should_follow_link(): validate ->d_seq after having decided to follow
... otherwise d_is_symlink() above might have nothing to do with
the inode value we've got.
Cc: stable@vger.kernel.org # v4.2+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namei.c b/fs/namei.c
index e0881c0b..65a0e9d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1712,6 +1712,11 @@
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);
}