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SubjectKMSAN: uninit-value in bpf_skb_load_helper_32
From
Hello,

syzbot found the following crash on:

HEAD commit: 9535d09e page_alloc: drop a call to kmsan_split_page()
git tree: https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=105fa39be00000
kernel config: https://syzkaller.appspot.com/x/.config?x=a5915107b3106aaa
dashboard link: https://syzkaller.appspot.com/bug?extid=ae94def68efda6a4be52
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17314f58100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+ae94def68efda6a4be52@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in __arch_swab32 arch/x86/include/uapi/asm/swab.h:10 [inline]
BUG: KMSAN: uninit-value in __fswab32 include/uapi/linux/swab.h:60 [inline]
BUG: KMSAN: uninit-value in __swab32p include/uapi/linux/swab.h:189 [inline]
BUG: KMSAN: uninit-value in __be32_to_cpup include/uapi/linux/byteorder/little_endian.h:82 [inline]
BUG: KMSAN: uninit-value in get_unaligned_be32 include/linux/unaligned/access_ok.h:30 [inline]
BUG: KMSAN: uninit-value in ____bpf_skb_load_helper_32 net/core/filter.c:246 [inline]
BUG: KMSAN: uninit-value in bpf_skb_load_helper_32+0x18b/0x2d0 net/core/filter.c:232
CPU: 0 PID: 10091 Comm: syz-executor.0 Not tainted 5.6.0-rc7-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:118
__msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
__arch_swab32 arch/x86/include/uapi/asm/swab.h:10 [inline]
__fswab32 include/uapi/linux/swab.h:60 [inline]
__swab32p include/uapi/linux/swab.h:189 [inline]
__be32_to_cpup include/uapi/linux/byteorder/little_endian.h:82 [inline]
get_unaligned_be32 include/linux/unaligned/access_ok.h:30 [inline]
____bpf_skb_load_helper_32 net/core/filter.c:246 [inline]
bpf_skb_load_helper_32+0x18b/0x2d0 net/core/filter.c:232

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:82
slab_alloc_node mm/slub.c:2801 [inline]
__kmalloc_node_track_caller+0xb40/0x1200 mm/slub.c:4420
__kmalloc_reserve net/core/skbuff.c:142 [inline]
__alloc_skb+0x2fd/0xac0 net/core/skbuff.c:210
alloc_skb include/linux/skbuff.h:1081 [inline]
netlink_dump+0x26b/0x1ab0 net/netlink/af_netlink.c:2219
netlink_recvmsg+0xe88/0x1910 net/netlink/af_netlink.c:2001
____sys_recvmsg+0x1173/0x1240 net/socket.c:886
___sys_recvmsg net/socket.c:2610 [inline]
do_recvmmsg+0x6f3/0x1eb0 net/socket.c:2708
__sys_recvmmsg net/socket.c:2789 [inline]
__do_sys_recvmmsg net/socket.c:2810 [inline]
__se_sys_recvmmsg+0x25d/0x350 net/socket.c:2803
__x64_sys_recvmmsg+0x62/0x80 net/socket.c:2803
do_syscall_64+0xb8/0x160 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x44/0xa9
=====================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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