nfs/filelayout: fix NULL pointer dereference in fl_pnfs_update_layout()

Calling pnfs_put_lset on an IS_ERR pointer results in a NULL pointer
dereference like the one below. At the same time the check of retvalue
of filelayout_check_deviceid() sets lseg to error, but does not free it
before that.

[ 3000.636161] BUG: unable to handle kernel NULL pointer dereference at 000000000000003c
[ 3000.636970] IP: pnfs_put_lseg+0x29/0x100 [nfsv4]
[ 3000.637420] PGD 4f23b067
[ 3000.637421] PUD 4a0f4067
[ 3000.637679] PMD 0
[ 3000.637937]
[ 3000.638287] Oops: 0000 [#1] SMP
[ 3000.638591] Modules linked in: nfs_layout_nfsv41_files nfsv3 nfnetlink_queue nfnetlink_log nfnetlink bluetooth rfkill rpcsec_gss_krb5 nfsv4 nfs fscache binfmt_misc arc4 md4 nls_utf8 cifs ccm dns_resolver rpcrdma ib_isert iscsi_target_mod ib_iser rdma_cm iw_cm libiscsi scsi_transport_iscsi ib_srpt target_core_mod ib_srp scsi_transport_srp ib_ipoib ib_ucm ib_uverbs ib_umad ib_cm ib_core nls_koi8_u nls_cp932 ts_kmp nf_conntrack_ipv4 nf_defrag_ipv4 nf_conntrack crct10dif_pclmul crc32_pclmul ghash_clmulni_intel pcspkr virtio_balloon ppdev virtio_rng parport_pc i2c_piix4 parport acpi_cpufreq nfsd auth_rpcgss nfs_acl lockd grace sunrpc xfs libcrc32c ata_generic pata_acpi virtio_blk virtio_net cirrus drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops crc32c_intel ata_piix ttm libata drm serio_raw
[ 3000.645245]  i2c_core virtio_pci virtio_ring virtio floppy dm_mirror dm_region_hash dm_log dm_mod [last unloaded: xt_u32]
[ 3000.646360] CPU: 1 PID: 26402 Comm: date Not tainted 4.11.0-rc7.1.el7.test.x86_64 #1
[ 3000.647092] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
[ 3000.647638] task: ffff8800415ada00 task.stack: ffffc90000ff0000
[ 3000.648207] RIP: 0010:pnfs_put_lseg+0x29/0x100 [nfsv4]
[ 3000.648696] RSP: 0018:ffffc90000ff39b8 EFLAGS: 00010246
[ 3000.649193] RAX: 0000000000000000 RBX: fffffffffffffff4 RCX: 00000000000d43be
[ 3000.649859] RDX: 00000000000d43bd RSI: 0000000000000000 RDI: fffffffffffffff4
[ 3000.650530] RBP: ffffc90000ff39d8 R08: 000000000001e320 R09: ffffffffa05c35ce
[ 3000.651203] R10: ffff88007fd1e320 R11: ffffea0001283d80 R12: 0000000001400040
[ 3000.651875] R13: ffff88004f77d9f0 R14: ffffc90000ff3cd8 R15: ffff8800417ade00
[ 3000.652546] FS:  00007fac4d5cd740(0000) GS:ffff88007fd00000(0000) knlGS:0000000000000000
[ 3000.653304] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 3000.653849] CR2: 000000000000003c CR3: 000000004f080000 CR4: 00000000000406e0
[ 3000.654527] Call Trace:
[ 3000.654771]  fl_pnfs_update_layout.constprop.20+0x10c/0x150 [nfs_layout_nfsv41_files]
[ 3000.655505]  filelayout_pg_init_write+0x21d/0x270 [nfs_layout_nfsv41_files]
[ 3000.656195]  __nfs_pageio_add_request+0x11c/0x490 [nfs]
[ 3000.656698]  nfs_pageio_add_request+0xac/0x260 [nfs]
[ 3000.657180]  nfs_do_writepage+0x109/0x2e0 [nfs]
[ 3000.657616]  nfs_writepages_callback+0x16/0x30 [nfs]
[ 3000.658096]  write_cache_pages+0x26f/0x510
[ 3000.658495]  ? nfs_do_writepage+0x2e0/0x2e0 [nfs]
[ 3000.658946]  ? _raw_spin_unlock_bh+0x1e/0x20
[ 3000.659357]  ? wb_wakeup_delayed+0x5f/0x70
[ 3000.659748]  ? __mark_inode_dirty+0x2eb/0x360
[ 3000.660170]  nfs_writepages+0x84/0xd0 [nfs]
[ 3000.660575]  ? nfs_updatepage+0x571/0xb70 [nfs]
[ 3000.661012]  do_writepages+0x1e/0x30
[ 3000.661358]  __filemap_fdatawrite_range+0xc6/0x100
[ 3000.661819]  filemap_write_and_wait_range+0x41/0x90
[ 3000.662292]  nfs_file_fsync+0x34/0x1f0 [nfs]
[ 3000.662704]  vfs_fsync_range+0x3d/0xb0
[ 3000.663065]  vfs_fsync+0x1c/0x20
[ 3000.663385]  nfs4_file_flush+0x57/0x80 [nfsv4]
[ 3000.663813]  filp_close+0x2f/0x70
[ 3000.664132]  __close_fd+0x9a/0xc0
[ 3000.664453]  SyS_close+0x23/0x50
[ 3000.664785]  do_syscall_64+0x67/0x180
[ 3000.665162]  entry_SYSCALL64_slow_path+0x25/0x25
[ 3000.665600] RIP: 0033:0x7fac4d0e1e90
[ 3000.665946] RSP: 002b:00007ffd54e90c88 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
[ 3000.666679] RAX: ffffffffffffffda RBX: 00007fac4d3b5400 RCX: 00007fac4d0e1e90
[ 3000.667349] RDX: 0000000000000000 RSI: 00007fac4d5d9000 RDI: 0000000000000001
[ 3000.668031] RBP: 0000000000000000 R08: 00007fac4d3b6a00 R09: 00007fac4d5cd740
[ 3000.668709] R10: 00007ffd54e909e0 R11: 0000000000000246 R12: 0000000000000000
[ 3000.669385] R13: 00007fac4d3b5e80 R14: 0000000000000000 R15: 0000000000000000
[ 3000.670061] Code: 00 00 66 66 66 66 90 55 48 85 ff 48 89 e5 41 56 41 55 41 54 53 48 89 fb 0f 84 97 00 00 00 f6 05 16 8f bc ff 10 0f 85 a6 00 00 00 <4c> 8b 63 48 48 8d 7b 38 49 8b 84 24 90 00 00 00 4c 8d a8 88 00
[ 3000.671831] RIP: pnfs_put_lseg+0x29/0x100 [nfsv4] RSP: ffffc90000ff39b8
[ 3000.672462] CR2: 000000000000003c

Signed-off-by: Artem Savkov <asavkov@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/filelayout/filelayout.c

@@ -921,11 +921,11 @@ fl_pnfs_update_layout(struct inode *ino,
 	fl = FILELAYOUT_LSEG(lseg);
 
 	status = filelayout_check_deviceid(lo, fl, gfp_flags);
-	if (status)
+	if (status) {
-		lseg = ERR_PTR(status);
-out:
-	if (IS_ERR(lseg))
 		pnfs_put_lseg(lseg);
+		lseg = ERR_PTR(status);
+	}
+out:
 	return lseg;
 }