0)
return -errno;
/* We pass REMOVE_PHYSICAL here, to avoid doing the fstatfs() to check the file system type
* again for each directory */
- q = rm_rf_children(TAKE_FD(subdir_fd), flags | REMOVE_PHYSICAL, root_dev);
+ q = rm_rf_children(subdir_fd, flags | REMOVE_PHYSICAL, root_dev);
} else if (flags & REMOVE_ONLY_DIRECTORIES)
return 0;
@@ -96,64 +97,128 @@
return 1;
}
+typedef struct TodoEntry {
+ DIR *dir; /* A directory that we were operating on. */
+ char *dirname; /* The filename of that directory itself. */
+} TodoEntry;
+
+static void free_todo_entries(TodoEntry **todos) {
+ for (TodoEntry *x = *todos; x && x->dir; x++) {
+ closedir(x->dir);
+ free(x->dirname);
+ }
+
+ freep(todos);
+}
+
int rm_rf_children(
int fd,
RemoveFlags flags,
const struct stat *root_dev) {
- _cleanup_closedir_ DIR *d = NULL;
- struct dirent *de;
+ _cleanup_(free_todo_entries) TodoEntry *todos = NULL;
+ size_t n_todo = 0, allocated = 0;
+ _cleanup_free_ char *dirname = NULL; /* Set when we are recursing and want to delete ourselves */
int ret = 0, r;
- assert(fd >= 0);
+ /* Return the first error we run into, but nevertheless try to go on.
+ * The passed fd is closed in all cases, including on failure. */
- /* This returns the first error we run into, but nevertheless tries to go on. This closes the passed
- * fd, in all cases, including on failure. */
+ for (;;) { /* This loop corresponds to the directory nesting level. */
+ _cleanup_closedir_ DIR *d = NULL;
+ struct dirent *de;
+
+ if (n_todo > 0) {
+ /* We know that we are in recursion here, because n_todo is set.
+ * We need to remove the inner directory we were operating on. */
+ assert(dirname);
+ r = unlinkat(dirfd(todos[n_todo-1].dir), dirname, AT_REMOVEDIR);
+ if (r < 0 && r != -ENOENT && ret == 0)
+ ret = r;
+ dirname = mfree(dirname);
+
+ /* And now let's back out one level up */
+ n_todo --;
+ d = TAKE_PTR(todos[n_todo].dir);
+ dirname = TAKE_PTR(todos[n_todo].dirname);
+
+ assert(d);
+ fd = dirfd(d); /* Retrieve the file descriptor from the DIR object */
+ assert(fd >= 0);
+ } else {
+ next_fd:
+ assert(fd >= 0);
+ d = fdopendir(fd);
+ if (!d) {
+ safe_close(fd);
+ return -errno;
+ }
+ fd = dirfd(d); /* We donated the fd to fdopendir(). Let's make sure we sure we have
+ * the right descriptor even if it were to internally invalidate the
+ * one we passed. */
+
+ if (!(flags & REMOVE_PHYSICAL)) {
+ struct statfs sfs;
+
+ if (fstatfs(fd, &sfs) < 0)
+ return -errno;
+
+ if (is_physical_fs(&sfs)) {
+ /* We refuse to clean physical file systems with this call, unless
+ * explicitly requested. This is extra paranoia just to be sure we
+ * never ever remove non-state data. */
+
+ _cleanup_free_ char *path = NULL;
+
+ (void) fd_get_path(fd, &path);
+ return log_error_errno(SYNTHETIC_ERRNO(EPERM),
+ "Attempted to remove disk file system under \"%s\", and we can't allow that.",
+ strna(path));
+ }
+ }
+ }
- d = fdopendir(fd);
- if (!d) {
- safe_close(fd);
- return -errno;
- }
+ FOREACH_DIRENT_ALL(de, d, return -errno) {
+ int is_dir;
- if (!(flags & REMOVE_PHYSICAL)) {
- struct statfs sfs;
+ if (dot_or_dot_dot(de->d_name))
+ continue;
- if (fstatfs(dirfd(d), &sfs) < 0)
- return -errno;
- }
+ is_dir = de->d_type == DT_UNKNOWN ? -1 : de->d_type == DT_DIR;
- if (is_physical_fs(&sfs)) {
- /* We refuse to clean physical file systems with this call, unless explicitly
- * requested. This is extra paranoia just to be sure we never ever remove non-state
- * data. */
-
- _cleanup_free_ char *path = NULL;
-
- (void) fd_get_path(fd, &path);
- return log_error_errno(SYNTHETIC_ERRNO(EPERM),
- "Attempted to remove disk file system under \"%s\", and we can't allow that.",
- strna(path));
- }
- }
+ r = rm_rf_inner_child(fd, de->d_name, is_dir, flags, root_dev, false);
+ if (r == -EISDIR) {
+ /* Push the current working state onto the todo list */
- FOREACH_DIRENT_ALL(de, d, return -errno) {
- int is_dir;
+ if (!GREEDY_REALLOC0(todos, allocated, n_todo + 2))
+ return log_oom();
- if (dot_or_dot_dot(de->d_name))
- continue;
+ _cleanup_free_ char *newdirname = strdup(de->d_name);
+ if (!newdirname)
+ return log_oom();
- is_dir =
- de->d_type == DT_UNKNOWN ? -1 :
- de->d_type == DT_DIR;
-
- r = rm_rf_children_inner(dirfd(d), de->d_name, is_dir, flags, root_dev);
- if (r < 0 && r != -ENOENT && ret == 0)
- ret = r;
- }
+ int newfd = openat(fd, de->d_name,
+ O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME);
+ if (newfd >= 0) {
+ todos[n_todo++] = (TodoEntry) { TAKE_PTR(d), TAKE_PTR(dirname) };
+ fd = newfd;
+ dirname = TAKE_PTR(newdirname);
+
+ goto next_fd;
- if (FLAGS_SET(flags, REMOVE_SYNCFS) && syncfs(dirfd(d)) < 0 && ret >= 0)
- ret = -errno;
+ } else if (errno != -ENOENT && ret == 0)
+ ret = -errno;
+
+ } else if (r < 0 && r != -ENOENT && ret == 0)
+ ret = r;
+ }
+
+ if (FLAGS_SET(flags, REMOVE_SYNCFS) && syncfs(fd) < 0 && ret >= 0)
+ ret = -errno;
+
+ if (n_todo == 0)
+ break;
+ }
return ret;
}
@@ -250,5 +315,5 @@
if (FLAGS_SET(flags, REMOVE_ONLY_DIRECTORIES|REMOVE_SUBVOLUME))
return -EINVAL;
- return rm_rf_children_inner(fd, name, -1, flags, NULL);
+ return rm_rf_inner_child(fd, name, -1, flags, NULL, true);
}
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