linux-kernel - [PATCH 3.16.y-ckt 048/142] do_last(): don't let a bogus return value from ->open() et.al. to confuse us

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Message-Id: <1458643271-4227-49-git-send-email-luis.henriques@canonical.com>
Date:	Tue, 22 Mar 2016 10:39:37 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 048/142] do_last(): don't let a bogus return value from ->open() et.al. to confuse us

3.16.7-ckt26 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Al Viro <viro@...iv.linux.org.uk>

commit c80567c82ae4814a41287618e315a60ecf513be6 upstream.

... into returning a positive to path_openat(), which would interpret that
as "symlink had been encountered" and proceed to corrupt memory, etc.
It can only happen due to a bug in some ->open() instance or in some LSM
hook, etc., so we report any such event *and* make sure it doesn't trick
us into further unpleasantness.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 fs/namei.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index 8a0c3d9d8298..34f8224be4ed 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3108,6 +3108,10 @@ opened:
 			goto exit_fput;
 	}
 out:
+	if (unlikely(error > 0)) {
+		WARN_ON(1);
+		error = -EINVAL;
+	}
 	if (got_write)
 		mnt_drop_write(nd->path.mnt);
 	path_put(&save_parent);