vfs: don't do RCU lookup of empty pathnames
c0eb027e · Linus Torvalds <[email protected]> · 2017-04-02 17:10:08 -07:00
Normal pathname lookup doesn't allow empty pathnames, but using
AT_EMPTY_PATH (with name_to_handle_at() or fstatat(), for example) you
can trigger an empty pathname lookup.
And not only is the RCU lookup in that case entirely unnecessary
(because we'll obviously immediately finalize the end result), it is
actively wrong.
Why? An empth path is a special case that will return the original
'dirfd' dentry - and that dentry may not actually be RCU-free'd,
resulting in a potential use-after-free if we were to initialize the
path lazily under the RCU read lock and depend on complete_walk()
finalizing the dentry.
Found by syzkaller and KASAN.
Reported-by: Dmitry Vyukov <[email protected]>
Reported-by: Vegard Nossum <[email protected]>
Acked-by: Al Viro <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
- Commit
- c0eb027e5aef70b71e5a38ee3e264dc0b497f343
- Parents
- 1bf4b126
Changes
1 files changed · +3 −0
diff --git a/fs/namei.c b/fs/namei.c
index d41fab7..19dcf62 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2145,6 +2145,9 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
int retval = 0;
const char *s = nd->name->name;
+ if (!*s)
+ flags &= ~LOOKUP_RCU;
+
nd->last_type = LAST_ROOT; /* if there are only slashes... */
nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT;
nd->depth = 0;