Patch "Fix missing sanity check in /dev/sg" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

Fix missing sanity check in /dev/sg

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fix-missing-sanity-check-in-dev-sg.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Al Viro <[email protected]>
Date: Sun, 19 Feb 2017 07:15:27 +0000
Subject: Fix missing sanity check in /dev/sg

From: Al Viro <[email protected]>

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 ]

---
 drivers/scsi/sg.c |    4 ++++
 1 file changed, 4 insertions(+)

@@ -1763,6 +1763,10 @@ sg_start_req(Sg_request *srp, unsigned c
 			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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/fix-missing-sanity-check-in-dev-sg.patch