linux-kernel - [ 17/73] [SCSI] Fix NULL dereferences in scsi_cmd_to

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Message-Id: <20120731044313.980351051@decadent.org.uk>
Date:	Tue, 31 Jul 2012 05:43:27 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Mark Rustad <mark.d.rustad@...el.com>,
	Marcus Dennis <marcusx.e.dennis@...el.com>,
	James Bottomley <JBottomley@...allels.com>
Subject: [ 17/73] [SCSI] Fix NULL dereferences in scsi_cmd_to_driver

3.2-stable review patch.  If anyone has any objections, please let me know.

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

From: Mark Rustad <mark.d.rustad@...el.com>

commit 222a806af830fda34ad1f6bc991cd226916de060 upstream.

Avoid crashing if the private_data pointer happens to be NULL. This has
been seen sometimes when a host reset happens, notably when there are
many LUNs:

host3: Assigned Port ID 0c1601
scsi host3: libfc: Host reset succeeded on port (0c1601)
BUG: unable to handle kernel NULL pointer dereference at 0000000000000350
IP: [<ffffffff81352bb8>] scsi_send_eh_cmnd+0x58/0x3a0
<snip>
Process scsi_eh_3 (pid: 4144, threadinfo ffff88030920c000, task ffff880326b160c0)
Stack:
 000000010372e6ba 0000000000000282 000027100920dca0 ffffffffa0038ee0
 0000000000000000 0000000000030003 ffff88030920dc80 ffff88030920dc80
 00000002000e0000 0000000a00004000 ffff8803242f7760 ffff88031326ed80
Call Trace:
 [<ffffffff8105b590>] ? lock_timer_base+0x70/0x70
 [<ffffffff81352fbe>] scsi_eh_tur+0x3e/0xc0
 [<ffffffff81353a36>] scsi_eh_test_devices+0x76/0x170
 [<ffffffff81354125>] scsi_eh_host_reset+0x85/0x160
 [<ffffffff81354291>] scsi_eh_ready_devs+0x91/0x110
 [<ffffffff813543fd>] scsi_unjam_host+0xed/0x1f0
 [<ffffffff813546a8>] scsi_error_handler+0x1a8/0x200
 [<ffffffff81354500>] ? scsi_unjam_host+0x1f0/0x1f0
 [<ffffffff8106ec3e>] kthread+0x9e/0xb0
 [<ffffffff81509264>] kernel_thread_helper+0x4/0x10
 [<ffffffff8106eba0>] ? kthread_freezable_should_stop+0x70/0x70
 [<ffffffff81509260>] ? gs_change+0x13/0x13
Code: 25 28 00 00 00 48 89 45 c8 31 c0 48 8b 87 80 00 00 00 48 8d b5 60 ff ff ff 89 d1 48 89 fb 41 89 d6 4c 89 fa 48 8b 80 b8 00 00 00
 <48> 8b 80 50 03 00 00 48 8b 00 48 89 85 38 ff ff ff 48 8b 07 4c
RIP  [<ffffffff81352bb8>] scsi_send_eh_cmnd+0x58/0x3a0
 RSP <ffff88030920dc50>
CR2: 0000000000000350


Signed-off-by: Mark Rustad <mark.d.rustad@...el.com>
Tested-by: Marcus Dennis <marcusx.e.dennis@...el.com>
Signed-off-by: James Bottomley <JBottomley@...allels.com>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -785,7 +785,13 @@ static void scsi_done(struct scsi_cmnd *
 /* Move this to a header if it becomes more generally useful */
 static struct scsi_driver *scsi_cmd_to_driver(struct scsi_cmnd *cmd)
 {
-	return *(struct scsi_driver **)cmd->request->rq_disk->private_data;
+	struct scsi_driver **sdp;
+
+	sdp = (struct scsi_driver **)cmd->request->rq_disk->private_data;
+	if (!sdp)
+		return NULL;
+
+	return *sdp;
 }
 
 /**


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