2017-10-29 01:48:53 -04:00
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From f3951a3709ff50990bf3e188c27d346792103432 Mon Sep 17 00:00:00 2001
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From: Calvin Owens <calvinowens@fb.com>
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Date: Fri, 30 Oct 2015 16:57:00 -0700
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2017-11-07 17:32:46 -05:00
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Subject: sg: Fix double-free when drives detach during SG_IO
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2017-10-29 01:48:53 -04:00
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In sg_common_write(), we free the block request and return -ENODEV if
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the device is detached in the middle of the SG_IO ioctl().
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Unfortunately, sg_finish_rem_req() also tries to free srp->rq, so we
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end up freeing rq->cmd in the already free rq object, and then free
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the object itself out from under the current user.
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This ends up corrupting random memory via the list_head on the rq
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object. The most common crash trace I saw is this:
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------------[ cut here ]------------
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kernel BUG at block/blk-core.c:1420!
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Call Trace:
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[<ffffffff81281eab>] blk_put_request+0x5b/0x80
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[<ffffffffa0069e5b>] sg_finish_rem_req+0x6b/0x120 [sg]
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[<ffffffffa006bcb9>] sg_common_write.isra.14+0x459/0x5a0 [sg]
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[<ffffffff8125b328>] ? selinux_file_alloc_security+0x48/0x70
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[<ffffffffa006bf95>] sg_new_write.isra.17+0x195/0x2d0 [sg]
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[<ffffffffa006cef4>] sg_ioctl+0x644/0xdb0 [sg]
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[<ffffffff81170f80>] do_vfs_ioctl+0x90/0x520
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[<ffffffff81258967>] ? file_has_perm+0x97/0xb0
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[<ffffffff811714a1>] SyS_ioctl+0x91/0xb0
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[<ffffffff81602afb>] tracesys+0xdd/0xe2
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RIP [<ffffffff81281e04>] __blk_put_request+0x154/0x1a0
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The solution is straightforward: just set srp->rq to NULL in the
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failure branch so that sg_finish_rem_req() doesn't attempt to re-free
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it.
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Additionally, since sg_rq_end_io() will never be called on the object
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when this happens, we need to free memory backing ->cmd if it isn't
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embedded in the object itself.
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KASAN was extremely helpful in finding the root cause of this bug.
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Signed-off-by: Calvin Owens <calvinowens@fb.com>
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Acked-by: Douglas Gilbert <dgilbert@interlog.com>
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Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
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---
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drivers/scsi/sg.c | 8 +++++++-
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1 file changed, 7 insertions(+), 1 deletion(-)
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diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
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2017-11-07 17:32:46 -05:00
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index 9d7b7db..503ab8b 100644
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2017-10-29 01:48:53 -04:00
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--- a/drivers/scsi/sg.c
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+++ b/drivers/scsi/sg.c
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@@ -787,8 +787,14 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp,
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return k; /* probably out of space --> ENOMEM */
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}
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if (atomic_read(&sdp->detaching)) {
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- if (srp->bio)
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+ if (srp->bio) {
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+ if (srp->rq->cmd != srp->rq->__cmd)
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+ kfree(srp->rq->cmd);
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+
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blk_end_request_all(srp->rq, -EIO);
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+ srp->rq = NULL;
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+ }
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+
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sg_finish_rem_req(srp);
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return -ENODEV;
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}
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2017-11-07 17:32:46 -05:00
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--
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cgit v1.1
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