should_follow_link(): validate ->d_seq after having decided to follow

commit a7f775428b8f5808815c0e3004020cedb94cbe3b upstream.

... otherwise d_is_symlink() above might have nothing to do with
the inode value we've got.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/namei.c b/fs/namei.c
index f26cecbd6e73450d0efc068f066d245b4da7406b..930b51d6308b6ff98ac3f297fc6ba4768881c2ef 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1711,6 +1711,11 @@ static inline int should_follow_link(struct nameidata *nd, struct path *link,
                return 0;
        if (!follow)
                return 0;
+       /* make sure that d_is_symlink above matches inode */
+       if (nd->flags & LOOKUP_RCU) {
+               if (read_seqcount_retry(&link->dentry->d_seq, seq))
+                       return -ECHILD;
+       }
        return pick_link(nd, link, inode, seq);
 }