CVE-2024-36939: nfs: Handle error of rpc_proc_register() in nfs_net_init().

In the Linux kernel, the following vulnerability has been resolved:

nfs: Handle error of rpcprocregister() in nfsnetinit().

syzkaller reported a warning [0] triggered while destroying immature netns.

rpcprocregister() was called in initnfsfs(), but its error has been ignored since at least the initial commit 1da177e4c3f4 ("Linux-2.6.12-rc2").

Recently, commit d47151b79e32 ("nfs: expose /proc/net/sunrpc/nfs in net namespaces") converted the procfs to per-netns and made the problem more visible.

Even when rpcprocregister() fails, nfsnetinit() could succeed, and thus nfsnetexit() will be called while destroying the netns.

Then, removeprocentry() will be called for non-existing proc directory and trigger the warning below.

Let's handle the error of rpcprocregister() properly in nfsnetinit().

[0]: name 'nfs' WARNING: CPU: 1 PID: 1710 at fs/proc/generic.c:711 removeprocentry+0x1bb/0x2d0 fs/proc/generic.c:711 Modules linked in: CPU: 1 PID: 1710 Comm: syz-executor.2 Not tainted 6.8.0-12822-gcd51db110a7e #12 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014 RIP: 0010:removeprocentry+0x1bb/0x2d0 fs/proc/generic.c:711 Code: 41 5d 41 5e c3 e8 85 09 b5 ff 48 c7 c7 88 58 64 86 e8 09 0e 71 02 e8 74 09 b5 ff 4c 89 e6 48 c7 c7 de 1b 80 84 e8 c5 ad 97 ff <0f> 0b eb b1 e8 5c 09 b5 ff 48 c7 c7 88 58 64 86 e8 e0 0d 71 02 eb RSP: 0018:ffffc9000c6d7ce0 EFLAGS: 00010286 RAX: 0000000000000000 RBX: ffff8880422b8b00 RCX: ffffffff8110503c RDX: ffff888030652f00 RSI: ffffffff81105045 RDI: 0000000000000001 RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000001 R11: ffffffff81bb62cb R12: ffffffff84807ffc R13: ffff88804ad6fcc0 R14: ffffffff84807ffc R15: ffffffff85741ff8 FS: 00007f30cfba8640(0000) GS:ffff88807dd00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007ff51afe8000 CR3: 000000005a60a005 CR4: 0000000000770ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> rpcprocunregister+0x64/0x70 net/sunrpc/stats.c:310 nfsnetexit+0x1c/0x30 fs/nfs/inode.c:2438 opsexitlist+0x62/0xb0 net/core/netnamespace.c:170 setupnet+0x46c/0x660 net/core/netnamespace.c:372 copynetns+0x244/0x590 net/core/netnamespace.c:505 createnewnamespaces+0x2ed/0x770 kernel/nsproxy.c:110 unsharensproxynamespaces+0xae/0x160 kernel/nsproxy.c:228 ksysunshare+0x342/0x760 kernel/fork.c:3322 dosysunshare kernel/fork.c:3393 [inline] sesysunshare kernel/fork.c:3391 [inline] x64sysunshare+0x1f/0x30 kernel/fork.c:3391 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0x4f/0x110 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x46/0x4e RIP: 0033:0x7f30d0febe5d Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 73 9f 1b 00 f7 d8 64 89 01 48 RSP: 002b:00007f30cfba7cc8 EFLAGS: 00000246 ORIGRAX: 0000000000000110 RAX: ffffffffffffffda RBX: 00000000004bbf80 RCX: 00007f30d0febe5d RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000006c020600 RBP: 00000000004bbf80 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002 R13: 000000000000000b R14: 00007f30d104c530 R15: 0000000000000000 </TASK>