scsi: don't BUG_ON() empty DMA transfers

commit fd3fc0b4d7305fa7246622dcc0dec69c42443f45 upstream.

Don't crash the machine just because of an empty transfer. Use WARN_ON()
combined with returning an error.

Found by Dmitry Vyukov and syzkaller.

[ Changed to "WARN_ON_ONCE()". Al has a patch that should fix the root
  cause, but a BUG_ON() is not acceptable in any case, and a WARN_ON()
  might still be a cause of excessive log spamming.

  NOTE! If this warning ever triggers, we may end up leaking resources,
  since this doesn't bother to try to clean the command up. So this
  WARN_ON_ONCE() triggering does imply real problems. But BUG_ON() is
  much worse.

  People really need to stop using BUG_ON() for "this shouldn't ever
  happen". It makes pretty much any bug worse.     - Linus ]

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: James Bottomley <jejb@linux.vnet.ibm.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index a483c979b1633fbc8c61234d317611c67076efaa..f3f2dc86fda79c084d805de0fff556c778abdb02 100644 (file)
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1027,7 +1027,8 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
        struct request *rq = cmd->request;
        int error;
 
-       BUG_ON(!rq->nr_phys_segments);
+       if (WARN_ON_ONCE(!rq->nr_phys_segments))
+               return -EINVAL;
 
        error = scsi_init_sgtable(rq, &cmd->sdb, gfp_mask);
        if (error)