Commit 137d01df authored by Al Viro's avatar Al Viro Committed by Linus Torvalds
Browse files

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: default avatarAl Viro <>
Reported-by: default avatarDmitry Vyukov <>
Reviewed-by: default avatarChristoph Hellwig <>
Signed-off-by: default avatarLinus Torvalds <>
parent fd3fc0b4
......@@ -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)) {
return -EINVAL;
res = blk_rq_map_user_iov(q, rq, md, &i, GFP_ATOMIC);
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