nfs: don't allow nfs_find_actor to match inodes of the wrong type

Benny Halevy reported the following oops when testing RHEL6:

<7>nfs_update_inode: inode 892950 mode changed, 0040755 to 0100644
<1>BUG: unable to handle kernel NULL pointer dereference at (null)
<1>IP: [<ffffffffa02a52c5>] nfs_closedir+0x15/0x30 [nfs]
<4>PGD 81448a067 PUD 831632067 PMD 0
<4>Oops: 0000 [#1] SMP
<4>last sysfs file: /sys/kernel/mm/redhat_transparent_hugepage/enabled
<4>CPU 6
<4>Modules linked in: fuse bonding 8021q garp ebtable_nat ebtables be2iscsi iscsi_boot_sysfs bnx2i cnic uio cxgb4i cxgb4 cxgb3i libcxgbi cxgb3 mdio ib_iser rdma_cm ib_cm iw_cm ib_sa ib_mad ib_core ib_addr iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi softdog bridge stp llc xt_physdev ipt_REJECT nf_conntrack_ipv4 nf_defrag_ipv4 xt_multiport iptable_filter ip_tables ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 xt_state nf_conntrack ip6table_filter ip6_tables ipv6 dm_round_robin dm_multipath objlayoutdriver2(U) nfs(U) lockd fscache auth_rpcgss nfs_acl sunrpc vhost_net macvtap macvlan tun kvm_intel kvm be2net igb dca ptp pps_core microcode serio_raw sg iTCO_wdt iTCO_vendor_support i7core_edac edac_core shpchp ext4 mbcache jbd2 sd_mod crc_t10dif ahci dm_mirror dm_region_hash dm_log dm_mod [last unloaded: scsi_wait_scan]
<4>
<4>Pid: 6332, comm: dd Not tainted 2.6.32-358.el6.x86_64 #1 HP ProLiant DL170e G6  /ProLiant DL170e G6
<4>RIP: 0010:[<ffffffffa02a52c5>]  [<ffffffffa02a52c5>] nfs_closedir+0x15/0x30 [nfs]
<4>RSP: 0018:ffff88081458bb98  EFLAGS: 00010292
<4>RAX: ffffffffa02a52b0 RBX: 0000000000000000 RCX: 0000000000000003
<4>RDX: ffffffffa02e45a0 RSI: ffff88081440b300 RDI: ffff88082d5f5760
<4>RBP: ffff88081458bba8 R08: 0000000000000000 R09: 0000000000000000
<4>R10: 0000000000000772 R11: 0000000000400004 R12: 0000000040000008
<4>R13: ffff88082d5f5760 R14: ffff88082d6e8800 R15: ffff88082f12d780
<4>FS:  00007f728f37e700(0000) GS:ffff8800456c0000(0000) knlGS:0000000000000000
<4>CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
<4>CR2: 0000000000000000 CR3: 0000000831279000 CR4: 00000000000007e0
<4>DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
<4>DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
<4>Process dd (pid: 6332, threadinfo ffff88081458a000, task ffff88082fa0e040)
<4>Stack:
<4> 0000000040000008 ffff88081440b300 ffff88081458bbf8 ffffffff81182745
<4><d> ffff88082d5f5760 ffff88082d6e8800 ffff88081458bbf8 ffffffffffffffea
<4><d> ffff88082f12d780 ffff88082d6e8800 ffffffffa02a50a0 ffff88082d5f5760
<4>Call Trace:
<4> [<ffffffff81182745>] __fput+0xf5/0x210
<4> [<ffffffffa02a50a0>] ? do_open+0x0/0x20 [nfs]
<4> [<ffffffff81182885>] fput+0x25/0x30
<4> [<ffffffff8117e23e>] __dentry_open+0x27e/0x360
<4> [<ffffffff811c397a>] ? inotify_d_instantiate+0x2a/0x60
<4> [<ffffffff8117e4b9>] lookup_instantiate_filp+0x69/0x90
<4> [<ffffffffa02a6679>] nfs_intent_set_file+0x59/0x90 [nfs]
<4> [<ffffffffa02a686b>] nfs_atomic_lookup+0x1bb/0x310 [nfs]
<4> [<ffffffff8118e0c2>] __lookup_hash+0x102/0x160
<4> [<ffffffff81225052>] ? selinux_inode_permission+0x72/0xb0
<4> [<ffffffff8118e76a>] lookup_hash+0x3a/0x50
<4> [<ffffffff81192a4b>] do_filp_open+0x2eb/0xdd0
<4> [<ffffffff8104757c>] ? __do_page_fault+0x1ec/0x480
<4> [<ffffffff8119f562>] ? alloc_fd+0x92/0x160
<4> [<ffffffff8117de79>] do_sys_open+0x69/0x140
<4> [<ffffffff811811f6>] ? sys_lseek+0x66/0x80
<4> [<ffffffff8117df90>] sys_open+0x20/0x30
<4> [<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
<4>Code: 65 48 8b 04 25 c8 cb 00 00 83 a8 44 e0 ff ff 01 5b 41 5c c9 c3 90 55 48 89 e5 53 48 83 ec 08 0f 1f 44 00 00 48 8b 9e a0 00 00 00 <48> 8b 3b e8 13 0c f7 ff 48 89 df e8 ab 3d ec e0 48 83 c4 08 31
<1>RIP  [<ffffffffa02a52c5>] nfs_closedir+0x15/0x30 [nfs]
<4> RSP <ffff88081458bb98>
<4>CR2: 0000000000000000

I think this is ultimately due to a bug on the server. The client had
previously found a directory dentry. It then later tried to do an atomic
open on a new (regular file) dentry. The attributes it got back had the
same filehandle as the previously found directory inode. It then tried
to put the filp because it failed the aops tests for O_DIRECT opens, and
oopsed here because the ctx was still NULL.

Obviously the root cause here is a server issue, but we can take steps
to mitigate this on the client. When nfs_fhget is called, we always know
what type of inode it is. In the event that there's a broken or
malicious server on the other end of the wire, the client can end up
crashing because the wrong ops are set on it.

Have nfs_find_actor check that the inode type is correct after checking
the fileid. The fileid check should rarely ever match, so it should only
rarely ever get to this check. In the case where we have a broken
server, we may see two different inodes with the same i_ino, but the
client should be able to cope with them without crashing.

This should fix the oops reported here:

    https://bugzilla.redhat.com/show_bug.cgi?id=913660



Reported-by: Benny Halevy <bhalevy@tonian.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>