#include "fd-util.h"
#include "fileio.h"
#include "fs-util.h"
-#include "glyph-util.h"
#include "log.h"
#include "macro.h"
#include "missing_fcntl.h"
return 0;
}
-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, unsigned 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), strna(n2), strna(user_b), path);
-}
-
-static int log_autofs_mount_point(int fd, const char *path, unsigned 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);
-}
-
-int chase_symlinks(const char *path, const char *original_root, unsigned flags, char **ret_path, int *ret_fd) {
- _cleanup_free_ char *buffer = NULL, *done = NULL, *root = NULL;
- _cleanup_close_ int fd = -1;
- unsigned max_follow = CHASE_SYMLINKS_MAX; /* how many symlinks to follow before giving up and returning ELOOP */
- bool exists = true, append_trail_slash = false;
- struct stat previous_stat;
- const char *todo;
- int r;
-
- assert(path);
-
- /* Either the file may be missing, or we return an fd to the final object, but both make no sense */
- if ((flags & CHASE_NONEXISTENT) && ret_fd)
- return -EINVAL;
-
- if ((flags & CHASE_STEP) && ret_fd)
- return -EINVAL;
-
- if (isempty(path))
- return -EINVAL;
-
- /* This is a lot like canonicalize_file_name(), but takes an additional "root" parameter, that allows following
- * symlinks relative to a root directory, instead of the root of the host.
- *
- * Note that "root" primarily matters if we encounter an absolute symlink. It is also used when following
- * relative symlinks to ensure they cannot be used to "escape" the root directory. The path parameter passed is
- * assumed to be already prefixed by it, except if the CHASE_PREFIX_ROOT flag is set, in which case it is first
- * prefixed accordingly.
- *
- * 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 it's special meaning
- * each time. The "todo" path always starts with at least one slash, the "done" path always ends in no
- * slash. 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 root parameter to tell this
- * function what to do when encountering a symlink with an absolute path as directory: prefix it by the
- * specified path.
- *
- * 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.
- *
- * 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.
- */
-
- /* A root directory of "/" or "" is identical to none */
- if (empty_or_root(original_root))
- original_root = NULL;
-
- if (!original_root && !ret_path && !(flags & (CHASE_NONEXISTENT|CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_STEP)) && 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 = open(path, O_PATH|O_CLOEXEC|((flags & CHASE_NOFOLLOW) ? O_NOFOLLOW : 0));
- if (r < 0)
- return -errno;
-
- *ret_fd = r;
- return 0;
- }
-
- if (original_root) {
- r = path_make_absolute_cwd(original_root, &root);
- 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. Note that dropping the
- * trailing slash should not change behaviour, since when opening it we specify O_DIRECTORY
- * anyway. Moreover at the end of this function after processing everything we'll always turn
- * the empty string back to "/". */
- delete_trailing_chars(root, "/");
- path_simplify(root);
-
- if (flags & CHASE_PREFIX_ROOT) {
- /* We don't support relative paths in combination with a root directory */
- if (!path_is_absolute(path))
- return -EINVAL;
-
- path = prefix_roota(root, path);
- }
- }
-
- r = path_make_absolute_cwd(path, &buffer);
- if (r < 0)
- return r;
-
- fd = open(root ?: "/", O_CLOEXEC|O_DIRECTORY|O_PATH);
- if (fd < 0)
- return -errno;
-
- if (flags & CHASE_SAFE)
- if (fstat(fd, &previous_stat) < 0)
- return -errno;
-
- if (flags & CHASE_TRAIL_SLASH)
- append_trail_slash = endswith(buffer, "/") || endswith(buffer, "/.");
-
- if (root) {
- /* If we are operating on a root directory, let's take the root directory as it is. */
-
- todo = path_startswith(buffer, root);
- if (!todo)
- return log_full_errno(flags & CHASE_WARN ? LOG_WARNING : LOG_DEBUG,
- SYNTHETIC_ERRNO(ECHRNG),
- "Specified path '%s' is outside of specified root directory '%s', refusing to resolve.",
- path, root);
-
- done = strdup(root);
- } else {
- todo = buffer;
- done = strdup("/");
- }
-
- for (;;) {
- _cleanup_free_ char *first = NULL;
- _cleanup_close_ int child = -1;
- struct stat st;
- const char *e;
-
- r = path_find_first_component(&todo, 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 = -1;
-
- /* 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))
- continue;
-
- parent = dirname_malloc(done);
- if (!parent)
- return -ENOMEM;
-
- /* Don't allow this to leave the root dir. */
- if (root &&
- path_startswith(done, root) &&
- !path_startswith(parent, root))
- continue;
-
- free_and_replace(done, parent);
-
- if (flags & CHASE_STEP)
- goto chased_one;
-
- fd_parent = openat(fd, "..", O_CLOEXEC|O_NOFOLLOW|O_PATH);
- if (fd_parent < 0)
- return -errno;
-
- if (flags & CHASE_SAFE) {
- if (fstat(fd_parent, &st) < 0)
- return -errno;
-
- if (unsafe_transition(&previous_stat, &st))
- return log_unsafe_transition(fd, fd_parent, path, flags);
-
- previous_stat = st;
- }
-
- safe_close(fd);
- fd = TAKE_FD(fd_parent);
-
- continue;
- }
-
- /* Otherwise let's see what this is. */
- child = openat(fd, first, O_CLOEXEC|O_NOFOLLOW|O_PATH);
- if (child < 0) {
- if (errno == ENOENT &&
- (flags & CHASE_NONEXISTENT) &&
- (isempty(todo) || path_is_safe(todo))) {
- /* If CHASE_NONEXISTENT is set, and the path does not exist, then
- * that's OK, return what we got so far. But don't allow this if the
- * remaining path contains "../" or something else weird. */
-
- if (!path_extend(&done, first, todo))
- return -ENOMEM;
-
- exists = false;
- break;
- }
-
- return -errno;
- }
-
- if (fstat(child, &st) < 0)
- return -errno;
- if ((flags & CHASE_SAFE) &&
- unsafe_transition(&previous_stat, &st))
- return log_unsafe_transition(fd, child, path, flags);
-
- previous_stat = st;
-
- if ((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.st_mode) && !((flags & CHASE_NOFOLLOW) && isempty(todo))) {
- _cleanup_free_ char *destination = NULL;
-
- /* 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
- * directory as base. */
-
- safe_close(fd);
- fd = open(root ?: "/", O_CLOEXEC|O_DIRECTORY|O_PATH);
- if (fd < 0)
- return -errno;
-
- if (flags & CHASE_SAFE) {
- if (fstat(fd, &st) < 0)
- return -errno;
-
- if (unsafe_transition(&previous_stat, &st))
- return log_unsafe_transition(child, fd, path, flags);
-
- previous_stat = st;
- }
-
- /* Note that we do not revalidate the root, we take it as is. */
- r = free_and_strdup(&done, empty_to_root(root));
- 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 & 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;
-
- /* And iterate again, but go one directory further down. */
- safe_close(fd);
- fd = TAKE_FD(child);
- }
-
- if (ret_path)
- *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 & CHASE_STEP)
- return 1;
-
- return exists;
-
-chased_one:
- if (ret_path) {
- const char *e;
-
- /* todo may contain slashes at the beginning. */
- r = path_find_first_component(&todo, 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;
-}
-
-int chase_symlinks_and_open(
- const char *path,
- const char *root,
- unsigned chase_flags,
- int open_flags,
- char **ret_path) {
-
- _cleanup_close_ int path_fd = -1;
- _cleanup_free_ char *p = NULL;
- int r;
-
- if (chase_flags & CHASE_NONEXISTENT)
- return -EINVAL;
-
- if (empty_or_root(root) && !ret_path && (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE)) == 0) {
- /* Shortcut this call if none of the special features of this call are requested */
- r = open(path, open_flags);
- if (r < 0)
- return -errno;
-
- return r;
- }
-
- r = chase_symlinks(path, root, chase_flags, ret_path ? &p : NULL, &path_fd);
- if (r < 0)
- return r;
- assert(path_fd >= 0);
-
- r = fd_reopen(path_fd, open_flags);
- if (r < 0)
- return r;
-
- if (ret_path)
- *ret_path = TAKE_PTR(p);
-
- return r;
-}
-
-int chase_symlinks_and_opendir(
- const char *path,
- const char *root,
- unsigned chase_flags,
- char **ret_path,
- DIR **ret_dir) {
-
- _cleanup_close_ int path_fd = -1;
- _cleanup_free_ char *p = NULL;
- DIR *d;
- int r;
-
- if (!ret_dir)
- return -EINVAL;
- if (chase_flags & CHASE_NONEXISTENT)
- return -EINVAL;
-
- if (empty_or_root(root) && !ret_path && (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE)) == 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_symlinks(path, root, chase_flags, ret_path ? &p : NULL, &path_fd);
- if (r < 0)
- return r;
- assert(path_fd >= 0);
-
- d = opendir(FORMAT_PROC_FD_PATH(path_fd));
- if (!d)
- return -errno;
-
- if (ret_path)
- *ret_path = TAKE_PTR(p);
-
- *ret_dir = d;
- return 0;
-}
-
-int chase_symlinks_and_stat(
- const char *path,
- const char *root,
- unsigned chase_flags,
- char **ret_path,
- struct stat *ret_stat,
- int *ret_fd) {
-
- _cleanup_close_ int path_fd = -1;
- _cleanup_free_ char *p = NULL;
- int r;
-
- assert(path);
- assert(ret_stat);
-
- if (chase_flags & CHASE_NONEXISTENT)
- return -EINVAL;
-
- if (empty_or_root(root) && !ret_path && (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE)) == 0) {
- /* Shortcut this call if none of the special features of this call are requested */
- if (stat(path, ret_stat) < 0)
- return -errno;
-
- return 1;
- }
-
- r = chase_symlinks(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);
- if (ret_fd)
- *ret_fd = TAKE_FD(path_fd);
-
- return 1;
-}
-
int access_fd(int fd, int mode) {
/* Like access() but operates on an already open fd */
projects / thirdparty / systemd.git / blobdiff