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-Url: https://git.stricted.de/?a=commitdiff_plain;h=a7f775428b8f5808815c0e3004020cedb94cbe3b;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

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 e0881c0bd228..65a0e9d1ea48 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1712,6 +1712,11 @@ 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);
 }