[syzbot] [net?] KMSAN: uninit-value in erspan_build_header (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a4145ce1e7bc Merge tag 'bcachefs-2024-03-19' of https://ev..
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=154a06a5180000
kernel config: https://syzkaller.appspot.com/x/.config?x=5c1d7ee7e74661a8
dashboard link: https://syzkaller.appspot.com/bug?extid=9e27778c0edc62cb97d8
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1126e1a5180000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15c14e31180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ce90c7e9c4b9/disk-a4145ce1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/fc2e82754c55/vmlinux-a4145ce1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dfc8b656ea07/bzImage-a4145ce1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9e2777...@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in erspan_build_header+0x170/0x2f0 include/net/erspan.h:197
erspan_build_header+0x170/0x2f0 include/net/erspan.h:197
erspan_xmit+0x128a/0x1ec0 net/ipv4/ip_gre.c:706
__netdev_start_xmit include/linux/netdevice.h:4903 [inline]
netdev_start_xmit include/linux/netdevice.h:4917 [inline]
xmit_one net/core/dev.c:3531 [inline]
dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3547
sch_direct_xmit+0x3c5/0xd50 net/sched/sch_generic.c:343
__dev_xmit_skb net/core/dev.c:3760 [inline]
__dev_queue_xmit+0x2e6a/0x52c0 net/core/dev.c:4301
dev_queue_xmit include/linux/netdevice.h:3091 [inline]
__bpf_tx_skb net/core/filter.c:2136 [inline]
__bpf_redirect_common net/core/filter.c:2180 [inline]
__bpf_redirect+0x14a6/0x1620 net/core/filter.c:2187
____bpf_clone_redirect net/core/filter.c:2460 [inline]
bpf_clone_redirect+0x328/0x470 net/core/filter.c:2432
___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:1997
__bpf_prog_run512+0xb5/0xe0 kernel/bpf/core.c:2238
bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
__bpf_prog_run include/linux/filter.h:657 [inline]
bpf_prog_run include/linux/filter.h:664 [inline]
bpf_test_run+0x499/0xc30 net/bpf/test_run.c:425
bpf_prog_test_run_skb+0x14ea/0x1f20 net/bpf/test_run.c:1058
bpf_prog_test_run+0x6b7/0xad0 kernel/bpf/syscall.c:4240
__sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5649
__do_sys_bpf kernel/bpf/syscall.c:5738 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5736 [inline]
__x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5736
do_syscall_64+0xd5/0x1f0
entry_SYSCALL_64_after_hwframe+0x6d/0x75

Uninit was created at:
slab_post_alloc_hook mm/slub.c:3804 [inline]
slab_alloc_node mm/slub.c:3845 [inline]
kmem_cache_alloc_node+0x613/0xc50 mm/slub.c:3888
kmalloc_reserve+0x13d/0x4a0 net/core/skbuff.c:577
pskb_expand_head+0x222/0x19d0 net/core/skbuff.c:2245
__skb_cow include/linux/skbuff.h:3671 [inline]
skb_cow_head include/linux/skbuff.h:3705 [inline]
erspan_xmit+0xb08/0x1ec0 net/ipv4/ip_gre.c:692
__netdev_start_xmit include/linux/netdevice.h:4903 [inline]
netdev_start_xmit include/linux/netdevice.h:4917 [inline]
xmit_one net/core/dev.c:3531 [inline]
dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3547
sch_direct_xmit+0x3c5/0xd50 net/sched/sch_generic.c:343
__dev_xmit_skb net/core/dev.c:3760 [inline]
__dev_queue_xmit+0x2e6a/0x52c0 net/core/dev.c:4301
dev_queue_xmit include/linux/netdevice.h:3091 [inline]
__bpf_tx_skb net/core/filter.c:2136 [inline]
__bpf_redirect_common net/core/filter.c:2180 [inline]
__bpf_redirect+0x14a6/0x1620 net/core/filter.c:2187
____bpf_clone_redirect net/core/filter.c:2460 [inline]
bpf_clone_redirect+0x328/0x470 net/core/filter.c:2432
___bpf_prog_run+0x13fe/0xe0f0 kernel/bpf/core.c:1997
__bpf_prog_run512+0xb5/0xe0 kernel/bpf/core.c:2238
bpf_dispatcher_nop_func include/linux/bpf.h:1234 [inline]
__bpf_prog_run include/linux/filter.h:657 [inline]
bpf_prog_run include/linux/filter.h:664 [inline]
bpf_test_run+0x499/0xc30 net/bpf/test_run.c:425
bpf_prog_test_run_skb+0x14ea/0x1f20 net/bpf/test_run.c:1058
bpf_prog_test_run+0x6b7/0xad0 kernel/bpf/syscall.c:4240
__sys_bpf+0x6aa/0xd90 kernel/bpf/syscall.c:5649
__do_sys_bpf kernel/bpf/syscall.c:5738 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5736 [inline]
__x64_sys_bpf+0xa0/0xe0 kernel/bpf/syscall.c:5736
do_syscall_64+0xd5/0x1f0
entry_SYSCALL_64_after_hwframe+0x6d/0x75

CPU: 0 PID: 5041 Comm: syz-executor167 Not tainted 6.8.0-syzkaller-11743-ga4145ce1e7bc #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/29/2024
=====================================================


---
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[Eric Dumazet]

Patch sent for review :
https://patchwork.kernel.org/project/netdevbpf/patch/20240322122407.1...@google.com/