KMSAN: uninit-value in do_xdp_generic

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    93f54a72 instrumented.h: fix KMSAN support
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=16fa5198900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fa4f3b91169c2501
dashboard link: https://syzkaller.appspot.com/bug?extid=007ef8d907f2fb6e17ca
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
userspace arch: i386

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+007ef8d907f2fb6e17ca@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
BUG: KMSAN: uninit-value in netif_receive_generic_xdp net/core/dev.c:4670 [inline]
BUG: KMSAN: uninit-value in do_xdp_generic+0x1312/0x24f0 net/core/dev.c:4735
CPU: 1 PID: 11582 Comm: syz-executor.1 Not tainted 5.8.0-rc5-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+0x1df/0x240 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
 netif_receive_generic_xdp net/core/dev.c:4670 [inline]
 do_xdp_generic+0x1312/0x24f0 net/core/dev.c:4735
 __netif_receive_skb_core+0x9a0/0x5890 net/core/dev.c:5107
 __netif_receive_skb_one_core net/core/dev.c:5279 [inline]
 __netif_receive_skb net/core/dev.c:5395 [inline]
 netif_receive_skb_internal net/core/dev.c:5497 [inline]
 netif_receive_skb+0x56c/0xff0 net/core/dev.c:5556
 tun_rx_batched include/linux/skbuff.h:4327 [inline]
 tun_get_user+0x6df8/0x72f0 drivers/net/tun.c:1972
 tun_chr_write_iter+0x1f2/0x360 drivers/net/tun.c:2001
 call_write_iter include/linux/fs.h:1908 [inline]
 new_sync_write fs/read_write.c:503 [inline]
 vfs_write+0xd98/0x1480 fs/read_write.c:578
 ksys_write+0x267/0x450 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write+0x92/0xb0 fs/read_write.c:640
 __ia32_sys_write+0x4a/0x70 fs/read_write.c:640
 do_syscall_32_irqs_on arch/x86/entry/common.c:430 [inline]
 __do_fast_syscall_32+0x2aa/0x400 arch/x86/entry/common.c:477
 do_fast_syscall_32+0x6b/0xd0 arch/x86/entry/common.c:505
 do_SYSENTER_32+0x73/0x90 arch/x86/entry/common.c:554
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7f1b549
Code: Bad RIP value.
RSP: 002b:00000000f54910cc EFLAGS: 00000296 ORIG_RAX: 0000000000000004
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000020000240
RDX: 000000000000000c RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

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:2839 [inline]
 __kmalloc_node_track_caller+0xb40/0x1200 mm/slub.c:4478
 __kmalloc_reserve net/core/skbuff.c:142 [inline]
 pskb_expand_head+0x20b/0x1b00 net/core/skbuff.c:1627
 netif_receive_generic_xdp net/core/dev.c:4616 [inline]
 do_xdp_generic+0x58c/0x24f0 net/core/dev.c:4735
 __netif_receive_skb_core+0x9a0/0x5890 net/core/dev.c:5107
 __netif_receive_skb_one_core net/core/dev.c:5279 [inline]
 __netif_receive_skb net/core/dev.c:5395 [inline]
 netif_receive_skb_internal net/core/dev.c:5497 [inline]
 netif_receive_skb+0x56c/0xff0 net/core/dev.c:5556
 tun_rx_batched include/linux/skbuff.h:4327 [inline]
 tun_get_user+0x6df8/0x72f0 drivers/net/tun.c:1972
 tun_chr_write_iter+0x1f2/0x360 drivers/net/tun.c:2001
 call_write_iter include/linux/fs.h:1908 [inline]
 new_sync_write fs/read_write.c:503 [inline]
 vfs_write+0xd98/0x1480 fs/read_write.c:578
 ksys_write+0x267/0x450 fs/read_write.c:631
 __do_sys_write fs/read_write.c:643 [inline]
 __se_sys_write+0x92/0xb0 fs/read_write.c:640
 __ia32_sys_write+0x4a/0x70 fs/read_write.c:640
 do_syscall_32_irqs_on arch/x86/entry/common.c:430 [inline]
 __do_fast_syscall_32+0x2aa/0x400 arch/x86/entry/common.c:477
 do_fast_syscall_32+0x6b/0xd0 arch/x86/entry/common.c:505
 do_SYSENTER_32+0x73/0x90 arch/x86/entry/common.c:554
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
=====================================================


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