KMSAN: uninit-value in ip6_compressed_string

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: fffec98ae2a6 net: proper support for CONFIG_GENERIC_CSUM o..
git tree: https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=156ad1f5400000
kernel config: https://syzkaller.appspot.com/x/.config?x=56b48b46dafe4516
dashboard link: https://syzkaller.appspot.com/bug?extid=047a11c361b872896a4f
compiler: clang version 8.0.0 (trunk 343298)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1031326d400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16212b0b400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+047a11...@syzkaller.appspotmail.com

==================================================================
BUG: KMSAN: uninit-value in ip6_compressed_string+0x1a9/0x1460
lib/vsprintf.c:1161
CPU: 1 PID: 6762 Comm: syz-executor445 Not tainted 4.20.0-rc3+ #95
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x32d/0x480 lib/dump_stack.c:113
kmsan_report+0x12c/0x290 mm/kmsan/kmsan.c:683
__msan_warning+0x76/0xc0 mm/kmsan/kmsan_instr.c:330
ip6_compressed_string+0x1a9/0x1460 lib/vsprintf.c:1161
ip6_addr_string+0x165/0x2b0 lib/vsprintf.c:1247
pointer+0x110e/0x1520 lib/vsprintf.c:1911
vsnprintf+0xabf/0x3110 lib/vsprintf.c:2300
snprintf+0x246/0x290 lib/vsprintf.c:2429
rpc_ntop6_noscopeid net/sunrpc/addr.c:56 [inline]
rpc_sockaddr2uaddr+0x3aa/0x6f0 net/sunrpc/addr.c:281
rpcb_getport_async+0x10d4/0x1770 net/sunrpc/rpcb_clnt.c:773
call_bind+0x1a8/0x260 net/sunrpc/clnt.c:1802
__rpc_execute+0xacb/0x19c0 net/sunrpc/sched.c:832
rpc_execute+0x6ad/0x940 net/sunrpc/sched.c:900
rpc_run_task+0xc42/0xe70 net/sunrpc/clnt.c:1065
rpc_call_sync net/sunrpc/clnt.c:1094 [inline]
rpc_ping net/sunrpc/clnt.c:2516 [inline]
rpc_create_xprt+0x6a9/0xe80 net/sunrpc/clnt.c:480
rpc_create+0xa78/0xb30 net/sunrpc/clnt.c:588
nfs_create_rpc_client+0x752/0x860 fs/nfs/client.c:523
nfs_init_client+0xb8/0x1d0 fs/nfs/client.c:634
nfs_get_client+0x14fc/0x1720 fs/nfs/client.c:425
nfs_init_server fs/nfs/client.c:670 [inline]
nfs_create_server+0xbd7/0x3290 fs/nfs/client.c:954
nfs_try_mount+0x4de/0x14b0 fs/nfs/super.c:1884
nfs_fs_mount+0x393d/0x4000 fs/nfs/super.c:2695
mount_fs+0x282/0x790 fs/super.c:1261
vfs_kern_mount+0x231/0x8c0 fs/namespace.c:961
do_new_mount fs/namespace.c:2469 [inline]
do_mount+0xd1f/0x5ac0 fs/namespace.c:2801
ksys_mount+0x32e/0x3d0 fs/namespace.c:3017
__do_sys_mount fs/namespace.c:3031 [inline]
__se_sys_mount+0xe5/0x110 fs/namespace.c:3028
__x64_sys_mount+0x62/0x80 fs/namespace.c:3028
do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x4401c9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff7eefaf48 EFLAGS: 00000286 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 00000000004401c9
RDX: 0000000020000180 RSI: 0000000020000140 RDI: 0000000000000000
RBP: 00000000006ca018 R08: 000000002000a000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 0000000000401a50
R13: 0000000000401ae0 R14: 0000000000000000 R15: 0000000000000000

Uninit was stored to memory at:
kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
kmsan_save_stack mm/kmsan/kmsan.c:261 [inline]
kmsan_internal_chain_origin+0x13d/0x240 mm/kmsan/kmsan.c:469
kmsan_memcpy_memmove_metadata+0x1a9/0xf70 mm/kmsan/kmsan.c:344
kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:362
__msan_memcpy+0x61/0x70 mm/kmsan/kmsan_instr.c:162
ip6_compressed_string+0x89/0x1460 lib/vsprintf.c:1154
ip6_addr_string+0x165/0x2b0 lib/vsprintf.c:1247
pointer+0x110e/0x1520 lib/vsprintf.c:1911
vsnprintf+0xabf/0x3110 lib/vsprintf.c:2300
snprintf+0x246/0x290 lib/vsprintf.c:2429
rpc_ntop6_noscopeid net/sunrpc/addr.c:56 [inline]
rpc_sockaddr2uaddr+0x3aa/0x6f0 net/sunrpc/addr.c:281
rpcb_getport_async+0x10d4/0x1770 net/sunrpc/rpcb_clnt.c:773
call_bind+0x1a8/0x260 net/sunrpc/clnt.c:1802
__rpc_execute+0xacb/0x19c0 net/sunrpc/sched.c:832
rpc_execute+0x6ad/0x940 net/sunrpc/sched.c:900
rpc_run_task+0xc42/0xe70 net/sunrpc/clnt.c:1065
rpc_call_sync net/sunrpc/clnt.c:1094 [inline]
rpc_ping net/sunrpc/clnt.c:2516 [inline]
rpc_create_xprt+0x6a9/0xe80 net/sunrpc/clnt.c:480
rpc_create+0xa78/0xb30 net/sunrpc/clnt.c:588
nfs_create_rpc_client+0x752/0x860 fs/nfs/client.c:523
nfs_init_client+0xb8/0x1d0 fs/nfs/client.c:634
nfs_get_client+0x14fc/0x1720 fs/nfs/client.c:425
nfs_init_server fs/nfs/client.c:670 [inline]
nfs_create_server+0xbd7/0x3290 fs/nfs/client.c:954
nfs_try_mount+0x4de/0x14b0 fs/nfs/super.c:1884
nfs_fs_mount+0x393d/0x4000 fs/nfs/super.c:2695
mount_fs+0x282/0x790 fs/super.c:1261
vfs_kern_mount+0x231/0x8c0 fs/namespace.c:961
do_new_mount fs/namespace.c:2469 [inline]
do_mount+0xd1f/0x5ac0 fs/namespace.c:2801
ksys_mount+0x32e/0x3d0 fs/namespace.c:3017
__do_sys_mount fs/namespace.c:3031 [inline]
__se_sys_mount+0xe5/0x110 fs/namespace.c:3028
__x64_sys_mount+0x62/0x80 fs/namespace.c:3028
do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291
entry_SYSCALL_64_after_hwframe+0x63/0xe7

Local variable description: ----addr@rpcb_getport_async
Variable was created at:
rpcb_getport_async+0xb3/0x1770 net/sunrpc/rpcb_clnt.c:673
call_bind+0x1a8/0x260 net/sunrpc/clnt.c:1802
==================================================================


---
This bug is generated by a bot. It may contain errors.
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[Tetsuo Handa]

syzbot is reporting uninitialized value at rpc_sockaddr2uaddr() [1]. This
is because syzbot is setting AF_INET6 to "struct sockaddr_in"->sin_family
(which is embedded into user-visible "struct nfs_mount_data" structure)
despite nfs23_validate_mount_data() cannot pass sizeof(struct sockaddr_in6)
bytes of AF_INET6 address to rpc_sockaddr2uaddr().

Since "struct nfs_mount_data" structure is user-visible, we can't change
"struct nfs_mount_data" to use "struct sockaddr_storage". Therefore,
assuming that everybody is using AF_INET family when passing address via
"struct nfs_mount_data"->addr, reject if its sin_family is not AF_INET.

[1] https://syzkaller.appspot.com/bug?id=599993614e7cbbf66bc2656a919ab2a95fb5d75c

Reported-by: syzbot <syzbot+047a11...@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin...@I-love.SAKURA.ne.jp>
---
fs/nfs/super.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 23790c7..c27ac96 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -2041,7 +2041,8 @@ static int nfs23_validate_mount_data(void *options,
memcpy(sap, &data->addr, sizeof(data->addr));
args->nfs_server.addrlen = sizeof(data->addr);
args->nfs_server.port = ntohs(data->addr.sin_port);
- if (!nfs_verify_server_address(sap))
+ if (sap->sa_family != AF_INET ||
+ !nfs_verify_server_address(sap))
goto out_no_address;

if (!(data->flags & NFS_MOUNT_TCP))
--
1.8.3.1