Subject: Re: [syzbot] [net?] KASAN: slab-use-after-free Read in l2tp_tunnel_del_work

From: syzbot <[email-masked]>
Date: Mon, 01 Jul 2024 09:12:21 -0700

syzbot has found a reproducer for the following issue on:

HEAD commit:    1c5fc27bc48a Merge tag 'nf-next-24-06-28' of git://git.ker..
git tree:       net-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=161d2066980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5264b58fdff6e881
dashboard link: https://syzkaller.appspot.com/bug?extid=b471b7c936301a59745b
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1094f701980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16bf2361980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9672225af907/disk-1c5fc27b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0f14d163a914/vmlinux-1c5fc27b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ec6c331e6a6e/bzImage-1c5fc27b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

==================================================================
BUG: KASAN: slab-use-after-free in l2tp_tunnel_del_work+0xe5/0x330 net/l2tp/l2tp_core.c:1334
Read of size 8 at addr ffff88802361a0b8 by task kworker/u8:1/12

CPU: 1 PID: 12 Comm: kworker/u8:1 Not tainted 6.10.0-rc5-syzkaller-01137-g1c5fc27bc48a #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
Workqueue: l2tp l2tp_tunnel_del_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0x169/0x550 mm/kasan/report.c:488
 kasan_report+0x143/0x180 mm/kasan/report.c:601
 l2tp_tunnel_del_work+0xe5/0x330 net/l2tp/l2tp_core.c:1334
 process_one_work kernel/workqueue.c:3248 [inline]
 process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3329
 worker_thread+0x86d/0xd50 kernel/workqueue.c:3409
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

Allocated by task 5102:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
 poison_kmalloc_redzone mm/kasan/common.c:370 [inline]
 __kasan_kmalloc+0x98/0xb0 mm/kasan/common.c:387
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slub.c:4123 [inline]
 __kmalloc_noprof+0x1f9/0x400 mm/slub.c:4136
 kmalloc_noprof include/linux/slab.h:664 [inline]
 kzalloc_noprof include/linux/slab.h:778 [inline]
 l2tp_session_create+0x3b/0xc20 net/l2tp/l2tp_core.c:1675
 pppol2tp_connect+0xca3/0x17a0 net/l2tp/l2tp_ppp.c:782
 __sys_connect_file net/socket.c:2049 [inline]
 __sys_connect+0x2df/0x310 net/socket.c:2066
 __do_sys_connect net/socket.c:2076 [inline]
 __se_sys_connect net/socket.c:2073 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2073
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 0:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:579
 poison_slab_object+0xe0/0x150 mm/kasan/common.c:240
 __kasan_slab_free+0x37/0x60 mm/kasan/common.c:256
 kasan_slab_free include/linux/kasan.h:184 [inline]
 slab_free_hook mm/slub.c:2196 [inline]
 slab_free mm/slub.c:4438 [inline]
 kfree+0x149/0x360 mm/slub.c:4559
 __sk_destruct+0x58/0x5f0 net/core/sock.c:2191
 rcu_do_batch kernel/rcu/tree.c:2535 [inline]
 rcu_core+0xafd/0x1830 kernel/rcu/tree.c:2809
 handle_softirqs+0x2c4/0x970 kernel/softirq.c:554
 __do_softirq kernel/softirq.c:588 [inline]
 invoke_softirq kernel/softirq.c:428 [inline]
 __irq_exit_rcu+0xf4/0x1c0 kernel/softirq.c:637
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:649
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1043
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702

Last potentially related work creation:
 kasan_save_stack+0x3f/0x60 mm/kasan/common.c:47
 __kasan_record_aux_stack+0xac/0xc0 mm/kasan/generic.c:541
 __call_rcu_common kernel/rcu/tree.c:3072 [inline]
 call_rcu+0x167/0xa70 kernel/rcu/tree.c:3176
 pppol2tp_release+0x24b/0x350 net/l2tp/l2tp_ppp.c:457
 __sock_release net/socket.c:659 [inline]
 sock_close+0xbc/0x240 net/socket.c:1421
 __fput+0x406/0x8b0 fs/file_table.c:422
 task_work_run+0x24f/0x310 kernel/task_work.c:180
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xa27/0x27e0 kernel/exit.c:874
 do_group_exit+0x207/0x2c0 kernel/exit.c:1023
 __do_sys_exit_group kernel/exit.c:1034 [inline]
 __se_sys_exit_group kernel/exit.c:1032 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1032
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88802361a000
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 184 bytes inside of
 freed 1024-byte region [ffff88802361a000, ffff88802361a400)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x23618
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffefff(slab)
raw: 00fff00000000040 ffff888015041dc0 ffffea00008d3400 0000000000000002
raw: 0000000000000000 0000000080100010 00000001ffffefff 0000000000000000
head: 00fff00000000040 ffff888015041dc0 ffffea00008d3400 0000000000000002
head: 0000000000000000 0000000080100010 00000001ffffefff 0000000000000000
head: 00fff00000000003 ffffea00008d8601 ffffffffffffffff 0000000000000000
head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 4757, tgid 4757 (S41dhcpcd), ts 76204097888, free_ts 76202473642
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f3/0x230 mm/page_alloc.c:1473
 prep_new_page mm/page_alloc.c:1481 [inline]
 get_page_from_freelist+0x2e4c/0x2f10 mm/page_alloc.c:3425
 __alloc_pages_noprof+0x256/0x6c0 mm/page_alloc.c:4683
 __alloc_pages_node_noprof include/linux/gfp.h:269 [inline]
 alloc_pages_node_noprof include/linux/gfp.h:296 [inline]
 alloc_slab_page+0x5f/0x120 mm/slub.c:2265
 allocate_slab+0x5a/0x2f0 mm/slub.c:2428
 new_slab mm/slub.c:2481 [inline]
 ___slab_alloc+0xcd1/0x14b0 mm/slub.c:3667
 __slab_alloc+0x58/0xa0 mm/slub.c:3757
 __slab_alloc_node mm/slub.c:3810 [inline]
 slab_alloc_node mm/slub.c:3990 [inline]
 __do_kmalloc_node mm/slub.c:4122 [inline]
 __kmalloc_noprof+0x257/0x400 mm/slub.c:4136
 kmalloc_noprof include/linux/slab.h:664 [inline]
 kzalloc_noprof include/linux/slab.h:778 [inline]
 tomoyo_init_log+0x1b3e/0x2050 security/tomoyo/audit.c:275
 tomoyo_supervisor+0x38a/0x11f0 security/tomoyo/common.c:2089
 tomoyo_audit_env_log security/tomoyo/environ.c:36 [inline]
 tomoyo_env_perm+0x178/0x210 security/tomoyo/environ.c:63
 tomoyo_environ security/tomoyo/domain.c:672 [inline]
 tomoyo_find_next_domain+0x1384/0x1cf0 security/tomoyo/domain.c:878
 tomoyo_bprm_check_security+0x115/0x180 security/tomoyo/tomoyo.c:102
 security_bprm_check+0x65/0x90 security/security.c:1191
 search_binary_handler fs/exec.c:1785 [inline]
 exec_binprm fs/exec.c:1839 [inline]
 bprm_execve+0xa56/0x17c0 fs/exec.c:1891
 do_execveat_common+0x553/0x700 fs/exec.c:1998
page last free pid 4757 tgid 4757 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1093 [inline]
 free_unref_page+0xd22/0xea0 mm/page_alloc.c:2588
 __slab_free+0x31b/0x3d0 mm/slub.c:4349
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x9e/0x140 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x14f/0x170 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x23/0x80 mm/kasan/common.c:322
 kasan_slab_alloc include/linux/kasan.h:201 [inline]
 slab_post_alloc_hook mm/slub.c:3940 [inline]
 slab_alloc_node mm/slub.c:4002 [inline]
 __do_kmalloc_node mm/slub.c:4122 [inline]
 __kmalloc_noprof+0x1a3/0x400 mm/slub.c:4136
 kmalloc_noprof include/linux/slab.h:664 [inline]
 tomoyo_add_entry security/tomoyo/common.c:2023 [inline]
 tomoyo_supervisor+0xe0d/0x11f0 security/tomoyo/common.c:2095
 tomoyo_audit_env_log security/tomoyo/environ.c:36 [inline]
 tomoyo_env_perm+0x178/0x210 security/tomoyo/environ.c:63
 tomoyo_environ security/tomoyo/domain.c:672 [inline]
 tomoyo_find_next_domain+0x1384/0x1cf0 security/tomoyo/domain.c:878
 tomoyo_bprm_check_security+0x115/0x180 security/tomoyo/tomoyo.c:102
 security_bprm_check+0x65/0x90 security/security.c:1191
 search_binary_handler fs/exec.c:1785 [inline]
 exec_binprm fs/exec.c:1839 [inline]
 bprm_execve+0xa56/0x17c0 fs/exec.c:1891
 do_execveat_common+0x553/0x700 fs/exec.c:1998
 do_execve fs/exec.c:2072 [inline]
 __do_sys_execve fs/exec.c:2148 [inline]
 __se_sys_execve fs/exec.c:2143 [inline]
 __x64_sys_execve+0x92/0xb0 fs/exec.c:2143
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888023619f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802361a000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88802361a080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                        ^
 ffff88802361a100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88802361a180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

---
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