NULL dereference from nfs_destroy_server, with possible fix.

Hi,

I recently managed to get the following stack trace, though I haven't been able to reproduce it.

Dec 12 17:17:04 hp kernel: [22684.894434] BUG: unable to handle kernel NULL pointer dereference at 0000000000000310
Dec 12 17:17:04 hp kernel: [22684.894490] IP: [<ffffffff813248f9>] nlmclnt_done+0x9/0x30
Dec 12 17:17:04 hp kernel: [22684.894529] PGD 13cc5a067 PUD 13ca0a067 PMD 0 
Dec 12 17:17:04 hp kernel: [22684.894593] Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC
Dec 12 17:17:04 hp kernel: [22684.894660] Modules linked in:
Dec 12 17:17:04 hp kernel: [22684.894691] CPU 0 
Dec 12 17:17:04 hp kernel: [22684.894708] Pid: 6874, comm: ls Not tainted 3.7.0-rc1+ #323 HP ProLiant ML310 G3
Dec 12 17:17:04 hp kernel: [22684.894745] RIP: 0010:[<ffffffff813248f9>]  [<ffffffff813248f9>] nlmclnt_done+0x9/0x30
Dec 12 17:17:04 hp kernel: [22684.894783] RSP: 0018:ffff880139d59958  EFLAGS: 00010292
Dec 12 17:17:04 hp kernel: [22684.894804] RAX: 0000000000000000 RBX: ffff88013760e7f0 RCX: 0000000000000000
Dec 12 17:17:04 hp kernel: [22684.894829] RDX: 0000000000000046 RSI: 0000000000000001 RDI: 0000000000000000
Dec 12 17:17:04 hp kernel: [22684.894852] RBP: ffff880139d59968 R08: 0000000000000000 R09: 0000000000000000
Dec 12 17:17:04 hp kernel: [22684.894878] R10: 0000000000000001 R11: 0000000000000000 R12: dead000000200200
Dec 12 17:17:04 hp kernel: [22684.894900] R13: ffff88013bdfaed0 R14: dead000000200200 R15: ffff880139fde7f0
Dec 12 17:17:04 hp kernel: [22684.894924] FS:  00007f279bbf57c0(0000) GS:ffff880147c00000(0000) knlGS:0000000000000000
Dec 12 17:17:04 hp kernel: [22684.894947] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
Dec 12 17:17:04 hp kernel: [22684.894968] CR2: 0000000000000310 CR3: 0000000137ea1000 CR4: 00000000000007f0
Dec 12 17:17:04 hp kernel: [22684.894995] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
Dec 12 17:17:04 hp kernel: [22684.895017] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Dec 12 17:17:04 hp kernel: [22684.895039] Process ls (pid: 6874, threadinfo ffff880139d58000, task ffff88013bbdc050)
Dec 12 17:17:04 hp kernel: [22684.895061] Stack:
Dec 12 17:17:04 hp kernel: [22684.895079]  ffff880139d59978 ffff88013760e7f0 ffff880139d59978 ffffffff812c41ff
Dec 12 17:17:04 hp kernel: [22684.895148]  ffff880139d599b8 ffffffff812c4eab ffffffff812c4d9b ffff88013760e7f0
Dec 12 17:17:04 hp kernel: [22684.895220]  ffff88013760e7f0 ffffffffffffff8c ffff88013e3a7ef0 00000000ffffff8c
Dec 12 17:17:04 hp kernel: [22684.895287] Call Trace:
Dec 12 17:17:04 hp kernel: [22684.895312]  [<ffffffff812c41ff>] nfs_destroy_server+0x1f/0x30
Dec 12 17:17:04 hp kernel: [22684.895337]  [<ffffffff812c4eab>] nfs_free_server+0x13b/0x200
Dec 12 17:17:04 hp kernel: [22684.895362]  [<ffffffff812c4d9b>] ? nfs_free_server+0x2b/0x200
Dec 12 17:17:04 hp kernel: [22684.895386]  [<ffffffff812c511b>] nfs_clone_server+0x1ab/0x250
Dec 12 17:17:04 hp kernel: [22684.895411]  [<ffffffff812dc498>] nfs3_clone_server+0x18/0x50
Dec 12 17:17:04 hp kernel: [22684.895437]  [<ffffffff812ce202>] nfs_xdev_mount+0x82/0x120
Dec 12 17:17:04 hp kernel: [22684.895462]  [<ffffffff812ce300>] ? nfs_set_super+0x60/0x60
Dec 12 17:17:04 hp kernel: [22684.895486]  [<ffffffff812cdd60>] ? nfs_set_sb_security+0x10/0x10
Dec 12 17:17:04 hp kernel: [22684.895512]  [<ffffffff8116a3bb>] mount_fs+0x1b/0xd0
Dec 12 17:17:04 hp kernel: [22684.895545]  [<ffffffff811843bf>] vfs_kern_mount+0x6f/0x110
Dec 12 17:17:04 hp kernel: [22684.895569]  [<ffffffff812d8f62>] nfs_do_submount+0xa2/0x150
Dec 12 17:17:04 hp kernel: [22684.895593]  [<ffffffff812d908e>] nfs_submount+0x7e/0xa0
Dec 12 17:17:04 hp kernel: [22684.895617]  [<ffffffff812d917c>] nfs_d_automount+0xcc/0x1c0
Dec 12 17:17:04 hp kernel: [22684.895643]  [<ffffffff811706c0>] follow_managed+0x150/0x310
Dec 12 17:17:04 hp kernel: [22684.895668]  [<ffffffff811710e1>] lookup_fast+0x1c1/0x310
Dec 12 17:17:04 hp kernel: [22684.895693]  [<ffffffff811744ac>] do_last.isra.57+0x17c/0xc50
Dec 12 17:17:04 hp kernel: [22684.895717]  [<ffffffff811718a3>] ? inode_permission+0x13/0x50
Dec 12 17:17:04 hp kernel: [22684.895741]  [<ffffffff81171d6d>] ? link_path_walk+0x22d/0x8f0
Dec 12 17:17:04 hp kernel: [22684.895766]  [<ffffffff81175033>] path_openat.isra.58+0xb3/0x4c0
Dec 12 17:17:04 hp kernel: [22684.895791]  [<ffffffff811716db>] ? getname_flags+0x2b/0x110
Dec 12 17:17:04 hp kernel: [22684.895816]  [<ffffffff8118285f>] ? __alloc_fd+0x2f/0x130
Dec 12 17:17:04 hp kernel: [22684.895842]  [<ffffffff8117579c>] do_filp_open+0x3c/0x90
Dec 12 17:17:04 hp kernel: [22684.895866]  [<ffffffff81182909>] ? __alloc_fd+0xd9/0x130
Dec 12 17:17:04 hp kernel: [22684.895891]  [<ffffffff8116614f>] do_sys_open+0xef/0x1d0

The problem is that nfs_destroy_server is calling nlmclnt_done(NULL). This can happen if nfs_clone_server() is called on a v2/v3 mount but gets an error between

	server->destroy = source->destroy;

(which sets server->destroy to nfs_destroy_dever without setting server->nlm_host) and

	error = nfs_start_lockd(server);

(which sets both server->destroy and server->nlm_host).

If this happens then nfs_free_server() calls ->destroy() which crashes as shown.

Maybe this patch?

index 8b39a42..b6603bb 100644
@@ -617,7 +617,8 @@ static void nfs_destroy_server(struct nfs_server *server)
 {
 	if (!(server->flags & NFS_MOUNT_LOCAL_FLOCK) ||
 			!(server->flags & NFS_MOUNT_LOCAL_FCNTL))
-		nlmclnt_done(server->nlm_host);
+		if (server->nlm_host)
+			nlmclnt_done(server->nlm_host);
 }
 
 /*

Thanks,
NeilBrown

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No, you are right. nlm_host will only be non-NULL if the one of the flags
is set, so the test is pointless.

NeilBrown

index 8b39a42..5e8d24d 100644
@@ -615,8 +615,7 @@ EXPORT_SYMBOL_GPL(nfs_create_rpc_client);
  */
 static void nfs_destroy_server(struct nfs_server *server)
 {
-	if (!(server->flags & NFS_MOUNT_LOCAL_FLOCK) ||
-			!(server->flags & NFS_MOUNT_LOCAL_FCNTL))
+	if (server->nlm_host)
 		nlmclnt_done(server->nlm_host);
 }