st: null pointer dereference panic caused by use after kref_put by st_open
Two SLES11 SP3 servers encountered similar crashes simultaneously
following some kind of SAN/tape target issue:
...
qla2xxx [0000:81:00.0]-801c:3: Abort command issued nexus=3:0:2 -- 1 2002.
qla2xxx [0000:81:00.0]-801c:3: Abort command issued nexus=3:0:2 -- 1 2002.
qla2xxx [0000:81:00.0]-8009:3: DEVICE RESET ISSUED nexus=3:0:2 cmd=ffff882f89c2c7c0.
qla2xxx [0000:81:00.0]-800c:3: do_reset failed for cmd=ffff882f89c2c7c0.
qla2xxx [0000:81:00.0]-800f:3: DEVICE RESET FAILED: Task management failed nexus=3:0:2 cmd=ffff882f89c2c7c0.
qla2xxx [0000:81:00.0]-8009:3: TARGET RESET ISSUED nexus=3:0:2 cmd=ffff882f89c2c7c0.
qla2xxx [0000:81:00.0]-800c:3: do_reset failed for cmd=ffff882f89c2c7c0.
qla2xxx [0000:81:00.0]-800f:3: TARGET RESET FAILED: Task management failed nexus=3:0:2 cmd=ffff882f89c2c7c0.
qla2xxx [0000:81:00.0]-8012:3: BUS RESET ISSUED nexus=3:0:2.
qla2xxx [0000:81:00.0]-802b:3: BUS RESET SUCCEEDED nexus=3:0:2.
qla2xxx [0000:81:00.0]-505f:3: Link is operational (8 Gbps).
qla2xxx [0000:81:00.0]-8018:3: ADAPTER RESET ISSUED nexus=3:0:2.
qla2xxx [0000:81:00.0]-00af:3: Performing ISP error recovery - ha=ffff88bf04d18000.
rport-3:0-0: blocked FC remote port time out: removing target and saving binding
qla2xxx [0000:81:00.0]-505f:3: Link is operational (8 Gbps).
qla2xxx [0000:81:00.0]-8017:3: ADAPTER RESET SUCCEEDED nexus=3:0:2.
rport-2:0-0: blocked FC remote port time out: removing target and saving binding
sg_rq_end_io: device detached
BUG: unable to handle kernel NULL pointer dereference at 00000000000002a8
IP: [<ffffffff8133b268>] __pm_runtime_idle+0x28/0x90
PGD 7e6586f067 PUD 7e5af06067 PMD 0 [1739975.390354] Oops: 0002 [#1] SMP
CPU 0
...
Supported: No, Proprietary modules are loaded [1739975.390463]
Pid: 27965, comm: ABCD Tainted: PF X 3.0.101-0.29-default #1 HP ProLiant DL580 Gen8
RIP: 0010:[<ffffffff8133b268>] [<ffffffff8133b268>] __pm_runtime_idle+0x28/0x90
RSP: 0018:ffff8839dc1e7c68 EFLAGS: 00010202
RAX: 0000000000000000 RBX: ffff883f0592fc00 RCX: 0000000000000090
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000138
RBP: 0000000000000138 R08: 0000000000000010 R09: ffffffff81bd39d0
R10: 00000000000009c0 R11: ffffffff81025790 R12: 0000000000000001
R13: ffff883022212b80 R14: 0000000000000004 R15: ffff883022212b80
FS: 00007f8e54560720(0000) GS:ffff88407f800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00000000000002a8 CR3: 0000007e6ced6000 CR4: 00000000001407f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process ABCD (pid: 27965, threadinfo ffff8839dc1e6000, task ffff883592e0c640)
Stack:
ffff883f0592fc00 00000000fffffffa 0000000000000001 ffff883022212b80
ffff883eff772400 ffffffffa03fa309 0000000000000000 0000000000000000
ffffffffa04003a0 ffff883f063196c0 ffff887f0379a930 ffffffff8115ea1e
Call Trace:
[<ffffffffa03fa309>] st_open+0x129/0x240 [st]
[<ffffffff8115ea1e>] chrdev_open+0x13e/0x200
[<ffffffff811588a8>] __dentry_open+0x198/0x310
[<ffffffff81167d74>] do_last+0x1f4/0x800
[<ffffffff81168fe9>] path_openat+0xd9/0x420
[<ffffffff8116946c>] do_filp_open+0x4c/0xc0
[<ffffffff8115a00f>] do_sys_open+0x17f/0x250
[<ffffffff81468d92>] system_call_fastpath+0x16/0x1b
[<00007f8e4f617fd0>] 0x7f8e4f617fcf
Code: eb d3 90 48 83 ec 28 40 f6 c6 04 48 89 6c 24 08 4c 89 74 24 20 48 89 fd 48 89 1c 24 4c 89 64 24 10 41 89 f6 4c 89 6c 24 18 74 11 <f0> ff 8f 70 01 00 00 0f 94 c0 45 31 ed 84 c0 74 2b 4c 8d a5 a0
RIP [<ffffffff8133b268>] __pm_runtime_idle+0x28/0x90
RSP <ffff8839dc1e7c68>
CR2: 00000000000002a8
Analysis reveals the cause of the crash to be due to STp->device
being NULL. The pointer was NULLed via scsi_tape_put(STp) when it
calls scsi_tape_release(). In st_open() we jump to err_out after
scsi_block_when_processing_errors() completes and returns the
device as offline (sdev_state was SDEV_DEL):
1180 /* Open the device. Needs to take the BKL only because of incrementing the SCSI host
1181 module count. */
1182 static int st_open(struct inode *inode, struct file *filp)
1183 {
1184 int i, retval = (-EIO);
1185 int resumed = 0;
1186 struct scsi_tape *STp;
1187 struct st_partstat *STps;
1188 int dev = TAPE_NR(inode);
1189 char *name;
...
1217 if (scsi_autopm_get_device(STp->device) < 0) {
1218 retval = -EIO;
1219 goto err_out;
1220 }
1221 resumed = 1;
1222 if (!scsi_block_when_processing_errors(STp->device)) {
1223 retval = (-ENXIO);
1224 goto err_out;
1225 }
...
1264 err_out:
1265 normalize_buffer(STp->buffer);
1266 spin_lock(&st_use_lock);
1267 STp->in_use = 0;
1268 spin_unlock(&st_use_lock);
1269 scsi_tape_put(STp); <-- STp->device = 0 after this
1270 if (resumed)
1271 scsi_autopm_put_device(STp->device);
1272 return retval;
The ref count for the struct scsi_tape had already been reduced
to 1 when the .remove method of the st module had been called.
The kref_put() in scsi_tape_put() caused scsi_tape_release()
to be called:
0266 static void scsi_tape_put(struct scsi_tape *STp)
0267 {
0268 struct scsi_device *sdev = STp->device;
0269
0270 mutex_lock(&st_ref_mutex);
0271 kref_put(&STp->kref, scsi_tape_release); <-- calls this
0272 scsi_device_put(sdev);
0273 mutex_unlock(&st_ref_mutex);
0274 }
In scsi_tape_release() the struct scsi_device in the struct
scsi_tape gets set to NULL:
4273 static void scsi_tape_release(struct kref *kref)
4274 {
4275 struct scsi_tape *tpnt = to_scsi_tape(kref);
4276 struct gendisk *disk = tpnt->disk;
4277
4278 tpnt->device = NULL; <<<---- where the dev is nulled
4279
4280 if (tpnt->buffer) {
4281 normalize_buffer(tpnt->buffer);
4282 kfree(tpnt->buffer->reserved_pages);
4283 kfree(tpnt->buffer);
4284 }
4285
4286 disk->private_data = NULL;
4287 put_disk(disk);
4288 kfree(tpnt);
4289 return;
4290 }
Although the problem was reported on SLES11.3 the problem appears
in linux-next as well.
The crash is fixed by reordering the code so we no longer access
the struct scsi_tape after the kref_put() is done on it in st_open().
Signed-off-by: 
Shane Seymour <shane.seymour@hp.com>
Signed-off-by: 
Darren Lavender <darren.lavender@hp.com>
Reviewed-by: 
Johannes Thumshirn <jthumshirn@suse.com>
Acked-by: 
Kai Mäkisara <kai.makisara@kolumbus.fi>
Cc: stable@vger.kernel.org
Signed-off-by: 
James Bottomley <JBottomley@Odin.com>
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