From: Al Viro <viro@ZenIV.linux.org.uk>
Date: Sun, 19 Feb 2017 07:15:27 +0000 (+0000)
Subject: Fix missing sanity check in /dev/sg
X-Git-Tag: v3.2.87~49
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=fd3a84ea1b8650f6929462996f8d96d271f9d0d0;p=pandora-kernel.git

Fix missing sanity check in /dev/sg

commit 137d01df511b3afe1f05499aea05f3bafc0fb221 upstream.

What happens is that a write to /dev/sg is given a request with non-zero
->iovec_count combined with zero ->dxfer_len.  Or with ->dxferp pointing
to an array full of empty iovecs.

Having write permission to /dev/sg shouldn't be equivalent to the
ability to trigger BUG_ON() while holding spinlocks...

Found by Dmitry Vyukov and syzkaller.

[ The BUG_ON() got changed to a WARN_ON_ONCE(), but this fixes the
  underlying issue.  - Linus ]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: we're not using iov_iter, but can check the
 byte length after truncation]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

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