tree afb1bebd5515d5a1642bb9afb6adcd23d0fd6e6d
parent fd3fc0b4d7305fa7246622dcc0dec69c42443f45
author Al Viro <viro@ZenIV.linux.org.uk> 1487488527 +0000
committer Linus Torvalds <torvalds@linux-foundation.org> 1487526871 -0800

Fix missing sanity check in /dev/sg

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>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>