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Fix missing sanity check in /dev/sg

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commit 137d01df51 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@zeniv.linux.org.uk>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Al Viro 2017-02-19 07:15:27 +00:00 committed by Greg Kroah-Hartman
parent 8107096d24
commit 65de8bfbbe
1 changed files with 4 additions and 0 deletions
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4
drivers/scsi/sg.c
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@ -1763,6 +1763,10 @@ 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);