KASAN: slab-use-after-free Read in sit_tunnel_xmit

Status: fixed on 2026/07/15 08:27
Subsystems: net
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+6eb9ca986d80f6f88cf9@syzkaller.appspotmail.com
Fix commit: f0e42f0c4337 ipv6: sit: reload inner IPv6 header after GSO offloads
First crash: 49d, last: 49d
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
8c497eb1 assessment-security DenialOfService: ❌ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-use-after-free Read in sit_tunnel_xmit 2026/06/11 00:08 2026/06/11 00:08 2026/06/11 00:12 416ea548 

			
				
	

	
	

		f1ecce84
		assessment-security
		
			
		
		💥
		KASAN: slab-use-after-free Read in sit_tunnel_xmit
		2026/06/09 13:30
		2026/06/09 13:30
		2026/06/09 13:30
		c36c07f6
		
			
failed to run ["git" "-c" "core.hooksPath=/dev/null" "fetch" "--force" "--tags" "5c96e23a32a280262291fe5d31d8f7dc6f666b47" "c93952cc0034dc491cf082d1df11e996513a53ed"]: exit status 128
error: insuffici...

			
				
truncated to first 200 bytes; open job for full error

			
				
	

	
	



			

		

	

	
	

		

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			Discussions (2)
		

		

			
			
			



	
	

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			Re: [PATCH] ipv6: sit: reload inner IPv6 header after GSO offloads
			1 (1)
			2026/06/07 06:35
		

	
		

			[syzbot] [net?] KASAN: slab-use-after-free Read in sit_tunnel_xmit
			0 (1)
			2026/06/07 06:33
		

	
	




			
			
		

	

	

	
	
Sample crash report:

	
==================================================================
BUG: KASAN: slab-use-after-free in ipv6_get_dsfield include/net/dsfield.h:24 [inline]
BUG: KASAN: slab-use-after-free in ipip6_tunnel_xmit net/ipv6/sit.c:1021 [inline]
BUG: KASAN: slab-use-after-free in sit_tunnel_xmit+0x19b5/0x1b80 net/ipv6/sit.c:1072
Read of size 2 at addr ffff88801bba9760 by task syz.0.1430/10890

CPU: 0 UID: 0 PID: 10890 Comm: syz.0.1430 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 ipv6_get_dsfield include/net/dsfield.h:24 [inline]
 ipip6_tunnel_xmit net/ipv6/sit.c:1021 [inline]
 sit_tunnel_xmit+0x19b5/0x1b80 net/ipv6/sit.c:1072
 __netdev_start_xmit include/linux/netdevice.h:5368 [inline]
 netdev_start_xmit include/linux/netdevice.h:5377 [inline]
 xmit_one net/core/dev.c:3888 [inline]
 dev_hard_start_xmit+0x2cd/0x830 net/core/dev.c:3904
 __dev_queue_xmit+0x14d9/0x3950 net/core/dev.c:4870
 packet_snd net/packet/af_packet.c:3082 [inline]
 packet_sendmsg+0x3c81/0x4fb0 net/packet/af_packet.c:3114
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 __sys_sendto+0x672/0x710 net/socket.c:2265
 __do_sys_sendto net/socket.c:2272 [inline]
 __se_sys_sendto net/socket.c:2268 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2268
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff06c39ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff06d1e8028 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 00007ff06c615fa0 RCX: 00007ff06c39ce59
RDX: 000000000000fc13 RSI: 0000200000000280 RDI: 0000000000000005
RBP: 00007ff06c432d6f R08: 0000000000000000 R09: 000000000000002f
R10: 0000000000000800 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff06c616038 R14: 00007ff06c615fa0 R15: 00007ffe13a440e8
 </TASK>

Allocated by task 10890:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 unpoison_slab_object mm/kasan/common.c:340 [inline]
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4570 [inline]
 slab_alloc_node mm/slub.c:4899 [inline]
 kmem_cache_alloc_node_noprof+0x384/0x690 mm/slub.c:4951
 kmalloc_reserve net/core/skbuff.c:613 [inline]
 __alloc_skb+0x27d/0x7d0 net/core/skbuff.c:713
 alloc_skb include/linux/skbuff.h:1385 [inline]
 alloc_skb_with_frags+0xc8/0x760 net/core/skbuff.c:6766
 sock_alloc_send_pskb+0x878/0x990 net/core/sock.c:3002
 packet_alloc_skb net/packet/af_packet.c:2932 [inline]
 packet_snd net/packet/af_packet.c:3025 [inline]
 packet_sendmsg+0x315a/0x4fb0 net/packet/af_packet.c:3114
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 __sys_sendto+0x672/0x710 net/socket.c:2265
 __do_sys_sendto net/socket.c:2272 [inline]
 __se_sys_sendto net/socket.c:2268 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2268
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 10890:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2689 [inline]
 slab_free mm/slub.c:6251 [inline]
 kfree+0x1c5/0x640 mm/slub.c:6566
 skb_kfree_head net/core/skbuff.c:1075 [inline]
 skb_free_head net/core/skbuff.c:1087 [inline]
 pskb_expand_head+0x458/0x1390 net/core/skbuff.c:2335
 skb_header_unclone include/linux/skbuff.h:2087 [inline]
 iptunnel_handle_offloads+0x362/0x630 net/ipv4/ip_tunnel_core.c:185
 ipip6_tunnel_xmit net/ipv6/sit.c:960 [inline]
 sit_tunnel_xmit+0x92a/0x1b80 net/ipv6/sit.c:1072
 __netdev_start_xmit include/linux/netdevice.h:5368 [inline]
 netdev_start_xmit include/linux/netdevice.h:5377 [inline]
 xmit_one net/core/dev.c:3888 [inline]
 dev_hard_start_xmit+0x2cd/0x830 net/core/dev.c:3904
 __dev_queue_xmit+0x14d9/0x3950 net/core/dev.c:4870
 packet_snd net/packet/af_packet.c:3082 [inline]
 packet_sendmsg+0x3c81/0x4fb0 net/packet/af_packet.c:3114
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 __sys_sendto+0x672/0x710 net/socket.c:2265
 __do_sys_sendto net/socket.c:2272 [inline]
 __se_sys_sendto net/socket.c:2268 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2268
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88801bba96c0
 which belongs to the cache skbuff_small_head of size 704
The buggy address is located 160 bytes inside of
 freed 704-byte region [ffff88801bba96c0, ffff88801bba9980)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1bba8
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801f2ad8c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800130013 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801f2ad8c0 dead000000000100 dead000000000122
head: 0000000000000000 0000000800130013 00000000f5000000 0000000000000000
head: 00fff00000000002 ffffffffffffff01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000004
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5003, tgid 5003 (udevd), ts 31613474311, free_ts 31513004909
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x22d/0x280 mm/page_alloc.c:1853
 prep_new_page mm/page_alloc.c:1861 [inline]
 get_page_from_freelist+0x2593/0x2610 mm/page_alloc.c:3941
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5221
 alloc_slab_page mm/slub.c:3278 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3467
 new_slab mm/slub.c:3525 [inline]
 refill_objects+0x339/0x3d0 mm/slub.c:7272
 refill_sheaf mm/slub.c:2816 [inline]
 __pcs_replace_empty_main+0x321/0x720 mm/slub.c:4652
 alloc_from_pcs mm/slub.c:4750 [inline]
 slab_alloc_node mm/slub.c:4884 [inline]
 kmem_cache_alloc_node_noprof+0x441/0x690 mm/slub.c:4951
 kmalloc_reserve net/core/skbuff.c:613 [inline]
 __alloc_skb+0x27d/0x7d0 net/core/skbuff.c:713
 netlink_sendmsg+0x5d4/0xb40 net/netlink/af_netlink.c:1874
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 ____sys_sendmsg+0x972/0x9f0 net/socket.c:2698
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2752
 __sys_sendmsg net/socket.c:2784 [inline]
 __do_sys_sendmsg net/socket.c:2789 [inline]
 __se_sys_sendmsg net/socket.c:2787 [inline]
 __x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2787
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5001 tgid 5001 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1397 [inline]
 __free_frozen_pages+0xc1c/0xd30 mm/page_alloc.c:2938
 __slab_free+0x274/0x2c0 mm/slub.c:5613
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x99/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4570 [inline]
 slab_alloc_node mm/slub.c:4899 [inline]
 kmem_cache_alloc_noprof+0x2bc/0x650 mm/slub.c:4906
 lsm_file_alloc security/security.c:171 [inline]
 security_file_alloc+0x34/0x310 security/security.c:2406
 init_file+0x90/0x2b0 fs/file_table.c:184
 alloc_empty_file+0x74/0x1d0 fs/file_table.c:266
 path_openat+0x10f/0x3860 fs/namei.c:4844
 do_file_open+0x23e/0x4a0 fs/namei.c:4887
 do_sys_openat2+0x113/0x200 fs/open.c:1364
 do_sys_open fs/open.c:1370 [inline]
 __do_sys_openat fs/open.c:1386 [inline]
 __se_sys_openat fs/open.c:1381 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1381
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88801bba9600: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff88801bba9680: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
>ffff88801bba9700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff88801bba9780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88801bba9800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================



	

	



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			2026/06/06 09:15
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			c93952cc0034
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			ci-upstream-net-this-kasan-gce
			KASAN: slab-use-after-free Read in sit_tunnel_xmit
		

		
		


* Struck through repros no longer work on HEAD.