ext3: NULL dereference in ext3_evict_inode()

This is an fsfuzzer bug.  ->s_journal is set at the end of
ext3_load_journal() but we try to use it in the error handling from
ext3_get_journal() while it's still NULL.

[  337.039041] BUG: unable to handle kernel NULL pointer dereference at 0000000000000024
[  337.040380] IP: [<ffffffff816e6539>] _raw_spin_lock+0x9/0x30
[  337.041687] PGD 0
[  337.043118] Oops: 0002 [#1] SMP
[  337.044483] CPU 3
[  337.044495] Modules linked in: ecb md4 cifs fuse kvm_intel kvm brcmsmac brcmutil crc8 cordic r8169 [last unloaded: scsi_wait_scan]
[  337.047633]
[  337.049259] Pid: 8308, comm: mount Not tainted 3.2.0-rc2-next-20111121+ #24 SAMSUNG ELECTRONICS CO., LTD. RV411/RV511/E3511/S3511    /RV411/RV511/E3511/S3511
[  337.051064] RIP: 0010:[<ffffffff816e6539>]  [<ffffffff816e6539>] _raw_spin_lock+0x9/0x30
[  337.052879] RSP: 0018:ffff8800b1d11ae8  EFLAGS: 00010282
[  337.054668] RAX: 0000000000000100 RBX: 0000000000000000 RCX: ffff8800b77c2000
[  337.056400] RDX: ffff8800a97b5c00 RSI: 0000000000000000 RDI: 0000000000000024
[  337.058099] RBP: ffff8800b1d11ae8 R08: 6000000000000000 R09: e018000000000000
[  337.059841] R10: ff67366cc2607c03 R11: 00000000110688e6 R12: 0000000000000000
[  337.061607] R13: 0000000000000000 R14: 0000000000000000 R15: ffff8800a78f06e8
[  337.063385] FS:  00007f9d95652800(0000) GS:ffff8800b7180000(0000) knlGS:0000000000000000
[  337.065110] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  337.066801] CR2: 0000000000000024 CR3: 00000000aef2c000 CR4: 00000000000006e0
[  337.068581] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  337.070321] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  337.072105] Process mount (pid: 8308, threadinfo ffff8800b1d10000, task ffff8800b1d02be0)
[  337.073800] Stack:
[  337.075487]  ffff8800b1d11b08 ffffffff811f48cf ffff88007ac9b158 0000000000000000
[  337.077255]  ffff8800b1d11b38 ffffffff8119405d ffff88007ac9b158 ffff88007ac9b250
[  337.078851]  ffffffff8181bda0 ffffffff8181bda0 ffff8800b1d11b68 ffffffff81131e31
[  337.080284] Call Trace:
[  337.081706]  [<ffffffff811f48cf>] log_start_commit+0x1f/0x40
[  337.083107]  [<ffffffff8119405d>] ext3_evict_inode+0x1fd/0x2a0
[  337.084490]  [<ffffffff81131e31>] evict+0xa1/0x1a0
[  337.085857]  [<ffffffff81132031>] iput+0x101/0x210
[  337.087220]  [<ffffffff811339d1>] iget_failed+0x21/0x30
[  337.088581]  [<ffffffff811905fc>] ext3_iget+0x15c/0x450
[  337.089936]  [<ffffffff8118b0c1>] ? ext3_rsv_window_add+0x81/0x100
[  337.091284]  [<ffffffff816df9a4>] ext3_get_journal+0x15/0xde
[  337.092641]  [<ffffffff811a2e9b>] ext3_fill_super+0xf2b/0x1c30
[  337.093991]  [<ffffffff810ddf7d>] ? register_shrinker+0x4d/0x60
[  337.095332]  [<ffffffff8111c112>] mount_bdev+0x1a2/0x1e0
[  337.096680]  [<ffffffff811a1f70>] ? ext3_setup_super+0x210/0x210
[  337.098026]  [<ffffffff8119a770>] ext3_mount+0x10/0x20
[  337.099362]  [<ffffffff8111cbee>] mount_fs+0x3e/0x1b0
[  337.100759]  [<ffffffff810eda1b>] ? __alloc_percpu+0xb/0x10
[  337.102330]  [<ffffffff81135385>] vfs_kern_mount+0x65/0xc0
[  337.103889]  [<ffffffff8113611f>] do_kern_mount+0x4f/0x100
[  337.105442]  [<ffffffff811378fc>] do_mount+0x19c/0x890
[  337.106989]  [<ffffffff810e8456>] ? memdup_user+0x46/0x90
[  337.108572]  [<ffffffff810e84f3>] ? strndup_user+0x53/0x70
[  337.110114]  [<ffffffff811383fb>] sys_mount+0x8b/0xe0
[  337.111617]  [<ffffffff816ed93b>] system_call_fastpath+0x16/0x1b
[  337.113133] Code: 38 c2 74 0f 66 0f 1f 44 00 00 f3 90 0f b6 03 38 c2 75 f7 48 83 c4 08 5b 5d c3 0f 1f 84 00 00 00 00 00 55 b8 00 01 00 00 48 89 e5 <f0> 66 0f c1 07 0f b6 d4 38 c2 74 0c 0f 1f 00 f3 90 0f b6 07 38
[  337.116588] RIP  [<ffffffff816e6539>] _raw_spin_lock+0x9/0x30
[  337.118260]  RSP <ffff8800b1d11ae8>
[  337.119998] CR2: 0000000000000024
[  337.188701] ---[ end trace c36d790becac1615 ]---

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext3/inode.c

@@ -223,8 +223,12 @@ void ext3_evict_inode (struct inode *inode)
 	 *
 	 * Note that directories do not have this problem because they don't
 	 * use page cache.
+	 *
+	 * The s_journal check handles the case when ext3_get_journal() fails
+	 * and puts the journal inode.
 	 */
 	if (inode->i_nlink && ext3_should_journal_data(inode) &&
+	    EXT3_SB(inode->i_sb)->s_journal &&
 	    (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode))) {
 		tid_t commit_tid = atomic_read(&ei->i_datasync_tid);
 		journal_t *journal = EXT3_SB(inode->i_sb)->s_journal;