[v6.1] KASAN: use-after-free Read in __lock_sock

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3594f306da12 Linux 6.1.147
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1760bcf0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=30b8ca4950f83e04
dashboard link: https://syzkaller.appspot.com/bug?extid=b423ccad058be263094e
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17b0ff82580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13704aa2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/688153744f3f/disk-3594f306.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bed731de048a/vmlinux-3594f306.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f514506edb44/bzImage-3594f306.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b423cc...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in __lock_acquire+0xf7/0x7c50 kernel/locking/lockdep.c:4919
Read of size 8 at addr ffff8880691c00b0 by task kworker/u4:0/9

CPU: 1 PID: 9 Comm: kworker/u4:0 Not tainted 6.1.147-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: kkcmd kcm_tx_work
Call Trace:
<TASK>
dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
print_address_description mm/kasan/report.c:316 [inline]
print_report+0xa8/0x200 mm/kasan/report.c:418
kasan_report+0x10b/0x140 mm/kasan/report.c:522
__lock_acquire+0xf7/0x7c50 kernel/locking/lockdep.c:4919
lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
__raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
_raw_spin_lock_bh+0x32/0x50 kernel/locking/spinlock.c:178
spin_lock_bh include/linux/spinlock.h:356 [inline]
__lock_sock+0x152/0x2a0 net/core/sock.c:2916
lock_sock_nested+0x9b/0x100 net/core/sock.c:3493
lock_sock include/net/sock.h:1756 [inline]
kcm_tx_work+0x2d/0x180 net/kcm/kcmsock.c:731
process_one_work+0x898/0x1160 kernel/workqueue.c:2292
worker_thread+0xaa2/0x1250 kernel/workqueue.c:2439
kthread+0x29d/0x330 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>

Allocated by task 4641:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
__kasan_slab_alloc+0x6b/0x80 mm/kasan/common.c:328
kasan_slab_alloc include/linux/kasan.h:201 [inline]
slab_post_alloc_hook+0x4b/0x480 mm/slab.h:737
slab_alloc_node mm/slub.c:3398 [inline]
slab_alloc mm/slub.c:3406 [inline]
__kmem_cache_alloc_lru mm/slub.c:3413 [inline]
kmem_cache_alloc+0x123/0x2f0 mm/slub.c:3422
sk_prot_alloc+0x57/0x210 net/core/sock.c:2044
sk_alloc+0x36/0x340 net/core/sock.c:2103
kcm_clone net/kcm/kcmsock.c:1640 [inline]
kcm_ioctl+0x211/0xff0 net/kcm/kcmsock.c:1685
sock_do_ioctl+0xd3/0x2f0 net/socket.c:1204
sock_ioctl+0x4ed/0x6e0 net/socket.c:1321
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 4642:
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
kasan_save_free_info+0x2d/0x50 mm/kasan/generic.c:516
____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:236
kasan_slab_free include/linux/kasan.h:177 [inline]
slab_free_hook mm/slub.c:1724 [inline]
slab_free_freelist_hook+0x131/0x1a0 mm/slub.c:1750
slab_free mm/slub.c:3661 [inline]
kmem_cache_free+0xf7/0x290 mm/slub.c:3683
sk_prot_free net/core/sock.c:2084 [inline]
__sk_destruct+0x48d/0x630 net/core/sock.c:2172
kcm_release+0x520/0x5b0 net/kcm/kcmsock.c:1860
__sock_release net/socket.c:654 [inline]
sock_close+0xd5/0x240 net/socket.c:1400
__fput+0x22c/0x920 fs/file_table.c:320
task_work_run+0x1ca/0x250 kernel/task_work.c:203
resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
exit_to_user_mode_prepare+0xb1/0x140 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87
entry_SYSCALL_64_after_hwframe+0x68/0xd2

Last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:45
__kasan_record_aux_stack+0xb2/0xc0 mm/kasan/generic.c:486
insert_work+0x54/0x3c0 kernel/workqueue.c:1361
__queue_work+0xba3/0xfb0 kernel/workqueue.c:1520
queue_work_on+0x11d/0x1d0 kernel/workqueue.c:1548
queue_work include/linux/workqueue.h:512 [inline]
kcm_unattach+0x861/0xe80 net/kcm/kcmsock.c:1549
kcm_unattach_ioctl net/kcm/kcmsock.c:1606 [inline]
kcm_ioctl+0x78d/0xff0 net/kcm/kcmsock.c:1673
sock_do_ioctl+0xd3/0x2f0 net/socket.c:1204
sock_ioctl+0x4ed/0x6e0 net/socket.c:1321
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

Second to last potentially related work creation:
kasan_save_stack+0x3a/0x60 mm/kasan/common.c:45
__kasan_record_aux_stack+0xb2/0xc0 mm/kasan/generic.c:486
insert_work+0x54/0x3c0 kernel/workqueue.c:1361
__queue_work+0xba3/0xfb0 kernel/workqueue.c:1520
queue_work_on+0x11d/0x1d0 kernel/workqueue.c:1548
kcm_attach net/kcm/kcmsock.c:1429 [inline]
kcm_attach_ioctl net/kcm/kcmsock.c:1457 [inline]
kcm_ioctl+0xe4b/0xff0 net/kcm/kcmsock.c:1663
sock_do_ioctl+0xd3/0x2f0 net/socket.c:1204
sock_ioctl+0x4ed/0x6e0 net/socket.c:1321
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff8880691c0000
which belongs to the cache KCM of size 1720
The buggy address is located 176 bytes inside of
1720-byte region [ffff8880691c0000, ffff8880691c06b8)

The buggy address belongs to the physical page:
page:ffffea0001a47000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x691c0
head:ffffea0001a47000 order:3 compound_mapcount:0 compound_pincount:0
memcg:ffff888024240a01
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000122 ffff88814cc27640
raw: 0000000000000000 0000000080110011 00000001ffffffff ffff888024240a01
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 4641, tgid 4639 (syz.0.68), ts 135496927542, free_ts 85585135204
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2532
prep_new_page mm/page_alloc.c:2539 [inline]
get_page_from_freelist+0x1a26/0x1ac0 mm/page_alloc.c:4328
__alloc_pages+0x1df/0x4e0 mm/page_alloc.c:5614
alloc_slab_page+0x5d/0x160 mm/slub.c:1794
allocate_slab mm/slub.c:1939 [inline]
new_slab+0x87/0x2c0 mm/slub.c:1992
___slab_alloc+0xbc6/0x1220 mm/slub.c:3180
__slab_alloc mm/slub.c:3279 [inline]
slab_alloc_node mm/slub.c:3364 [inline]
slab_alloc mm/slub.c:3406 [inline]
__kmem_cache_alloc_lru mm/slub.c:3413 [inline]
kmem_cache_alloc+0x1b7/0x2f0 mm/slub.c:3422
sk_prot_alloc+0x57/0x210 net/core/sock.c:2044
sk_alloc+0x36/0x340 net/core/sock.c:2103
kcm_clone net/kcm/kcmsock.c:1640 [inline]
kcm_ioctl+0x211/0xff0 net/kcm/kcmsock.c:1685
sock_do_ioctl+0xd3/0x2f0 net/socket.c:1204
sock_ioctl+0x4ed/0x6e0 net/socket.c:1321
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1459 [inline]
free_pcp_prepare mm/page_alloc.c:1509 [inline]
free_unref_page_prepare+0x8b4/0x9a0 mm/page_alloc.c:3384
free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3479
kasan_depopulate_vmalloc_pte+0x67/0x80 mm/kasan/shadow.c:375
apply_to_pte_range mm/memory.c:2662 [inline]
apply_to_pmd_range mm/memory.c:2706 [inline]
apply_to_pud_range mm/memory.c:2742 [inline]
apply_to_p4d_range mm/memory.c:2778 [inline]
__apply_to_page_range+0x962/0xc80 mm/memory.c:2814
kasan_release_vmalloc+0x93/0xb0 mm/kasan/shadow.c:492
__purge_vmap_area_lazy+0xdb0/0x1900 mm/vmalloc.c:1782
drain_vmap_area_work+0x3c/0xd0 mm/vmalloc.c:1811
process_one_work+0x898/0x1160 kernel/workqueue.c:2292
worker_thread+0xaa2/0x1250 kernel/workqueue.c:2439
kthread+0x29d/0x330 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

Memory state around the buggy address:
ffff8880691bff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880691c0000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880691c0080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880691c0100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880691c0180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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