[syzbot] [bluetooth?] KASAN: slab-use-after-free Read in skb_pull

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d13f3ac64efb Merge tag 'mips-fixes_6.18_1' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=171bd8b4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=14b6a9313e132a6b
dashboard link: https://syzkaller.appspot.com/bug?extid=2d7ca98b34b871173f28
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/7bcabeb5eac8/disk-d13f3ac6.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f32f75375954/vmlinux-d13f3ac6.xz
kernel image: https://storage.googleapis.com/syzbot-assets/889beba59370/bzImage-d13f3ac6.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2d7ca9...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in skb_pull_inline include/linux/skbuff.h:2839 [inline]
BUG: KASAN: slab-use-after-free in skb_pull+0x133/0x1d0 net/core/skbuff.c:2619
Read of size 4 at addr ffff8880687ace30 by task kworker/0:1/16647

CPU: 0 UID: 0 PID: 16647 Comm: kworker/0:1 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events hci_uart_write_work
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
skb_pull_inline include/linux/skbuff.h:2839 [inline]
skb_pull+0x133/0x1d0 net/core/skbuff.c:2619
hci_uart_write_work+0x329/0x550 drivers/bluetooth/hci_ldisc.c:168
process_one_work kernel/workqueue.c:3263 [inline]
process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 16739:
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+0x112/0x2d0 net/core/skbuff.c:660
alloc_skb include/linux/skbuff.h:1383 [inline]
bt_skb_alloc include/net/bluetooth/bluetooth.h:510 [inline]
hci_cmd_sync_alloc+0x3d/0x380 net/bluetooth/hci_sync.c:58
hci_cmd_sync_add net/bluetooth/hci_sync.c:99 [inline]
__hci_cmd_sync_sk+0x1a7/0xbc0 net/bluetooth/hci_sync.c:168
__hci_cmd_sync_status_sk net/bluetooth/hci_sync.c:263 [inline]
__hci_cmd_sync_status net/bluetooth/hci_sync.c:287 [inline]
hci_read_local_features_sync net/bluetooth/hci_sync.c:3708 [inline]
hci_init_stage_sync net/bluetooth/hci_sync.c:3623 [inline]
hci_init1_sync net/bluetooth/hci_sync.c:3755 [inline]
hci_init_sync net/bluetooth/hci_sync.c:4867 [inline]
hci_dev_init_sync net/bluetooth/hci_sync.c:5059 [inline]
hci_dev_open_sync+0x14be/0x2b60 net/bluetooth/hci_sync.c:5137
hci_dev_do_open net/bluetooth/hci_core.c:430 [inline]
hci_power_on+0x1b4/0x680 net/bluetooth/hci_core.c:959
process_one_work kernel/workqueue.c:3263 [inline]
process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff8880687acdc0
which belongs to the cache skbuff_head_cache of size 240
The buggy address is located 112 bytes inside of
freed 240-byte region [ffff8880687acdc0, ffff8880687aceb0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x687ac
memcg:ffff88806bd25281
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88801d2fb8c0 dead000000000100 dead000000000122
raw: 0000000000000000 00000000000c000c 00000000f5000000 ffff88806bd25281
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x52820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 6067, tgid 6067 (kworker/u8:10), ts 1088046828849, free_ts 1087965340429
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+0x112/0x2d0 net/core/skbuff.c:660
alloc_skb include/linux/skbuff.h:1383 [inline]
nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:763 [inline]
nsim_dev_trap_report drivers/net/netdevsim/dev.c:820 [inline]
nsim_dev_trap_report_work+0x29a/0xb80 drivers/net/netdevsim/dev.c:866
process_one_work kernel/workqueue.c:3263 [inline]
process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
page last free pid 5194 tgid 5194 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
__tlb_remove_table_free mm/mmu_gather.c:227 [inline]
tlb_remove_table_rcu+0x85/0x100 mm/mmu_gather.c:290
rcu_do_batch kernel/rcu/tree.c:2605 [inline]
rcu_core+0xcab/0x1770 kernel/rcu/tree.c:2861
handle_softirqs+0x286/0x870 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:723
irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
common_interrupt+0xbb/0xe0 arch/x86/kernel/irq.c:318
asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:688

Memory state around the buggy address:
ffff8880687acd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc
ffff8880687acd80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>ffff8880687ace00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880687ace80: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
ffff8880687acf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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