KMSAN: uninit-value in bpf_skb_load_helper_32

[syzbot]

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@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
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
=====================================================


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