[PATCH] nfs4: Fix potential use after free of state in nfs4_do_reclaim.

[green@linuxhacker.ru]

From: Oleg Drokin <green@linuxhacker.ru>

Commit e8d975e73e5f ("fixing infinite OPEN loop in 4.0 stateid recovery")
introduced access to state after it was just potentially freed by
nfs4_put_open_state leading to a random data corruption somewhere.

BUG: unable to handle kernel paging request at ffff88004941ee40
IP: [<ffffffff813baf01>] nfs4_do_reclaim+0x461/0x740
PGD 3501067 PUD 3504067 PMD 6ff37067 PTE 800000004941e060
Oops: 0002 [#1] SMP DEBUG_PAGEALLOC
Modules linked in: loop rpcsec_gss_krb5 acpi_cpufreq tpm_tis joydev i2c_piix4 pcspkr tpm virtio_console nfsd ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops floppy serio_raw virtio_blk drm
CPU: 6 PID: 2161 Comm: 192.168.10.253- Not tainted 4.7.0-rc1-vm-nfs+ #112
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
task: ffff8800463dcd00 ti: ffff88003ff48000 task.ti: ffff88003ff48000
RIP: 0010:[<ffffffff813baf01>]  [<ffffffff813baf01>] nfs4_do_reclaim+0x461/0x740
RSP: 0018:ffff88003ff4bd68  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffffffff81a49900 RCX: 00000000000000e8
RDX: 00000000000000e8 RSI: ffff8800418b9930 RDI: ffff880040c96c88
RBP: ffff88003ff4bdf8 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff880040c96c98
R13: ffff88004941ee20 R14: ffff88004941ee40 R15: ffff88004941ee00
FS:  0000000000000000(0000) GS:ffff88006d000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff88004941ee40 CR3: 0000000060b0b000 CR4: 00000000000006e0
Stack:
 ffffffff813baad5 ffff8800463dcd00 ffff880000000001 ffffffff810e6b68
 ffff880043ddbc88 ffff8800418b9800 ffff8800418b98c8 ffff88004941ee48
 ffff880040c96c90 ffff880040c96c00 ffff880040c96c20 ffff880040c96c40
Call Trace:
 [<ffffffff813baad5>] ? nfs4_do_reclaim+0x35/0x740
 [<ffffffff810e6b68>] ? trace_hardirqs_on_caller+0x128/0x1b0
 [<ffffffff813bb7cd>] nfs4_run_state_manager+0x5ed/0xa40
 [<ffffffff813bb1e0>] ? nfs4_do_reclaim+0x740/0x740
 [<ffffffff813bb1e0>] ? nfs4_do_reclaim+0x740/0x740
 [<ffffffff810af0d1>] kthread+0x101/0x120
 [<ffffffff810e6b68>] ? trace_hardirqs_on_caller+0x128/0x1b0
 [<ffffffff818843af>] ret_from_fork+0x1f/0x40
 [<ffffffff810aefd0>] ? kthread_create_on_node+0x250/0x250
Code: 65 80 4c 8b b5 78 ff ff ff e8 fc 88 4c 00 48 8b 7d 88 e8 13 67 d2 ff 49 8b 47 40 a8 02 0f 84 d3 01 00 00 4c 89 ff e8 7f f9 ff ff <f0> 41 80 26 7f 48 8b 7d c8 e8 b1 84 4c 00 e9 39 fd ff ff 3d e6
RIP  [<ffffffff813baf01>] nfs4_do_reclaim+0x461/0x740
 RSP <ffff88003ff4bd68>
CR2: ffff88004941ee40

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
---
 fs/nfs/nfs4state.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index 9679f47..834b875 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -1488,9 +1488,9 @@ restart:
 					}
 					spin_unlock(&state->state_lock);
 				}
-				nfs4_put_open_state(state);
 				clear_bit(NFS_STATE_RECLAIM_NOGRACE,
 					&state->flags);
+				nfs4_put_open_state(state);
 				spin_lock(&sp->so_lock);
 				goto restart;
 			}
-- 
2.5.5