tjh.dev / kernel
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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>

authored by

Al Viro and committed by
Linus Torvalds 137d01df fd3fc0b4

+4
+4
drivers/scsi/sg.c
··· 1753 1753 return res; 1754 1754 1755 1755 iov_iter_truncate(&i, hp->dxfer_len); 1756 + if (!iov_iter_count(&i)) { 1757 + kfree(iov); 1758 + return -EINVAL; 1759 + } 1756 1760 1757 1761 res = blk_rq_map_user_iov(q, rq, md, &i, GFP_ATOMIC); 1758 1762 kfree(iov);