syzbot ci has tested the following series
[v1] Add IP6IP6 flowtable SW acceleration https://lore.kernel.org/all/20251201-flowtable-offload-ip6ip6-v1-0-1dabf534c... * [PATCH RFC nf-next 1/4] netfilter: Introduce tunnel metadata info in nf_flowtable_ctx struct * [PATCH RFC nf-next 2/4] netfilter: flowtable: Add IP6IP6 rx sw acceleration * [PATCH RFC nf-next 3/4] netfilter: flowtable: Add IP6IP6 tx sw acceleration * [PATCH RFC nf-next 4/4] selftests: netfilter: nft_flowtable.sh: Add IP6IP6 flowtable selftest
and found the following issue: KASAN: slab-use-after-free Read in nf_flow_skb_encap_protocol
Full report is available here: https://ci.syzbot.org/series/df395c22-6768-4a9f-9a96-56b5307acbc6
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KASAN: slab-use-after-free Read in nf_flow_skb_encap_protocol
tree: nf-next URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/netfilter/nf-next.g... base: ff736a286116d462a4067ba258fa351bc0b4ed80 arch: amd64 compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 config: https://ci.syzbot.org/builds/018f7259-7abc-4b77-b40c-e8e520e1e793/config C repro: https://ci.syzbot.org/findings/5cb5bc43-721b-4a9e-a093-4d52aab5ba9f/c_repro syz repro: https://ci.syzbot.org/findings/5cb5bc43-721b-4a9e-a093-4d52aab5ba9f/syz_repr...
================================================================== BUG: KASAN: slab-use-after-free in nf_flow_ip6_tunnel_proto net/netfilter/nf_flow_table_ip.c:383 [inline] BUG: KASAN: slab-use-after-free in nf_flow_skb_encap_protocol+0x1336/0x14e0 net/netfilter/nf_flow_table_ip.c:433 Read of size 2 at addr ffff888115de92b6 by task syz.0.20/5970
CPU: 0 UID: 0 PID: 5970 Comm: syz.0.20 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline] print_report+0xca/0x240 mm/kasan/report.c:482 kasan_report+0x118/0x150 mm/kasan/report.c:595 nf_flow_ip6_tunnel_proto net/netfilter/nf_flow_table_ip.c:383 [inline] nf_flow_skb_encap_protocol+0x1336/0x14e0 net/netfilter/nf_flow_table_ip.c:433 nf_flow_offload_ipv6_lookup net/netfilter/nf_flow_table_ip.c:1065 [inline] nf_flow_offload_ipv6_hook+0x131/0x3380 net/netfilter/nf_flow_table_ip.c:1092 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline] nf_hook_slow+0xc5/0x220 net/netfilter/core.c:623 nf_hook_ingress include/linux/netfilter_netdev.h:34 [inline] nf_ingress net/core/dev.c:5900 [inline] __netif_receive_skb_core+0x241c/0x2f90 net/core/dev.c:5996 __netif_receive_skb_one_core net/core/dev.c:6135 [inline] __netif_receive_skb+0x72/0x380 net/core/dev.c:6250 netif_receive_skb_internal net/core/dev.c:6336 [inline] netif_receive_skb+0x1cb/0x790 net/core/dev.c:6395 tun_rx_batched+0x1b9/0x730 drivers/net/tun.c:1485 tun_get_user+0x2b65/0x3e90 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+0x5c9/0xb30 fs/read_write.c:686 ksys_write+0x145/0x250 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f8b24f8f7c9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f8b25e26038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 00007f8b251e6090 RCX: 00007f8b24f8f7c9 RDX: 000000000000fdef RSI: 0000200000000440 RDI: 0000000000000003 RBP: 00007f8b24ff297f R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007f8b251e6128 R14: 00007f8b251e6090 R15: 00007ffe014b8a38 </TASK>
Allocated by task 5970: kasan_save_stack mm/kasan/common.c:56 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:77 unpoison_slab_object mm/kasan/common.c:342 [inline] __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:368 kasan_slab_alloc include/linux/kasan.h:252 [inline] slab_post_alloc_hook mm/slub.c:4978 [inline] slab_alloc_node mm/slub.c:5288 [inline] kmem_cache_alloc_node_noprof+0x433/0x710 mm/slub.c:5340 __alloc_skb+0x255/0x430 net/core/skbuff.c:679 alloc_skb include/linux/skbuff.h:1383 [inline] alloc_skb_with_frags+0xca/0x890 net/core/skbuff.c:6712 sock_alloc_send_pskb+0x84d/0x980 net/core/sock.c:2995 tun_alloc_skb drivers/net/tun.c:1461 [inline] tun_get_user+0xa43/0x3e90 drivers/net/tun.c:1794 tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1999 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x5c9/0xb30 fs/read_write.c:686 ksys_write+0x145/0x250 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f
Freed by task 5970: kasan_save_stack mm/kasan/common.c:56 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:77 __kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:587 kasan_save_free_info mm/kasan/kasan.h:406 [inline] poison_slab_object mm/kasan/common.c:252 [inline] __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:284 kasan_slab_free include/linux/kasan.h:234 [inline] slab_free_hook mm/slub.c:2543 [inline] slab_free mm/slub.c:6642 [inline] kmem_cache_free+0x19b/0x690 mm/slub.c:6752 icmpv6_param_prob include/linux/icmpv6.h:95 [inline] ipv6_rthdr_rcv+0x150e/0x2020 net/ipv6/exthdrs.c:828 nf_flow_ip6_tunnel_proto net/netfilter/nf_flow_table_ip.c:381 [inline] nf_flow_skb_encap_protocol+0x9b5/0x14e0 net/netfilter/nf_flow_table_ip.c:433 nf_flow_offload_ipv6_lookup net/netfilter/nf_flow_table_ip.c:1065 [inline] nf_flow_offload_ipv6_hook+0x131/0x3380 net/netfilter/nf_flow_table_ip.c:1092 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline] nf_hook_slow+0xc5/0x220 net/netfilter/core.c:623 nf_hook_ingress include/linux/netfilter_netdev.h:34 [inline] nf_ingress net/core/dev.c:5900 [inline] __netif_receive_skb_core+0x241c/0x2f90 net/core/dev.c:5996 __netif_receive_skb_one_core net/core/dev.c:6135 [inline] __netif_receive_skb+0x72/0x380 net/core/dev.c:6250 netif_receive_skb_internal net/core/dev.c:6336 [inline] netif_receive_skb+0x1cb/0x790 net/core/dev.c:6395 tun_rx_batched+0x1b9/0x730 drivers/net/tun.c:1485 tun_get_user+0x2b65/0x3e90 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+0x5c9/0xb30 fs/read_write.c:686 ksys_write+0x145/0x250 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f
The buggy address belongs to the object at ffff888115de9200 which belongs to the cache skbuff_head_cache of size 240 The buggy address is located 182 bytes inside of freed 240-byte region [ffff888115de9200, ffff888115de92f0)
The buggy address belongs to the physical page: page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x115de8 head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 flags: 0x17ff00000000040(head|node=0|zone=2|lastcpupid=0x7ff) page_type: f5(slab) raw: 017ff00000000040 ffff8881036ba8c0 ffffea0004280a80 dead000000000002 raw: 0000000000000000 0000000080150015 00000000f5000000 0000000000000000 head: 017ff00000000040 ffff8881036ba8c0 ffffea0004280a80 dead000000000002 head: 0000000000000000 0000000080150015 00000000f5000000 0000000000000000 head: 017ff00000000001 ffffea0004577a01 00000000ffffffff 00000000ffffffff head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000002 page dumped because: kasan: bad access detected page_owner tracks the page as allocated page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5555, tgid 5555 (dhcpcd), ts 36767395595, free_ts 35122573404 set_page_owner include/linux/page_owner.h:32 [inline] post_alloc_hook+0x234/0x290 mm/page_alloc.c:1845 prep_new_page mm/page_alloc.c:1853 [inline] get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3879 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5178 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416 alloc_slab_page mm/slub.c:3059 [inline] allocate_slab+0x96/0x350 mm/slub.c:3232 new_slab mm/slub.c:3286 [inline] ___slab_alloc+0xf56/0x1990 mm/slub.c:4655 __slab_alloc+0x65/0x100 mm/slub.c:4778 __slab_alloc_node mm/slub.c:4854 [inline] slab_alloc_node mm/slub.c:5276 [inline] kmem_cache_alloc_node_noprof+0x4c5/0x710 mm/slub.c:5340 __alloc_skb+0x255/0x430 net/core/skbuff.c:679 alloc_skb include/linux/skbuff.h:1383 [inline] alloc_skb_with_frags+0xca/0x890 net/core/skbuff.c:6712 sock_alloc_send_pskb+0x84d/0x980 net/core/sock.c:2995 unix_dgram_sendmsg+0x454/0x1840 net/unix/af_unix.c:2139 sock_sendmsg_nosec net/socket.c:727 [inline] __sock_sendmsg+0x21c/0x270 net/socket.c:742 sock_write_iter+0x279/0x360 net/socket.c:1195 do_iter_readv_writev+0x623/0x8c0 fs/read_write.c:-1 vfs_writev+0x31a/0x960 fs/read_write.c:1057 page last free pid 5262 tgid 5262 stack trace: reset_page_owner include/linux/page_owner.h:25 [inline] free_pages_prepare mm/page_alloc.c:1394 [inline] __free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2901 __slab_free+0x2e7/0x390 mm/slub.c:5970 qlink_free mm/kasan/quarantine.c:163 [inline] qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:352 kasan_slab_alloc include/linux/kasan.h:252 [inline] slab_post_alloc_hook mm/slub.c:4978 [inline] slab_alloc_node mm/slub.c:5288 [inline] kmem_cache_alloc_noprof+0x367/0x6e0 mm/slub.c:5295 getname_flags+0xb8/0x540 fs/namei.c:146 getname include/linux/fs.h:2924 [inline] do_sys_openat2+0xbc/0x1c0 fs/open.c:1431 do_sys_open fs/open.c:1452 [inline] __do_sys_openat fs/open.c:1468 [inline] __se_sys_openat fs/open.c:1463 [inline] __x64_sys_openat+0x138/0x170 fs/open.c:1463 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f
Memory state around the buggy address: ffff888115de9180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff888115de9200: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888115de9280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc
^ ffff888115de9300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff888115de9380: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ==================================================================
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If these findings have caused you to resend the series or submit a separate fix, please add the following tag to your commit message: Tested-by: syzbot@syzkaller.appspotmail.com
--- This report is generated by a bot. It may contain errors. syzbot ci engineers can be reached at syzkaller@googlegroups.com.