From: Al Viro <viro@zeniv.linux.org.uk>
Date: Sun, 28 Feb 2016 00:31:01 +0000 (-0500)
Subject: should_follow_link(): validate ->d_seq after having decided to follow
X-Git-Tag: firefly_0821_release~176^2~475^2~101
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=6f4b352f004c696439c5b5d75a4edc3d0823e770;p=firefly-linux-kernel-4.4.55.git

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 f26cecbd6e73..930b51d6308b 100644
--- 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);
 }