4.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/scsi/sg.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1753,6 +1753,10 @@ 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);