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fs-util: add new CHASE_NON_EXISTING flag to chase_symlinks() 

This new flag controls whether to consider a problem if the referenced path
doesn't actually exist. If specified it's OK if the final file doesn't exist.

Note that this permits one or more final components of the path not to exist,
but these must not contain "../" for safety reasons (or, to be extra safe,
neither "./" and a couple of others, i.e. what path_is_safe() permits).

This new flag is useful when resolving paths before issuing an mkdir() or
open(O_CREAT) on a path, as it permits that the file or directory is created
later.

The return code of chase_symlinks() is changed to return 1 if the file exists,
and 0 if it doesn't. The latter is only returned in case CHASE_NON_EXISTING is
set.
This commit is contained in:
Lennart Poettering 2016-11-29 18:02:45 +01:00
parent c4f4fce79e
commit a9fb08670f
3 changed files with 66 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
src/basic/fs-util.c
View File

@ -602,6 +602,7 @@ int chase_symlinks(const char *path, const char *original_root, unsigned flags,
_cleanup_free_ char *buffer = NULL, *done = NULL, *root = NULL;
_cleanup_close_ int fd = -1;
unsigned max_follow = 32; /* how many symlinks to follow before giving up and returning ELOOP */
bool exists = true;
char *todo;
int r;
@ -707,8 +708,25 @@ int chase_symlinks(const char *path, const char *original_root, unsigned flags,
/* Otherwise let's see what this is. */
child = openat(fd, first + n, O_CLOEXEC|O_NOFOLLOW|O_PATH);
if (child < 0)
if (child < 0) {
if (errno == ENOENT &&
(flags & CHASE_NON_EXISTING) &&
(isempty(todo) || path_is_safe(todo))) {
/* If CHASE_NON_EXISTING 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 "./"
* or something else weird. */
if (!strextend(&done, first, todo, NULL))
return -ENOMEM;
exists = false;
break;
}
return -errno;
}
if (fstat(child, &st) < 0)
return -errno;
@ -793,5 +811,5 @@ int chase_symlinks(const char *path, const char *original_root, unsigned flags,
*ret = done;
done = NULL;
return 0;
return exists;
}

1
src/basic/fs-util.h
View File

@ -80,6 +80,7 @@ int inotify_add_watch_fd(int fd, int what, uint32_t mask);
enum {
CHASE_PREFIX_ROOT = 1, /* If set, the specified path will be prefixed by the specified root before beginning the iteration */
CHASE_NON_EXISTING = 2, /* If set, it's OK if the path doesn't actually exist. */
};
int chase_symlinks(const char *path_with_prefix, const char *root, unsigned flags, char **ret);

56
src/test/test-fs-util.c
View File

@ -63,7 +63,7 @@ static void test_chase_symlinks(void) {
/* Paths that use symlinks underneath the "root" */
r = chase_symlinks(p, NULL, 0, &result);
assert_se(r >= 0);
assert_se(r > 0);
assert_se(path_equal(result, "/usr"));
result = mfree(result);
@ -71,10 +71,15 @@ static void test_chase_symlinks(void) {
assert_se(r == -ENOENT);
q = strjoina(temp, "/usr");
r = chase_symlinks(p, temp, CHASE_NON_EXISTING, &result);
assert_se(r == 0);
assert_se(path_equal(result, q));
assert_se(mkdir(q, 0700) >= 0);
r = chase_symlinks(p, temp, 0, &result);
assert_se(r >= 0);
assert_se(r > 0);
assert_se(path_equal(result, q));
p = strjoina(temp, "/slash");
@ -82,12 +87,12 @@ static void test_chase_symlinks(void) {
result = mfree(result);
r = chase_symlinks(p, NULL, 0, &result);
assert_se(r >= 0);
assert_se(r > 0);
assert_se(path_equal(result, "/"));
result = mfree(result);
r = chase_symlinks(p, temp, 0, &result);
assert_se(r >= 0);
assert_se(r > 0);
assert_se(path_equal(result, temp));
/* Paths that would "escape" outside of the "root" */
@ -97,21 +102,21 @@ static void test_chase_symlinks(void) {
result = mfree(result);
r = chase_symlinks(p, temp, 0, &result);
assert_se(r == 0 && path_equal(result, temp));
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, 0, &result);
assert_se(r == 0 && path_equal(result, q));
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, 0, &result);
assert_se(r == 0 && path_equal(result, q));
assert_se(r > 0 && path_equal(result, q));
/* Paths that contain repeated slashes */
@ -120,24 +125,24 @@ static void test_chase_symlinks(void) {
result = mfree(result);
r = chase_symlinks(p, NULL, 0, &result);
assert_se(r >= 0);
assert_se(r > 0);
assert_se(path_equal(result, "/usr"));
result = mfree(result);
r = chase_symlinks(p, temp, 0, &result);
assert_se(r >= 0);
assert_se(r > 0);
assert_se(path_equal(result, q));
/* Paths using . */
result = mfree(result);
r = chase_symlinks("/etc/./.././", NULL, 0, &result);
assert_se(r >= 0);
assert_se(r > 0);
assert_se(path_equal(result, "/"));
result = mfree(result);
r = chase_symlinks("/etc/./.././", "/etc", 0, &result);
assert_se(r == 0 && path_equal(result, "/etc"));
assert_se(r > 0 && path_equal(result, "/etc"));
result = mfree(result);
r = chase_symlinks("/etc/machine-id/foo", NULL, 0, &result);
@ -151,6 +156,35 @@ static void test_chase_symlinks(void) {
r = chase_symlinks(p, NULL, 0, &result);
assert_se(r == -ELOOP);
/* Path which doesn't exist */
p = strjoina(temp, "/idontexist");
r = chase_symlinks(p, NULL, 0, &result);
assert_se(r == -ENOENT);
r = chase_symlinks(p, NULL, CHASE_NON_EXISTING, &result);
assert_se(r == 0);
assert_se(path_equal(result, p));
result = mfree(result);
p = strjoina(temp, "/idontexist/meneither");
r = chase_symlinks(p, NULL, 0, &result);
assert_se(r == -ENOENT);
r = chase_symlinks(p, NULL, CHASE_NON_EXISTING, &result);
assert_se(r == 0);
assert_se(path_equal(result, p));
result = mfree(result);
/* Path which doesn't exist, but contains weird stuff */
p = strjoina(temp, "/idontexist/..");
r = chase_symlinks(p, NULL, 0, &result);
assert_se(r == -ENOENT);
r = chase_symlinks(p, NULL, CHASE_NON_EXISTING, &result);
assert_se(r == -ENOENT);
assert_se(rm_rf(temp, REMOVE_ROOT|REMOVE_PHYSICAL) >= 0);
}