[syzbot] [bpf?] [net?] KASAN: stack-out-of-bounds Write in dev_map_redirect_multi

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 24cf78c73831 net/mlx5e: SHAMPO, Switch to header memcpy
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1092c65a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2c36acc86fd56a9d
dashboard link: https://syzkaller.appspot.com/bug?extid=10cc7f13760b31bd2e61
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9514a76ff576/disk-24cf78c7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5f26244320f5/vmlinux-24cf78c7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e0823b49ca48/bzImage-24cf78c7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+10cc7f...@syzkaller.appspotmail.com

netlink: 'syz.1.9102': attribute type 1 has an invalid length.
==================================================================
BUG: KASAN: stack-out-of-bounds in get_upper_ifindexes kernel/bpf/devmap.c:601 [inline]
BUG: KASAN: stack-out-of-bounds in dev_map_redirect_multi+0x1bb/0xa00 kernel/bpf/devmap.c:736
Write of size 4 at addr ffffc9000b117164 by task syz.1.9102/9450

CPU: 1 UID: 0 PID: 9450 Comm: syz.1.9102 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xba/0x230 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
get_upper_ifindexes kernel/bpf/devmap.c:601 [inline]
dev_map_redirect_multi+0x1bb/0xa00 kernel/bpf/devmap.c:736
xdp_do_generic_redirect_map net/core/filter.c:4556 [inline]
xdp_do_generic_redirect+0x669/0x820 net/core/filter.c:4619
do_xdp_generic+0xcf7/0x12e0 net/core/dev.c:5612
__netif_receive_skb_core+0x10e5/0x3150 net/core/dev.c:5961
__netif_receive_skb_one_core net/core/dev.c:6149 [inline]
__netif_receive_skb net/core/dev.c:6264 [inline]
netif_receive_skb_internal net/core/dev.c:6350 [inline]
netif_receive_skb+0x1fe/0xbb0 net/core/dev.c:6409
tun_rx_batched+0x1de/0x790 drivers/net/tun.c:1485
tun_get_user+0x2a78/0x3dd0 drivers/net/tun.c:1953
tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1999
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x61d/0xb90 fs/read_write.c:686
ksys_write+0x150/0x270 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f937215b78e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007f9372ffafb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f9372ffb6c0 RCX: 00007f937215b78e
RDX: 0000000000000086 RSI: 0000200000000780 RDI: 00000000000000c8
RBP: 00007f9372208c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9372416038 R14: 00007f9372415fa0 R15: 00007fffe06ef058
</TASK>

The buggy address belongs to stack of task syz.1.9102/9450
and is located at offset 100 in frame:
dev_map_redirect_multi+0x0/0xa00 include/linux/skbuff.h:2833

This frame has 2 objects:
[32, 40) 'iter.i'
[64, 100) 'excluded_devices'

The buggy address belongs to a 8-page vmalloc region starting at 0xffffc9000b110000 allocated at copy_process+0x508/0x3980 kernel/fork.c:2052
The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x94807
memcg:ffff88814237e782
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 0000000000000000 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff ffff88814237e782
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x29c2(GFP_NOWAIT|__GFP_HIGHMEM|__GFP_IO|__GFP_FS|__GFP_ZERO), pid 2, tgid 2 (kthreadd), ts 1433078116205, free_ts 1432956594052
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x228/0x280 mm/page_alloc.c:1884
prep_new_page mm/page_alloc.c:1892 [inline]
get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3945
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5240
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2486
alloc_frozen_pages_noprof mm/mempolicy.c:2557 [inline]
alloc_pages_noprof+0xa8/0x190 mm/mempolicy.c:2577
vm_area_alloc_pages mm/vmalloc.c:3649 [inline]
__vmalloc_area_node mm/vmalloc.c:3863 [inline]
__vmalloc_node_range_noprof+0x79b/0x1730 mm/vmalloc.c:4051
__vmalloc_node_noprof+0xc2/0x100 mm/vmalloc.c:4111
alloc_thread_stack_node kernel/fork.c:354 [inline]
dup_task_struct+0x228/0x9a0 kernel/fork.c:923
copy_process+0x508/0x3980 kernel/fork.c:2052
kernel_clone+0x248/0x870 kernel/fork.c:2651
kernel_thread+0x13f/0x1b0 kernel/fork.c:2712
create_kthread kernel/kthread.c:486 [inline]
kthreadd+0x4f9/0x6f0 kernel/kthread.c:844
ret_from_fork+0x51b/0xa40 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
page last free pid 8089 tgid 8089 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1433 [inline]
__free_frozen_pages+0xbf8/0xd70 mm/page_alloc.c:2973
__folio_put+0x414/0x4f0 mm/swap.c:112
put_netmem include/net/netmem.h:420 [inline]
skb_page_unref include/linux/skbuff_ref.h:43 [inline]
__skb_frag_unref include/linux/skbuff_ref.h:56 [inline]
skb_release_data+0x4cb/0x940 net/core/skbuff.c:1122
skb_release_all net/core/skbuff.c:1203 [inline]
__kfree_skb+0x5d/0x210 net/core/skbuff.c:1217
kfree_skb_reason include/linux/skbuff.h:1322 [inline]
__skb_queue_purge_reason include/linux/skbuff.h:3426 [inline]
__skb_queue_purge include/linux/skbuff.h:3431 [inline]
virtio_transport_remove_sock net/vmw_vsock/virtio_transport_common.c:1224 [inline]
virtio_transport_cancel_close_work net/vmw_vsock/virtio_transport_common.c:1237 [inline]
virtio_transport_do_close+0x251/0x3c0 net/vmw_vsock/virtio_transport_common.c:1255
virtio_transport_recv_connected+0x3c4/0xf10 net/vmw_vsock/virtio_transport_common.c:1464
virtio_transport_recv_pkt+0x17a4/0x2b70 net/vmw_vsock/virtio_transport_common.c:1693
vsock_loopback_work+0x32c/0x3f0 net/vmw_vsock/vsock_loopback.c:142
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0xaec/0x17a0 kernel/workqueue.c:3340
worker_thread+0xda6/0x1360 kernel/workqueue.c:3421
kthread+0x726/0x8b0 kernel/kthread.c:463
ret_from_fork+0x51b/0xa40 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

Memory state around the buggy address:
ffffc9000b117000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffc9000b117080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffffc9000b117100: f1 f1 f1 f1 00 f2 f2 f2 00 00 00 00 04 f3 f3 f3
^
ffffc9000b117180: f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
ffffc9000b117200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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