Message-ID: <6847c3e5.050a0220.33aa0e.0305.GAE@google.com>
Date: Mon, 09 Jun 2025 22:34:29 -0700
From: syzbot <syzbot+1ec2f6a450f0b54af8c8@...kaller.appspotmail.com>
To: davem@...emloft.net, edumazet@...gle.com, horms@...nel.org, 
	kuba@...nel.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	pabeni@...hat.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] KASAN: use-after-free Read in __linkwatch_run_queue

syzbot has found a reproducer for the following issue on:

HEAD commit:    19272b37aa4f Linux 6.16-rc1
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11458d70580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2f8ce980f626e3f9
dashboard link: https://syzkaller.appspot.com/bug?extid=1ec2f6a450f0b54af8c8
compiler:       aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14af5a0c580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/fa3fbcfdac58/non_bootable_disk-19272b37.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6d42ad978905/vmlinux-19272b37.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9a19eed32f09/Image-19272b37.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1ec2f6a450f0b54af8c8@...kaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in __linkwatch_run_queue+0x180/0x2b8 net/core/link_watch.c:244
Read at addr faf00000113fca2d by task kworker/u8:2/40
Pointer tag: [fa], memory tag: [fe]

CPU: 0 UID: 0 PID: 40 Comm: kworker/u8:2 Not tainted 6.16.0-rc1-syzkaller #0 PREEMPT 
Hardware name: linux,dummy-virt (DT)
Workqueue: events_unbound linkwatch_event
Call trace:
 show_stack+0x18/0x24 arch/arm64/kernel/stacktrace.c:466 (C)
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x78/0x90 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0x108/0x630 mm/kasan/report.c:521
 kasan_report+0x88/0xac mm/kasan/report.c:634
 report_tag_fault arch/arm64/mm/fault.c:332 [inline]
 do_tag_recovery arch/arm64/mm/fault.c:344 [inline]
 __do_kernel_fault+0x170/0x1c8 arch/arm64/mm/fault.c:386
 do_bad_area arch/arm64/mm/fault.c:486 [inline]
 do_tag_check_fault+0x78/0x8c arch/arm64/mm/fault.c:843
 do_mem_abort+0x44/0x94 arch/arm64/mm/fault.c:919
 el1_abort+0x40/0x60 arch/arm64/kernel/entry-common.c:455
 el1h_64_sync_handler+0xa4/0x120 arch/arm64/kernel/entry-common.c:533
 el1h_64_sync+0x6c/0x70 arch/arm64/kernel/entry.S:595
 __linkwatch_run_queue+0x180/0x2b8 net/core/link_watch.c:244 (P)
 linkwatch_event+0x30/0x40 net/core/link_watch.c:304
 process_one_work+0x178/0x2cc kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3321 [inline]
 worker_thread+0x250/0x358 kernel/workqueue.c:3402
 kthread+0x130/0x1fc kernel/kthread.c:464
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:862

Freed by task 12:
 kasan_save_stack+0x3c/0x64 mm/kasan/common.c:47
 save_stack_info+0x40/0x158 mm/kasan/tags.c:106
 kasan_save_free_info+0x18/0x24 mm/kasan/tags.c:147
 poison_slab_object mm/kasan/common.c:247 [inline]
 __kasan_slab_free+0x74/0x8c mm/kasan/common.c:264
 kasan_slab_free include/linux/kasan.h:233 [inline]
 slab_free_hook mm/slub.c:2381 [inline]
 slab_free mm/slub.c:4643 [inline]
 kfree+0xfc/0x30c mm/slub.c:4842
 kvfree+0x3c/0x4c mm/slub.c:5058
 netdev_release+0x30/0x44 net/core/net-sysfs.c:2231
 device_release+0x34/0x90 drivers/base/core.c:2568
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0xa4/0x114 lib/kobject.c:737
 netdev_run_todo+0x1f0/0x5a0 net/core/dev.c:11412
 rtnl_unlock+0x10/0x1c net/core/rtnetlink.c:157
 default_device_exit_batch+0x320/0x394 net/core/dev.c:12645
 ops_exit_list net/core/net_namespace.c:206 [inline]
 ops_undo_list+0x10c/0x23c net/core/net_namespace.c:253
 cleanup_net+0x1f8/0x3d0 net/core/net_namespace.c:686
 process_one_work+0x178/0x2cc kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3321 [inline]
 worker_thread+0x250/0x358 kernel/workqueue.c:3402
 kthread+0x130/0x1fc kernel/kthread.c:464
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:862

The buggy address belongs to the object at fff00000113fc000
 which belongs to the cache kmalloc-cg-4k of size 4096
The buggy address is located 2605 bytes inside of
 4096-byte region [fff00000113fc000, fff00000113fd000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xfaf00000113fc000 pfn:0x513f8
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:fdf000001128ff81
flags: 0x1ffc00000000240(workingset|head|node=0|zone=0|lastcpupid=0x7ff|kasantag=0x0)
page_type: f5(slab)
raw: 01ffc00000000240 fdf0000003008000 ffffc1ffc0488e10 ffffc1ffc044f810
raw: faf00000113fc000 0000000000080004 00000000f5000000 fdf000001128ff81
head: 01ffc00000000240 fdf0000003008000 ffffc1ffc0488e10 ffffc1ffc044f810
head: faf00000113fc000 0000000000080004 00000000f5000000 fdf000001128ff81
head: 01ffc00000000003 ffffc1ffc044fe01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 fff00000113fc800: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
 fff00000113fc900: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
>fff00000113fca00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
                         ^
 fff00000113fcb00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
 fff00000113fcc00: fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe fe
==================================================================


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

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