From a975e8e81e5533786b2120d053203b47e07d6c1d Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sun, 19 Feb 2017 07:15:27 +0000 Subject: [PATCH] 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 Reported-by: Dmitry Vyukov Reviewed-by: Christoph Hellwig Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- drivers/scsi/sg.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c index dbe5b4b95df0..121de0aaa6ad 100644 --- a/drivers/scsi/sg.c +++ b/drivers/scsi/sg.c @@ -1753,6 +1753,10 @@ sg_start_req(Sg_request *srp, unsigned char *cmd) return res; iov_iter_truncate(&i, hp->dxfer_len); + if (!iov_iter_count(&i)) { + kfree(iov); + return -EINVAL; + } res = blk_rq_map_user_iov(q, rq, md, &i, GFP_ATOMIC); kfree(iov); -- 2.39.2