Patch "scsi: zfcp: fix use-after-"free" in FC ingress path after TMF" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

scsi: zfcp: fix use-after-"free" in FC ingress path after TMF

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
scsi-zfcp-fix-use-after-free-in-fc-ingress-path-after-tmf.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Benjamin Block <[email protected]>
Date: Fri, 9 Dec 2016 17:16:31 +0100
Subject: scsi: zfcp: fix use-after-"free" in FC ingress path after TMF

From: Benjamin Block <[email protected]>

commit dac37e15b7d511e026a9313c8c46794c144103cd upstream.

When SCSI EH invokes zFCP's callbacks for eh_device_reset_handler() and eh_target_reset_handler(), it expects us to relent the ownership over the given scsi_cmnd and all other scsi_cmnds within the same scope - LUN or target - when returning with SUCCESS from the callback ('release' them). SCSI EH can then reuse those commands.

We did not follow this rule to release commands upon SUCCESS; and if later a reply arrived for one of those supposed to be released commands, we would still make use of the scsi_cmnd in our ingress tasklet. This will at least result in undefined behavior or a kernel panic because of a wrong kernel pointer dereference.

To fix this, we NULLify all pointers to scsi_cmnds (struct zfcp_fsf_req *)->data in the matching scope if a TMF was successful. This is done under the locks (struct zfcp_adapter *)->abort_lock and (struct zfcp_reqlist *)->lock to prevent the requests from being removed from the request-hashtable, and the ingress tasklet from making use of the scsi_cmnd-pointer in zfcp_fsf_fcp_cmnd_handler().

For cases where a reply arrives during SCSI EH, but before we get a chance to NULLify the pointer - but before we return from the callback -, we assume that the code is protected from races via the CAS operation in blk_complete_request() that is called in scsi_done().

The following stacktrace shows an example for a crash resulting from the previous behavior:

Unable to handle kernel pointer dereference at virtual kernel address fffffee17a672000
Oops: 0038 [#1] SMP
CPU: 2 PID: 0 Comm: swapper/2 Not tainted
task: 00000003f7ff5be0 ti: 00000003f3d38000 task.ti: 00000003f3d38000
Krnl PSW : 0404d00180000000 00000000001156b0 (smp_vcpu_scheduled+0x18/0x40)
           R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 EA:3
Krnl GPRS: 000000200000007e 0000000000000000 fffffee17a671fd8 0000000300000015
           ffffffff80000000 00000000005dfde8 07000003f7f80e00 000000004fa4e800
           000000036ce8d8f8 000000036ce8d9c0 00000003ece8fe00 ffffffff969c9e93
           00000003fffffffd 000000036ce8da10 00000000003bf134 00000003f3b07918
Krnl Code: 00000000001156a2: a7190000        lghi    %r1,0
           00000000001156a6: a7380015        lhi    %r3,21
          #00000000001156aa: e32050000008    ag    %r2,0(%r5)
          >00000000001156b0: 482022b0        lh    %r2,688(%r2)
           00000000001156b4: ae123000        sigp    %r1,%r2,0(%r3)
           00000000001156b8: b2220020        ipm    %r2
           00000000001156bc: 8820001c        srl    %r2,28
           00000000001156c0: c02700000001    xilf    %r2,1
Call Trace:
([<0000000000000000>] 0x0)
 [<000003ff807bdb8e>] zfcp_fsf_fcp_cmnd_handler+0x3de/0x490 [zfcp]
 [<000003ff807be30a>] zfcp_fsf_req_complete+0x252/0x800 [zfcp]
 [<000003ff807c0a48>] zfcp_fsf_reqid_check+0xe8/0x190 [zfcp]
 [<000003ff807c194e>] zfcp_qdio_int_resp+0x66/0x188 [zfcp]
 [<000003ff80440c64>] qdio_kick_handler+0xdc/0x310 [qdio]
 [<000003ff804463d0>] __tiqdio_inbound_processing+0xf8/0xcd8 [qdio]
 [<0000000000141fd4>] tasklet_action+0x9c/0x170
 [<0000000000141550>] __do_softirq+0xe8/0x258
 [<000000000010ce0a>] do_softirq+0xba/0xc0
 [<000000000014187c>] irq_exit+0xc4/0xe8
 [<000000000046b526>] do_IRQ+0x146/0x1d8
 [<00000000005d6a3c>] io_return+0x0/0x8
 [<00000000005d6422>] vtime_stop_cpu+0x4a/0xa0
([<0000000000000000>] 0x0)
 [<0000000000103d8a>] arch_cpu_idle+0xa2/0xb0
 [<0000000000197f94>] cpu_startup_entry+0x13c/0x1f8
 [<0000000000114782>] smp_start_secondary+0xda/0xe8
 [<00000000005d6efe>] restart_int_handler+0x56/0x6c
 [<0000000000000000>] 0x0

Last Breaking-Event-Address:
[<00000000003bf12e>] arch_spin_lock_wait+0x56/0xb0

---
 drivers/s390/scsi/zfcp_dbf.h     |   11 +++++++
 drivers/s390/scsi/zfcp_reqlist.h |   30 +++++++++++++++++++-
 drivers/s390/scsi/zfcp_scsi.c    |   57 +++++++++++++++++++++++++++++++++++++--
 3 files changed, 95 insertions(+), 3 deletions(-)

@@ -388,4 +388,15 @@ void zfcp_dbf_scsi_devreset(char *tag, s
 	_zfcp_dbf_scsi(tmp_tag, 1, scmnd, NULL);
 }
 
+/**
+ * zfcp_dbf_scsi_nullcmnd() - trace NULLify of SCSI command in dev/tgt-reset.
+ * @scmnd: SCSI command that was NULLified.
+ * @fsf_req: request that owned @scmnd.
+ */
+static inline void zfcp_dbf_scsi_nullcmnd(struct scsi_cmnd *scmnd,
+					  struct zfcp_fsf_req *fsf_req)
+{
+	_zfcp_dbf_scsi("scfc__1", 3, scmnd, fsf_req);
+}
+
 #endif /* ZFCP_DBF_H */

@@ -4,7 +4,7 @@
  * Data structure and helper functions for tracking pending FSF
  * requests.
  *
- * Copyright IBM Corp. 2009
+ * Copyright IBM Corp. 2009, 2016
  */
 
 #ifndef ZFCP_REQLIST_H

@@ -180,4 +180,32 @@ static inline void zfcp_reqlist_move(str
 	spin_unlock_irqrestore(&rl->lock, flags);
 }
 
+/**
+ * zfcp_reqlist_apply_for_all() - apply a function to every request.
+ * @rl: the requestlist that contains the target requests.
+ * @f: the function to apply to each request; the first parameter of the
+ *     function will be the target-request; the second parameter is the same
+ *     pointer as given with the argument @data.
+ * @data: freely chosen argument; passed through to @f as second parameter.
+ *
+ * Uses :c:macro:`list_for_each_entry` to iterate over the lists in the hash-
+ * table (not a 'safe' variant, so don't modify the list).
+ *
+ * Holds @rl->lock over the entire request-iteration.
+ */
+static inline void
+zfcp_reqlist_apply_for_all(struct zfcp_reqlist *rl,
+			   void (*f)(struct zfcp_fsf_req *, void *), void *data)
+{
+	struct zfcp_fsf_req *req;
+	unsigned long flags;
+	unsigned int i;
+
+	spin_lock_irqsave(&rl->lock, flags);
+	for (i = 0; i < ZFCP_REQ_LIST_BUCKETS; i++)
+		list_for_each_entry(req, &rl->buckets[i], list)
+			f(req, data);
+	spin_unlock_irqrestore(&rl->lock, flags);
+}
+
 #endif /* ZFCP_REQLIST_H */

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/scsi-zfcp-do-not-trace-pure-benign-residual-hba-responses-at-default-level.patch queue-4.4/scsi-zfcp-fix-rport-unblock-race-with-lun-recovery.patch queue-4.4/scsi-zfcp-fix-use-after-free-in-fc-ingress-path-after-tmf.patch