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authorLinus Torvalds <torvalds@linux-foundation.org>2017-04-02 17:10:08 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-04-15 09:34:52 -0700
commitc0eb027e5aef70b71e5a38ee3e264dc0b497f343 (patch)
parent1bf4b1268e66d9364fc6fd41f906bc01458530ac (diff)
vfs: don't do RCU lookup of empty pathnames
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 <dvyukov@google.com> Reported-by: Vegard Nossum <vegard.nossum@gmail.com> Acked-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 3 insertions, 0 deletions
diff --git a/fs/namei.c b/fs/namei.c
index d41fab78798b..19dcf62133cc 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;