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KASAN: use-after-free Read in __fib6_drop_pcpu_from

Status: premoderation: reported on 2026/04/12 19:12
Reported-by: syzbot+d51d997cb12667673614@syzkaller.appspotmail.com
First crash: 63d, last: 52d
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream general protection fault in __fib6_drop_pcpu_from (4) net 19 23 1627d 1934d 0/29 auto-closed as invalid on 2022/03/31 04:19
upstream general protection fault in __fib6_drop_pcpu_from (6) net 17 236 164d 496d 0/29 auto-obsoleted due to no activity on 2026/03/13 05:04
upstream general protection fault in __fib6_drop_pcpu_from (7) net 2 4 19d 50d 0/29 closed as invalid on 2026/05/30 06:16
upstream general protection fault in __fib6_drop_pcpu_from (5) net 8 467 726d 771d 26/29 fixed on 2024/06/18 11:11

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in __fib6_drop_pcpu_from+0x157/0x2e0 net/ipv6/ip6_fib.c:980
Read of size 8 at addr ffff88810ef35570 by task syz.0.1568/6188

CPU: 0 PID: 6188 Comm: syz.0.1568 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0xe2/0x130 mm/kasan/report.c:452
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309
 __fib6_drop_pcpu_from+0x157/0x2e0 net/ipv6/ip6_fib.c:980
 fib6_drop_pcpu_from net/ipv6/ip6_fib.c:1024 [inline]
 fib6_purge_rt+0x256/0x670 net/ipv6/ip6_fib.c:1035
 fib6_del_route net/ipv6/ip6_fib.c:1984 [inline]
 fib6_del+0xa62/0xfa0 net/ipv6/ip6_fib.c:2029
 fib6_clean_node+0x2a4/0x540 net/ipv6/ip6_fib.c:2191
 fib6_walk_continue+0x4fc/0x700 net/ipv6/ip6_fib.c:2113
 fib6_walk+0x153/0x290 net/ipv6/ip6_fib.c:2161
 fib6_clean_tree net/ipv6/ip6_fib.c:2241 [inline]
 __fib6_clean_all net/ipv6/ip6_fib.c:2257 [inline]
 fib6_clean_all+0x1b3/0x290 net/ipv6/ip6_fib.c:2268
 rt6_sync_down_dev net/ipv6/route.c:4794 [inline]
 rt6_disable_ip+0x121/0x6b0 net/ipv6/route.c:4799
 addrconf_ifdown+0x150/0x1850 net/ipv6/addrconf.c:3788
 addrconf_notify+0x3bd/0xe90 net/ipv6/addrconf.c:-1
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:410
 call_netdevice_notifiers_info net/core/dev.c:2054 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2066 [inline]
 call_netdevice_notifiers net/core/dev.c:2080 [inline]
 __dev_notify_flags+0x241/0x560 net/core/dev.c:8587
 dev_change_flags+0xe8/0x1a0 net/core/dev.c:8623
 do_setlink+0xc06/0x3e10 net/core/rtnetlink.c:2732
 rtnl_group_changelink net/core/rtnetlink.c:3251 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3420 [inline]
 rtnl_newlink+0xed0/0x18f0 net/core/rtnetlink.c:3530
 rtnetlink_rcv_msg+0xa31/0xcc0 net/core/rtnetlink.c:5610
 netlink_rcv_skb+0x1f5/0x440 net/netlink/af_netlink.c:2503
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5628
 netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
 netlink_unicast+0x876/0xa40 net/netlink/af_netlink.c:1340
 netlink_sendmsg+0x89c/0xb50 net/netlink/af_netlink.c:1914
 sock_sendmsg_nosec net/socket.c:652 [inline]
 __sock_sendmsg net/socket.c:664 [inline]
 ____sys_sendmsg+0x5b7/0x8f0 net/socket.c:2376
 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2430
 __sys_sendmsg net/socket.c:2459 [inline]
 __do_sys_sendmsg net/socket.c:2468 [inline]
 __se_sys_sendmsg net/socket.c:2466 [inline]
 __x64_sys_sendmsg+0x1f9/0x2c0 net/socket.c:2466
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f748cbb1819
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:00007f748b5eb028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f748ce2b090 RCX: 00007f748cbb1819
RDX: 0000000000000000 RSI: 0000200000000140 RDI: 000000000000000b
RBP: 00007f748cc47c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f748ce2b128 R14: 00007f748ce2b090 R15: 00007fffb0f06468

Allocated by task 5886:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:430 [inline]
 __kasan_slab_alloc+0xbd/0xf0 mm/kasan/common.c:463
 kasan_slab_alloc include/linux/kasan.h:244 [inline]
 slab_post_alloc_hook+0x5d/0x2f0 mm/slab.h:580
 slab_alloc_node mm/slub.c:2952 [inline]
 slab_alloc mm/slub.c:2960 [inline]
 kmem_cache_alloc+0x162/0x2d0 mm/slub.c:2965
 dst_alloc+0x176/0x4f0 net/core/dst.c:93
 ip6_dst_alloc net/ipv6/route.c:340 [inline]
 ip6_rt_pcpu_alloc net/ipv6/route.c:1371 [inline]
 rt6_make_pcpu_route net/ipv6/route.c:1420 [inline]
 ip6_pol_route+0x988/0x1170 net/ipv6/route.c:2264
 ip6_pol_route_input+0x56/0x80 net/ipv6/route.c:2285
 pol_lookup_func include/net/ip6_fib.h:594 [inline]
 __fib6_rule_action net/ipv6/fib6_rules.c:232 [inline]
 fib6_rule_action+0x1c7/0x710 net/ipv6/fib6_rules.c:270
 fib_rules_lookup+0x489/0x8e0 net/core/fib_rules.c:318
 fib6_rule_lookup+0x195/0x5d0 net/ipv6/fib6_rules.c:107
 ip6_route_input_lookup net/ipv6/route.c:2297 [inline]
 inet6_rtm_getroute+0xa10/0x13c0 net/ipv6/route.c:5983
 rtnetlink_rcv_msg+0x845/0xcc0 net/core/rtnetlink.c:5601
 netlink_rcv_skb+0x1f5/0x440 net/netlink/af_netlink.c:2503
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:5628
 netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
 netlink_unicast+0x876/0xa40 net/netlink/af_netlink.c:1340
 netlink_sendmsg+0x89c/0xb50 net/netlink/af_netlink.c:1914
 sock_sendmsg_nosec net/socket.c:652 [inline]
 __sock_sendmsg net/socket.c:664 [inline]
 sock_write_iter+0x2a6/0x3a0 net/socket.c:1018
 call_write_iter include/linux/fs.h:2066 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x758/0xdc0 fs/read_write.c:605
 ksys_write+0x149/0x250 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:667
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Freed by task 24:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x125/0x160 mm/kasan/common.c:362
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370
 kasan_slab_free include/linux/kasan.h:220 [inline]
 slab_free_hook mm/slub.c:1600 [inline]
 slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626
 slab_free mm/slub.c:3208 [inline]
 kmem_cache_free+0x100/0x2d0 mm/slub.c:3224
 dst_destroy+0x18a/0x240 net/core/dst.c:126
 dst_destroy_rcu+0x19/0x20 net/core/dst.c:139
 rcu_do_batch+0x4ef/0xab0 kernel/rcu/tree.c:2494
 rcu_core+0x577/0xd80 kernel/rcu/tree.c:2735
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2748
 __do_softirq+0x255/0x563 kernel/softirq.c:309

Last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 __call_rcu kernel/rcu/tree.c:2980 [inline]
 call_rcu+0x11a/0x10b0 kernel/rcu/tree.c:3054
 dst_release+0x123/0x190 net/core/dst.c:183
 refdst_drop include/net/dst.h:253 [inline]
 skb_dst_drop include/net/dst.h:265 [inline]
 skb_release_head_state+0x70/0x210 net/core/skbuff.c:664
 skb_release_all net/core/skbuff.c:678 [inline]
 __kfree_skb net/core/skbuff.c:694 [inline]
 kfree_skb+0x89/0x2f0 net/core/skbuff.c:713
 skb_queue_purge+0x12f/0x1b0 net/core/skbuff.c:3194
 netlink_sock_destruct+0x27/0x190 net/netlink/af_netlink.c:387
 __sk_destruct+0x53/0x600 net/core/sock.c:1818
 sk_destruct net/core/sock.c:1863 [inline]
 __sk_free+0x313/0x410 net/core/sock.c:1874
 sk_free+0x54/0x90 net/core/sock.c:1885
 deferred_put_nlk_sk+0xa6/0xe0 net/netlink/af_netlink.c:715
 rcu_do_batch+0x4ef/0xab0 kernel/rcu/tree.c:2494
 rcu_core+0x577/0xd80 kernel/rcu/tree.c:2735
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2748
 __do_softirq+0x255/0x563 kernel/softirq.c:309

The buggy address belongs to the object at ffff88810ef35500
 which belongs to the cache ip6_dst_cache of size 240
The buggy address is located 112 bytes inside of
 240-byte region [ffff88810ef35500, ffff88810ef355f0)
The buggy address belongs to the page:
page:ffffea00043bcd40 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10ef35
flags: 0x4000000000000200(slab)
raw: 4000000000000200 dead000000000100 dead000000000122 ffff88810c334000
raw: 0000000000000000 00000000000c000c 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x112a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_HARDWALL), pid 0, ts 249068200217, free_ts 226833786374
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x179/0x180 mm/page_alloc.c:2462
 get_page_from_freelist+0x223b/0x23d0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x290/0x620 mm/page_alloc.c:5384
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1813 [inline]
 new_slab+0x84/0x3f0 mm/slub.c:1874
 new_slab_objects mm/slub.c:2632 [inline]
 ___slab_alloc+0x2a6/0x450 mm/slub.c:2796
 __slab_alloc+0x63/0xa0 mm/slub.c:2836
 slab_alloc_node mm/slub.c:2918 [inline]
 slab_alloc mm/slub.c:2960 [inline]
 kmem_cache_alloc+0x1ac/0x2d0 mm/slub.c:2965
 dst_alloc+0x176/0x4f0 net/core/dst.c:93
 ip6_dst_alloc net/ipv6/route.c:340 [inline]
 icmp6_dst_alloc+0xf5/0x560 net/ipv6/route.c:3170
 ndisc_send_skb+0x293/0xbe0 net/ipv6/ndisc.c:493
 ndisc_send_rs+0x6e5/0x960 net/ipv6/ndisc.c:707
 addrconf_rs_timer+0x2cf/0x610 net/ipv6/addrconf.c:3968
 call_timer_fn+0x38/0x290 kernel/time/timer.c:1450
 expire_timers kernel/time/timer.c:1495 [inline]
 __run_timers+0x650/0x9e0 kernel/time/timer.c:1789
 run_timer_softirq+0x6a/0xf0 kernel/time/timer.c:1802
 __do_softirq+0x255/0x563 kernel/softirq.c:309
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:28 [inline]
 free_pages_prepare mm/page_alloc.c:1349 [inline]
 free_pcp_prepare mm/page_alloc.c:1421 [inline]
 free_unref_page_prepare+0x2b7/0x2d0 mm/page_alloc.c:3336
 free_unref_page mm/page_alloc.c:3391 [inline]
 free_the_page mm/page_alloc.c:5443 [inline]
 __free_pages+0x146/0x3b0 mm/page_alloc.c:5454
 __vunmap+0x86d/0x9f0 mm/vmalloc.c:2307
 free_work+0x5a/0x80 mm/vmalloc.c:69
 process_one_work+0x6e1/0xba0 kernel/workqueue.c:2301
 worker_thread+0xa6a/0x13c0 kernel/workqueue.c:2447
 kthread+0x346/0x3d0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

Memory state around the buggy address:
 ffff88810ef35400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810ef35480: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
>ffff88810ef35500: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                             ^
 ffff88810ef35580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc
 ffff88810ef35600: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/23 18:40 android13-5.10-lts d8c55bf860fd 4c3406dc .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in __fib6_drop_pcpu_from
2026/04/12 19:11 android13-5.10-lts cc0ae2abdc73 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in __fib6_drop_pcpu_from
* Struck through repros no longer work on HEAD.