linux-kernel - [PATCH 3.16 286/306] sg: Fix double-free when drives detach during SG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <lsq.1487198501.37485066@decadent.org.uk>
Date:   Wed, 15 Feb 2017 22:41:41 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Douglas Gilbert" <dgilbert@...erlog.com>,
        "Calvin Owens" <calvinowens@...com>
Subject: [PATCH 3.16 286/306] sg: Fix double-free when drives detach
 during SG_IO

3.16.40-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Calvin Owens <calvinowens@...com>

commit f3951a3709ff50990bf3e188c27d346792103432 upstream.

In sg_common_write(), we free the block request and return -ENODEV if
the device is detached in the middle of the SG_IO ioctl().

Unfortunately, sg_finish_rem_req() also tries to free srp->rq, so we
end up freeing rq->cmd in the already free rq object, and then free
the object itself out from under the current user.

This ends up corrupting random memory via the list_head on the rq
object. The most common crash trace I saw is this:

  ------------[ cut here ]------------
  kernel BUG at block/blk-core.c:1420!
  Call Trace:
  [<ffffffff81281eab>] blk_put_request+0x5b/0x80
  [<ffffffffa0069e5b>] sg_finish_rem_req+0x6b/0x120 [sg]
  [<ffffffffa006bcb9>] sg_common_write.isra.14+0x459/0x5a0 [sg]
  [<ffffffff8125b328>] ? selinux_file_alloc_security+0x48/0x70
  [<ffffffffa006bf95>] sg_new_write.isra.17+0x195/0x2d0 [sg]
  [<ffffffffa006cef4>] sg_ioctl+0x644/0xdb0 [sg]
  [<ffffffff81170f80>] do_vfs_ioctl+0x90/0x520
  [<ffffffff81258967>] ? file_has_perm+0x97/0xb0
  [<ffffffff811714a1>] SyS_ioctl+0x91/0xb0
  [<ffffffff81602afb>] tracesys+0xdd/0xe2
    RIP [<ffffffff81281e04>] __blk_put_request+0x154/0x1a0

The solution is straightforward: just set srp->rq to NULL in the
failure branch so that sg_finish_rem_req() doesn't attempt to re-free
it.

Additionally, since sg_rq_end_io() will never be called on the object
when this happens, we need to free memory backing ->cmd if it isn't
embedded in the object itself.

KASAN was extremely helpful in finding the root cause of this bug.

Signed-off-by: Calvin Owens <calvinowens@...com>
Acked-by: Douglas Gilbert <dgilbert@...erlog.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
[bwh: Backported to 3.16:
 - sg_finish_rem_req() would not free srp->rq->cmd so don't do it here either
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/scsi/sg.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -766,8 +766,11 @@ sg_common_write(Sg_fd * sfp, Sg_request
 		return k;	/* probably out of space --> ENOMEM */
 	}
 	if (sdp->detached) {
-		if (srp->bio)
+		if (srp->bio) {
 			blk_end_request_all(srp->rq, -EIO);
+			srp->rq = NULL;
+		}
+
 		sg_finish_rem_req(srp);
 		return -ENODEV;
 	}