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fs-util: change chase_symlinks() behaviour in regards to escaping the root dir 

Previously, we'd generate an EINVAL error if it is attempted to escape a root
directory with relative ".." symlinks. With this commit this is changed so that
".." from the root directory is a NOP, following the kernel's own behaviour
where /.. is equivalent to /.

As suggested by @keszybz.
This commit is contained in:
Lennart Poettering 2016-11-29 15:54:42 +01:00
parent df878e682d
commit a4eaf3cf82
2 changed files with 11 additions and 9 deletions
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12
src/basic/fs-util.c
View File

@ -611,8 +611,8 @@ int chase_symlinks(const char *path, const char *_root, char **ret) {
* 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. (For cases where this is
* attempted -EINVAL is returned.). The path parameter passed shall *not* be prefixed by it.
* relative symlinks to ensure they cannot be used to "escape" the root directory. The path parameter passed
* shall *not* be prefixed by it.
*
* 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
@ -674,18 +674,20 @@ int chase_symlinks(const char *path, const char *_root, char **ret) {
_cleanup_free_ char *parent = NULL;
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 (isempty(done) || path_equal(done, "/"))
return -EINVAL;
continue;
parent = dirname_malloc(done);
if (!parent)
return -ENOMEM;
/* Don't allow this to leave the root dir */
/* Don't allow this to leave the root dir. */
if (root &&
path_startswith(done, root) &&
!path_startswith(parent, root))
return -EINVAL;
continue;
free_and_replace(done, parent);

8
src/test/test-fs-util.c
View File

@ -97,21 +97,21 @@ static void test_chase_symlinks(void) {
result = mfree(result);
r = chase_symlinks(p, temp, &result);
assert_se(r == -EINVAL);
assert_se(r == 0 && path_equal(result, temp));
p = strjoina(temp, "/6dotsusr");
assert_se(symlink("../../../usr", p) >= 0);
result = mfree(result);
r = chase_symlinks(p, temp, &result);
assert_se(r == -EINVAL);
assert_se(r == 0 && path_equal(result, q));
p = strjoina(temp, "/top/8dotsusr");
assert_se(symlink("../../../../usr", p) >= 0);
result = mfree(result);
r = chase_symlinks(p, temp, &result);
assert_se(r == -EINVAL);
assert_se(r == 0 && path_equal(result, q));
/* Paths that contain repeated slashes */
@ -137,7 +137,7 @@ static void test_chase_symlinks(void) {
result = mfree(result);
r = chase_symlinks("/etc/./.././", "/etc", &result);
assert_se(r == -EINVAL);
assert_se(r == 0 && path_equal(result, "/etc"));
result = mfree(result);
r = chase_symlinks("/etc/machine-id/foo", NULL, &result);