[v5.15] KASAN: use-after-free Read in __ip6_del_rt

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0c935c049b5c Linux 5.15.179
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=100e064c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=98c228fbc016eb3a
dashboard link: https://syzkaller.appspot.com/bug?extid=5afee0faa2fb77bb8011
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d5477072f336/disk-0c935c04.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/77d15907ffb3/vmlinux-0c935c04.xz
kernel image: https://storage.googleapis.com/syzbot-assets/efe5d79cb16a/Image-0c935c04.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5afee0...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in __lock_acquire+0x114/0x7638 kernel/locking/lockdep.c:4882
Read of size 8 at addr ffff0000d5f3c430 by task kworker/u4:9/4282

CPU: 0 PID: 4282 Comm: kworker/u4:9 Not tainted 5.15.179-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Workqueue: netns cleanup_net
Call trace:
dump_backtrace+0x0/0x530 arch/arm64/kernel/stacktrace.c:152
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x108/0x170 lib/dump_stack.c:106
print_address_description+0x7c/0x3f0 mm/kasan/report.c:248
__kasan_report mm/kasan/report.c:434 [inline]
kasan_report+0x174/0x1e4 mm/kasan/report.c:451
__asan_report_load8_noabort+0x44/0x50 mm/kasan/report_generic.c:309
__lock_acquire+0x114/0x7638 kernel/locking/lockdep.c:4882
lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
_raw_spin_lock_bh+0x124/0x1c4 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:368 [inline]
__ip6_del_rt+0x90/0x18c net/ipv6/route.c:3884
ip6_del_rt+0xdc/0x13c net/ipv6/route.c:3900
__remove_nexthop_fib net/ipv4/nexthop.c:1860 [inline]
__remove_nexthop+0x244/0x173c net/ipv4/nexthop.c:1868
remove_nexthop+0x80/0x1b4 net/ipv4/nexthop.c:1894
remove_nh_grp_entry net/ipv4/nexthop.c:1750 [inline]
remove_nexthop_from_groups net/ipv4/nexthop.c:1815 [inline]
__remove_nexthop+0x8e8/0x173c net/ipv4/nexthop.c:1879
remove_nexthop+0x80/0x1b4 net/ipv4/nexthop.c:1894
flush_all_nexthops net/ipv4/nexthop.c:2405 [inline]
nexthop_net_exit+0x4c/0xc0 net/ipv4/nexthop.c:3728
ops_exit_list net/core/net_namespace.c:172 [inline]
cleanup_net+0x644/0xa9c net/core/net_namespace.c:618
process_one_work+0x790/0x11b8 kernel/workqueue.c:2310
worker_thread+0x910/0x1034 kernel/workqueue.c:2457
kthread+0x37c/0x45c kernel/kthread.c:334
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:870

Allocated by task 4021:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:434 [inline]
____kasan_kmalloc+0xbc/0xfc mm/kasan/common.c:513
__kasan_kmalloc+0x10/0x1c mm/kasan/common.c:522
kasan_kmalloc include/linux/kasan.h:264 [inline]
kmem_cache_alloc_trace+0x27c/0x47c mm/slub.c:3247
kmalloc include/linux/slab.h:591 [inline]
kzalloc include/linux/slab.h:721 [inline]
fib6_net_init+0x1f8/0x6c8 net/ipv6/ip6_fib.c:2382
ops_init+0x2e4/0x54c net/core/net_namespace.c:138
setup_net+0x378/0xa64 net/core/net_namespace.c:333
copy_net_ns+0x2f8/0x5e0 net/core/net_namespace.c:486
create_new_namespaces+0x330/0x61c kernel/nsproxy.c:110
unshare_nsproxy_namespaces+0x108/0x158 kernel/nsproxy.c:226
ksys_unshare+0x424/0x7e4 kernel/fork.c:3099
__do_sys_unshare kernel/fork.c:3173 [inline]
__se_sys_unshare kernel/fork.c:3171 [inline]
__arm64_sys_unshare+0x3c/0x50 kernel/fork.c:3171
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

Freed by task 4282:
kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track+0x4c/0x84 mm/kasan/common.c:46
kasan_set_free_info+0x28/0x4c mm/kasan/generic.c:360
____kasan_slab_free+0x118/0x164 mm/kasan/common.c:366
__kasan_slab_free+0x18/0x28 mm/kasan/common.c:374
kasan_slab_free include/linux/kasan.h:230 [inline]
slab_free_hook mm/slub.c:1705 [inline]
slab_free_freelist_hook+0x128/0x1ec mm/slub.c:1731
slab_free mm/slub.c:3499 [inline]
kfree+0x178/0x410 mm/slub.c:4559
fib6_free_table net/ipv6/ip6_fib.c:215 [inline]
fib6_net_exit+0x1f0/0x274 net/ipv6/ip6_fib.c:2436
ops_exit_list net/core/net_namespace.c:172 [inline]
cleanup_net+0x644/0xa9c net/core/net_namespace.c:618
process_one_work+0x790/0x11b8 kernel/workqueue.c:2310
worker_thread+0x910/0x1034 kernel/workqueue.c:2457
kthread+0x37c/0x45c kernel/kthread.c:334
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:870

The buggy address belongs to the object at ffff0000d5f3c400
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 48 bytes inside of
512-byte region [ffff0000d5f3c400, ffff0000d5f3c600)
The buggy address belongs to the page:
page:0000000082854e45 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff0000d5f3e800 pfn:0x115f3c
head:0000000082854e45 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x5ffc00000010200(slab|head|node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000010200 fffffc0003a1cc08 fffffc00032dd608 ffff0000c0002600
raw: ffff0000d5f3e800 000000000010000f 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff0000d5f3c300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff0000d5f3c380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff0000d5f3c400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff0000d5f3c480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff0000d5f3c500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.