Date:	Mon, 30 Dec 2013 16:55:19 +0100
From:	Jack Wang <jinpu.wang@...fitbricks.com>
To:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [BUG]NULL pointer dereference at 0000000000000008 __blkdev_put+0x17f/0x1d0

Hi,

We saw NULL pointer dereference below:

Dec 28 16:24:26 server kernel: [979193.076399] BUG: unable to handle
kernel NULL pointer dereference at 0000000000000008
Dec 28 16:24:26 server kernel: [979193.076401] IP: [<ffffffff8116952f>]
__blkdev_put+0x17f/0x1d0
Dec 28 16:24:26 server kernel: [979193.076408] PGD 4bdcaa067 PUD
4bdc43067 PMD 0
Dec 28 16:24:26 server kernel: [979193.076410] Oops: 0000 [#1] SMP
Dec 28 16:24:26 server kernel: [979193.076412] CPU 6
Dec 28 16:24:26 server kernel: [979193.076413] Modules linked in: bridge
stp llc nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables
raid1 md_mod dm_round_robin sd_mod crc_t10dif ib_srp scsi_transport_srp
scsi_tgt xt_ETHOIP6(O) x_tables vhost_net(O) macvtap macvlan tun(O)
nf_conntrack_ipv4 nf_conntrack nf_defrag_ipv4 rdma_ucm rdma_cm iw_cm
ib_addr ib_ipoib ib_cm ib_sa ib_uverbs ib_umad ib_qib mlx4_ib ib_mthca
ib_mad ib_core dm_multipath scsi_dh scsi_mod kvm_amd kvm powernow_k8
mperf psmouse crc32c_intel microcode tpm_tis tpm tpm_bios serio_raw
evdev amd64_edac_mod edac_core edac_mce_amd i2c_piix4 button processor
thermal_sys mlx4_core
Dec 28 16:24:26 server kernel: [979193.076440]
Dec 28 16:24:26 server kernel: [979193.076442] Pid: 56544, comm:
multipath Tainted: G           O 3.4.71-3-pserver #1 Supermicro BHQGE/BHQGE
Dec 28 16:24:26 server kernel: [979193.076445] RIP:
0010:[<ffffffff8116952f>]  [<ffffffff8116952f>] __blkdev_put+0x17f/0x1d0
Dec 28 16:24:26 server kernel: [979193.076448] RSP:
0018:ffff882802f4beb8  EFLAGS: 00010246
Dec 28 16:24:26 server kernel: [979193.076449] RAX: 0000000000000000
RBX: ffff881ff78b0d00 RCX: 0000000000000001
Dec 28 16:24:26 server kernel: [979193.076451] RDX: 0000000000000000
RSI: 000000000000001d RDI: ffff881ff78b0d18
Dec 28 16:24:26 server kernel: [979193.076452] RBP: 0000000000000000
R08: 0000000000000000 R09: 0000000000000000
Dec 28 16:24:26 server kernel: [979193.076453] R10: 0000000000000000
R11: 0000000000000246 R12: 000000000000001d
Dec 28 16:24:26 server kernel: [979193.076455] R13: ffff881ff78b0d18
R14: ffff8807f9e7f400 R15: ffff8804a8d77710
Dec 28 16:24:26 server kernel: [979193.076457] FS:
00007ff8c80fe7a0(0000) GS:ffff880807d80000(0000) knlGS:0000000000000000
Dec 28 16:24:26 server kernel: [979193.076458] CS:  0010 DS: 0000 ES:
0000 CR0: 0000000080050033
Dec 28 16:24:26 server kernel: [979193.076460] CR2: 0000000000000008
CR3: 000000064765f000 CR4: 00000000000407e0
Dec 28 16:24:26 server kernel: [979193.076461] DR0: 0000000000000000
DR1: 0000000000000000 DR2: 0000000000000000
Dec 28 16:24:26 server kernel: [979193.076463] DR3: 0000000000000000
DR6: 00000000ffff0ff0 DR7: 0000000000000400
Dec 28 16:24:26 server kernel: [979193.076464] Process multipath (pid:
56544, threadinfo ffff882802f4a000, task ffff8828020106d0)
Dec 28 16:24:26 server kernel: [979193.076466] Stack:
Dec 28 16:24:26 server kernel: [979193.076466]  0000000000000000
0000000000000000 ffff880803cf2580 ffff8804a8d77700
Dec 28 16:24:26 server kernel: [979193.076468]  0000000000000010
ffff88100363eff0 ffff881004609b00 ffff882003c20020
Dec 28 16:24:26 server kernel: [979193.076470]  ffff8804a8d77710
ffffffff81136bad 00007fffbdc8f420 ffff8804a8d77700
Dec 28 16:24:26 server kernel: [979193.076472] Call Trace:
Dec 28 16:24:26 server kernel: [979193.076477]  [<ffffffff81136bad>] ?
fput+0xdd/0x270
Dec 28 16:24:26 server kernel: [979193.076479]  [<ffffffff81132f0c>] ?
filp_close+0x5c/0x90
Dec 28 16:24:26 server kernel: [979193.076481]  [<ffffffff81132fb1>] ?
sys_close+0x71/0xc0
Dec 28 16:24:26 server kernel: [979193.076484]  [<ffffffff816801b9>] ?
system_call_fastpath+0x16/0x1b
Dec 28 16:24:26 server kernel: [979193.076486] Code: 8b 5c 24 18 48 8b
6c 24 20 4c 8b 64 24 28 4c 8b 6c 24 30 4c 8b 74 24 38 4c 8b 7c 24 40 48
83 c4 48 c3 66 90 49 8b 86 48 03 00 00 <48> 8b 40 08 48 85 c0 0f 84 fc
fe ff ff 44 89 e6 4c 89 f7 ff d0
Dec 28 16:24:26 server kernel: [979193.076500] RIP  [<ffffffff8116952f>]
__blkdev_put+0x17f/0x1d0
Dec 28 16:24:26 server kernel: [979193.076503]  RSP <ffff882802f4beb8>
Dec 28 16:24:26 server kernel: [979193.076504] CR2: 0000000000000008
Dec 28 16:24:26 server kernel: [979193.077599] ---[ end trace
23f39da823d257f9 ]---

disassamble results show:
1465	static int __blkdev_put(struct block_device *bdev, fmode_t mode,
int for_part)
1466	{
   0xffffffff81162d10 <+0>:	sub    $0x48,%rsp
   0xffffffff81162d14 <+4>:	mov    %r13,0x30(%rsp)
   0xffffffff81162d1d <+13>:	mov    %rbx,0x18(%rsp)
   0xffffffff81162d22 <+18>:	mov    %rbp,0x20(%rsp)
   0xffffffff81162d27 <+23>:	mov    %r12,0x28(%rsp)
   0xffffffff81162d2c <+28>:	mov    %edx,%ebp
   0xffffffff81162d2e <+30>:	mov    %r14,0x38(%rsp)
   0xffffffff81162d33 <+35>:	mov    %r15,0x40(%rsp)
   0xffffffff81162d38 <+40>:	mov    %rdi,%rbx
   0xffffffff81162d45 <+53>:	mov    %esi,%r12d

1467		int ret = 0;
   0xffffffff81162d8e <+126>:	xor    %ebp,%ebp

1468		struct gendisk *disk = bdev->bd_disk;
   0xffffffff81162d3b <+43>:	mov    0x90(%rdi),%r14

1469		struct block_device *victim = NULL;
1470	
1471		mutex_lock_nested(&bdev->bd_mutex, for_part);
   0xffffffff81162d19 <+9>:	lea    0x18(%rdi),%r13
---Type <return> to continue, or q <return> to quit---
   0xffffffff81162d42 <+50>:	mov    %r13,%rdi
   0xffffffff81162d48 <+56>:	callq  0xffffffff8166ece0 <mutex_lock>

1472		if (for_part)
   0xffffffff81162d4d <+61>:	test   %ebp,%ebp
   0xffffffff81162d4f <+63>:	je     0xffffffff81162d57 <__blkdev_put+71>

1473			bdev->bd_part_count--;
   0xffffffff81162d51 <+65>:	decl   0x88(%rbx)

1474	
1475		if (!--bdev->bd_openers) {
   0xffffffff81162d57 <+71>:	mov    0x4(%rbx),%eax
   0xffffffff81162d5a <+74>:	dec    %eax
   0xffffffff81162d5c <+76>:	test   %eax,%eax
   0xffffffff81162d5e <+78>:	mov    %eax,0x4(%rbx)
   0xffffffff81162d61 <+81>:	jne    0xffffffff81162d8e <__blkdev_put+126>

1476			WARN_ON_ONCE(bdev->bd_holders);
   0xffffffff81162d63 <+83>:	mov    0x58(%rbx),%edx
   0xffffffff81162d66 <+86>:	test   %edx,%edx
   0xffffffff81162d68 <+88>:	jne    0xffffffff81162e9b <__blkdev_put+395>
   0xffffffff81162e9b <+395>:	cmpb   $0x1,0x936b1e(%rip)        #
0xffffffff81a999c0 <__warned.29603>
   0xffffffff81162ea2 <+402>:	je     0xffffffff81162d6e <__blkdev_put+94>
   0xffffffff81162ea8 <+408>:	mov    $0x5c4,%esi
   0xffffffff81162ead <+413>:	mov    $0xffffffff8193f5a7,%rdi
   0xffffffff81162eb4 <+420>:	callq  0xffffffff81036ee0 <warn_slowpath_null>
   0xffffffff81162eb9 <+425>:	movb   $0x1,0x936b00(%rip)        #
0xffffffff81a999c0 <__warned.29603>
   0xffffffff81162ec0 <+432>:	jmpq   0xffffffff81162d6e <__blkdev_put+94>
   0xffffffff81162ec5:	data32 nopw %cs:0x0(%rax,%rax,1)

1484		}
1485		if (bdev->bd_contains == bdev) {
   0xffffffff81162d90 <+128>:	cmp    %rbx,0x70(%rbx)
   0xffffffff81162d94 <+132>:	je     0xffffffff81162e78 <__blkdev_put+360>

1486			if (disk->fops->release)
---Type <return> to continue, or q <return> to quit---
   0xffffffff81162e78 <+360>:	mov    0x348(%r14),%raxat
   0xffffffff81162e7f <+367>:	mov    0x8(%rax),%rax
   0xffffffff81162e83 <+371>:	test   %rax,%rax
   0xffffffff81162e86 <+374>:	je     0xffffffff81162d9a <__blkdev_put+138>

1487				ret = disk->fops->release(disk, mode);
   0xffffffff81162e8c <+380>:	mov    %r12d,%esi
   0xffffffff81162e8f <+383>:	mov    %r14,%rdi
   0xffffffff81162e92 <+386>:	callq  *%rax
   0xffffffff81162e94 <+388>:	mov    %eax,%ebp
   0xffffffff81162e96 <+390>:	jmpq   0xffffffff81162d9a <__blkdev_put+138>
snip

Bug happened at line 1486, looks disk->fops is NULL here for some
reason, is it reasonable to add a check like:

if (disk->fops)
	if (disk->fops->release)
		ret = disk->fops->release(disk, mode);


Happy New Year and Best regards:)
Jack
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