SymbX/systemd
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

chase-symlinks: chase_symlinks_at() AT_FDCWD fixes

Browse Source 
- Whether we should return an absolute path or not is irrelevant
to whether CHASE_AT_RESOLVE_IN_ROOT is set. We should only return
an absolute path if we are provided one and the directory file
descriptor is AT_FDCWD
- When the directory file descriptor is AT_FDCWD, we should always
resolve symlinks against "/". Currently, if the directory file
descriptor is AT_FDCWD and CHASE_AT_RESOLVE_IN_ROOT is set, we
resolve symlinks against the current working directory which is
almost always not going to be what the caller wants.
- Currently, if we provide an absolute path with a positive directory
file descriptor without CHASE_AT_RESOLVE_IN_ROOT SET, we interpret
the path relative to "/" instead of the given directory file descriptor.
Let's make sure that when we're given a positive directory file
descriptor, we always resolve the given path relative to it.
This commit is contained in:
Daan De Meyer
2023-02-07 16:36:54 +01:00
parent 8586e8ab84
commit c677e13c35
2 changed files with 59 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/basic/chase-symlinks.c
+23 -12
View File
@@ -102,20 +102,22 @@ int chase_symlinks_at(
path = ".";
/* This function resolves symlinks of the path relative to the given directory file descriptor. If
* CHASE_SYMLINKS_RESOLVE_IN_ROOT is specified, symlinks are resolved relative to the given directory
* file descriptor. Otherwise, they are resolved relative to the root directory of the host.
* CHASE_SYMLINKS_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 CHASE_SYMLINKS_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 ensure they cannot be used to "escape" the given
* directory file descriptor. The "path" parameter is always interpreted relative to the given
* directory file descriptor. If the given directory file descriptor is AT_FDCWD and "path" is
* absolute, it is interpreted 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.
*
* If "dir_fd" is a valid directory fd, "path" is an absolute path and "ret_path" is not NULL, this
* functions returns a relative path in "ret_path" because openat() like functions generally ignore
* the directory fd if they are provided with an absolute path. On the other hand, if "dir_fd" is
* AT_FDCWD and "path" is an absolute path, we need to return an absolute path in "ret_path" because
* 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 "/".
*
@@ -177,21 +179,30 @@ int chase_symlinks_at(
if (!buffer)
return -ENOMEM;
bool need_absolute = !FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT) && path_is_absolute(path);
/* 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. */
bool need_absolute = dir_fd == AT_FDCWD && path_is_absolute(path);
if (need_absolute) {
done = strdup("/");
if (!done)
return -ENOMEM;
}
if (FLAGS_SET(flags, CHASE_AT_RESOLVE_IN_ROOT))
/* If we get AT_FDCWD, we always resolve symlinks relative to the host's root. Only if a positive
* directory file descriptor is provided will we 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_AT_RESOLVE_IN_ROOT) || !path_is_absolute(path))
/* 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. */
if (dir_fd >= 0 || !path_is_absolute(path))
fd = openat(dir_fd, ".", O_CLOEXEC|O_DIRECTORY|O_PATH);
else
fd = open("/", O_CLOEXEC|O_DIRECTORY|O_PATH);
src/test/test-fs-util.c
+36
View File
@@ -430,6 +430,42 @@ TEST(chase_symlinks) {
assert_se(rm_rf(temp, REMOVE_ROOT|REMOVE_PHYSICAL) >= 0);
}
TEST(chase_symlinks_at) {
_cleanup_(rm_rf_physical_and_freep) char *t = NULL;
_cleanup_close_ int tfd = -EBADF, fd = -EBADF;
_cleanup_free_ char *result = NULL;
const char *p;
assert_se((tfd = mkdtemp_open(NULL, 0, &t)) >= 0);
/* Test that AT_FDCWD with CHASE_AT_RESOLVE_IN_ROOT resolves against / and not the current working
* directory. */
assert_se(symlinkat("/usr", tfd, "abc") >= 0);
p = strjoina(t, "/abc");
assert_se(chase_symlinks_at(AT_FDCWD, p, CHASE_AT_RESOLVE_IN_ROOT, &result, NULL) >= 0);
assert_se(streq(result, "/usr"));
result = mfree(result);
/* Test that absolute path or not are the same when resolving relative to a directory file
* descriptor and that we always get a relative path back. */
assert_se(fd = openat(tfd, "def", O_CREAT|O_CLOEXEC, 0700) >= 0);
fd = safe_close(fd);
assert_se(symlinkat("/def", tfd, "qed") >= 0);
assert_se(chase_symlinks_at(tfd, "qed", CHASE_AT_RESOLVE_IN_ROOT, &result, NULL) >= 0);
assert_se(streq(result, "def"));
result = mfree(result);
assert_se(chase_symlinks_at(tfd, "/qed", CHASE_AT_RESOLVE_IN_ROOT, &result, NULL) >= 0);
assert_se(streq(result, "def"));
result = mfree(result);
/* Valid directory file descriptor without CHASE_AT_RESOLVE_IN_ROOT should resolve symlinks against
* host's root. */
assert_se(chase_symlinks_at(tfd, "/qed", 0, &result, NULL) == -ENOENT);
}
TEST(unlink_noerrno) {
char *name;
int fd;