KMSAN: uninit-value in __nla_validate_parse

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    f0d5ec90 kmsan: apply __no_sanitize_memory to dotraplinkag..
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=1314b629100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=86e4f8af239686c6
dashboard link: https://syzkaller.appspot.com/bug?extid=6c73a580c3aec0f65123
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6c73a580c3aec0f65123@xxxxxxxxxxxxxxxxxxxxxxxxx

netlink: 4 bytes leftover after parsing attributes in process `syz-executor.2'.
=====================================================
BUG: KMSAN: uninit-value in nla_ok include/net/netlink.h:1094 [inline]
BUG: KMSAN: uninit-value in __nla_validate_parse+0x422/0x3450 lib/nlattr.c:369
CPU: 1 PID: 28976 Comm: syz-executor.2 Not tainted 5.7.0-rc4-syzkaller #0
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+0x1c9/0x220 lib/dump_stack.c:118
 kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
 __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
 nla_ok include/net/netlink.h:1094 [inline]
 __nla_validate_parse+0x422/0x3450 lib/nlattr.c:369
 __nla_parse+0x137/0x150 lib/nlattr.c:478
 nla_parse_nested include/net/netlink.h:1147 [inline]
 fl_set_erspan_opt+0x30e/0xd40 net/sched/cls_flower.c:1040
 fl_set_enc_opt net/sched/cls_flower.c:1198 [inline]
 fl_set_key+0x6322/0x8e10 net/sched/cls_flower.c:1471
 fl_set_parms net/sched/cls_flower.c:1707 [inline]
 fl_change+0x1202/0x7530 net/sched/cls_flower.c:1806
 tc_new_tfilter+0x31a8/0x4f40 net/sched/cls_api.c:2168
 rtnetlink_rcv_msg+0xcb7/0x1570 net/core/rtnetlink.c:5445
 netlink_rcv_skb+0x451/0x650 net/netlink/af_netlink.c:2469
 rtnetlink_rcv+0x50/0x60 net/core/rtnetlink.c:5472
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0xf9e/0x1100 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0x1246/0x14d0 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x12b6/0x1350 net/socket.c:2362
 ___sys_sendmsg net/socket.c:2416 [inline]
 __sys_sendmmsg+0x5fe/0xd60 net/socket.c:2506
 __do_sys_sendmmsg net/socket.c:2535 [inline]
 __se_sys_sendmmsg+0xbd/0xe0 net/socket.c:2532
 __x64_sys_sendmmsg+0x56/0x70 net/socket.c:2532
 do_syscall_64+0xb8/0x160 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45ca59
Code: 0d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f1dee04dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00000000004fd380 RCX: 000000000045ca59
RDX: 010efe10675dec16 RSI: 0000000020000200 RDI: 0000000000000003
RBP: 000000000078bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000900 R14: 00000000004cbcfa R15: 00007f1dee04e6d4

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
 kmsan_internal_poison_shadow+0x66/0xd0 mm/kmsan/kmsan.c:127
 kmsan_slab_alloc+0x8a/0xe0 mm/kmsan/kmsan_hooks.c:80
 slab_alloc_node mm/slub.c:2802 [inline]
 __kmalloc_node_track_caller+0xb40/0x1200 mm/slub.c:4436
 __kmalloc_reserve net/core/skbuff.c:142 [inline]
 __alloc_skb+0x2fd/0xac0 net/core/skbuff.c:210
 alloc_skb include/linux/skbuff.h:1083 [inline]
 netlink_alloc_large_skb net/netlink/af_netlink.c:1175 [inline]
 netlink_sendmsg+0x7d3/0x14d0 net/netlink/af_netlink.c:1893
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x12b6/0x1350 net/socket.c:2362
 ___sys_sendmsg net/socket.c:2416 [inline]
 __sys_sendmmsg+0x5fe/0xd60 net/socket.c:2506
 __do_sys_sendmmsg net/socket.c:2535 [inline]
 __se_sys_sendmmsg+0xbd/0xe0 net/socket.c:2532
 __x64_sys_sendmmsg+0x56/0x70 net/socket.c:2532
 do_syscall_64+0xb8/0x160 arch/x86/entry/common.c:297
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
=====================================================


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