Subject: [syzbot] [net?] KASAN: slab-use-after-free Read in sock_def_readable (2)

From: syzbot <[email-masked]>
Date: Sun, 08 Mar 2026 06:42:35 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    6de23f81a5e0 Linux 7.0-rc1
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=148d655a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3b4642149033fe7c
dashboard link: https://syzkaller.appspot.com/bug?extid=f50072212ab792c86925
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1085e55a580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12e6d9e6580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-6de23f81.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5258f38d5768/vmlinux-6de23f81.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a7730b97aa5a/bzImage-6de23f81.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 list_empty include/linux/list.h:381 [inline]
BUG: KASAN: slab-use-after-free in waitqueue_active include/linux/wait.h:127 [inline]
BUG: KASAN: slab-use-after-free in wq_has_sleeper include/linux/wait.h:161 [inline]
BUG: KASAN: slab-use-after-free in skwq_has_sleeper include/net/sock.h:2404 [inline]
BUG: KASAN: slab-use-after-free in sock_def_readable+0x1cb/0x580 net/core/sock.c:3610
Read of size 8 at addr ffff888047cb0c00 by task kworker/0:4/5308

CPU: 0 UID: 0 PID: 5308 Comm: kworker/0:4 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: mld mld_ifc_work
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 list_empty include/linux/list.h:381 [inline]
 waitqueue_active include/linux/wait.h:127 [inline]
 wq_has_sleeper include/linux/wait.h:161 [inline]
 skwq_has_sleeper include/net/sock.h:2404 [inline]
 sock_def_readable+0x1cb/0x580 net/core/sock.c:3610
 send_to_lecd+0x322/0x600 net/atm/lec.c:538
 lec_arp_resolve net/atm/lec.c:1787 [inline]
 lec_start_xmit+0xec0/0x2660 net/atm/lec.c:285
 __netdev_start_xmit include/linux/netdevice.h:5275 [inline]
 netdev_start_xmit include/linux/netdevice.h:5284 [inline]
 xmit_one net/core/dev.c:3871 [inline]
 dev_hard_start_xmit+0x2d8/0x870 net/core/dev.c:3887
 sch_direct_xmit+0x251/0x4c0 net/sched/sch_generic.c:347
 __dev_xmit_skb net/core/dev.c:4186 [inline]
 __dev_queue_xmit+0x1538/0x38a0 net/core/dev.c:4802
 __ip6_finish_output net/ipv6/ip6_output.c:-1 [inline]
 ip6_finish_output+0x25c/0x610 net/ipv6/ip6_output.c:219
 NF_HOOK_COND include/linux/netfilter.h:307 [inline]
 ip6_output+0x340/0x550 net/ipv6/ip6_output.c:246
 NF_HOOK+0xa2/0x3a0 include/linux/netfilter.h:318
 mld_sendpack+0x8b4/0xe40 net/ipv6/mcast.c:1855
 mld_send_cr net/ipv6/mcast.c:2154 [inline]
 mld_ifc_work+0x835/0xe70 net/ipv6/mcast.c:2693
 process_one_work kernel/workqueue.c:3275 [inline]
 process_scheduled_works+0xb02/0x1830 kernel/workqueue.c:3358
 worker_thread+0xa50/0xfc0 kernel/workqueue.c:3439
 kthread+0x388/0x470 kernel/kthread.c:467
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Allocated by task 6850:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 unpoison_slab_object mm/kasan/common.c:340 [inline]
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4501 [inline]
 slab_alloc_node mm/slub.c:4830 [inline]
 kmem_cache_alloc_lru_noprof+0x2b8/0x640 mm/slub.c:4849
 sock_alloc_inode+0x28/0xc0 net/socket.c:322
 alloc_inode+0x6a/0x1b0 fs/inode.c:347
 new_inode_pseudo include/linux/fs.h:3003 [inline]
 sock_alloc net/socket.c:637 [inline]
 __sock_create+0x12d/0x9d0 net/socket.c:1569
 sock_create net/socket.c:1663 [inline]
 __sys_socket_create net/socket.c:1700 [inline]
 __sys_socket+0xd6/0x1b0 net/socket.c:1747
 __do_sys_socket net/socket.c:1761 [inline]
 __se_sys_socket net/socket.c:1759 [inline]
 __x64_sys_socket+0x7a/0x90 net/socket.c:1759
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6859:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2687 [inline]
 slab_free mm/slub.c:6124 [inline]
 kmem_cache_free+0x187/0x630 mm/slub.c:6254
 rcu_do_batch kernel/rcu/tree.c:2617 [inline]
 rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
 handle_softirqs+0x22a/0x870 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x5f/0x150 kernel/softirq.c:723
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1056
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697

Last potentially related work creation:
 kasan_save_stack+0x3e/0x60 mm/kasan/common.c:57
 kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:556
 __call_rcu_common kernel/rcu/tree.c:3131 [inline]
 call_rcu+0xee/0x890 kernel/rcu/tree.c:3251
 destroy_inode fs/inode.c:402 [inline]
 evict+0x95b/0xb10 fs/inode.c:870
 __dentry_kill+0x1a2/0x5e0 fs/dcache.c:670
 finish_dput+0xc9/0x480 fs/dcache.c:879
 __fput+0x691/0xa70 fs/file_table.c:477
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
 exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
 do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888047cb0b80
 which belongs to the cache sock_inode_cache of size 1344
The buggy address is located 128 bytes inside of
 freed 1344-byte region [ffff888047cb0b80, ffff888047cb10c0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x47cb0
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff888038584a01
flags: 0x4fff00000000040(head|node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000040 ffff888030419c80 dead000000000100 dead000000000122
raw: 0000000000000000 00000008000b000b 00000000f5000000 ffff888038584a01
head: 04fff00000000040 ffff888030419c80 dead000000000100 dead000000000122
head: 0000000000000000 00000008000b000b 00000000f5000000 ffff888038584a01
head: 04fff00000000002 ffffea00011f2c01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000004
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Reclaimable, gfp_mask 0xd20d0(__GFP_RECLAIMABLE|__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5295, tgid 5295 (syz-execprog), ts 87351971632, free_ts 76295178870
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3255 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3444
 new_slab mm/slub.c:3502 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7134
 refill_sheaf mm/slub.c:2804 [inline]
 __pcs_replace_empty_main+0x2b9/0x620 mm/slub.c:4578
 alloc_from_pcs mm/slub.c:4681 [inline]
 slab_alloc_node mm/slub.c:4815 [inline]
 kmem_cache_alloc_lru_noprof+0x37c/0x640 mm/slub.c:4849
 sock_alloc_inode+0x28/0xc0 net/socket.c:322
 alloc_inode+0x6a/0x1b0 fs/inode.c:347
 new_inode_pseudo include/linux/fs.h:3003 [inline]
 sock_alloc net/socket.c:637 [inline]
 __sock_create+0x12d/0x9d0 net/socket.c:1569
 mptcp_subflow_create_socket+0xfb/0x800 net/mptcp/subflow.c:1788
 __mptcp_socket_create net/mptcp/protocol.c:110 [inline]
 __mptcp_nmpc_sk+0x155/0x790 net/mptcp/protocol.c:142
 mptcp_setsockopt_v6 net/mptcp/sockopt.c:399 [inline]
 mptcp_setsockopt+0xe4a/0x36a0 net/mptcp/sockopt.c:922
 do_sock_setsockopt+0x270/0x400 net/socket.c:2322
 __sys_setsockopt net/socket.c:2347 [inline]
 __do_sys_setsockopt net/socket.c:2353 [inline]
 __se_sys_setsockopt net/socket.c:2350 [inline]
 __x64_sys_setsockopt+0x18a/0x210 net/socket.c:2350
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
page last free pid 5281 tgid 5281 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 __slab_free+0x263/0x2b0 mm/slub.c:5532
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4501 [inline]
 slab_alloc_node mm/slub.c:4830 [inline]
 __kmalloc_cache_noprof+0x2ba/0x660 mm/slub.c:5334
 kmalloc_noprof include/linux/slab.h:962 [inline]
 tomoyo_print_header security/tomoyo/audit.c:156 [inline]
 tomoyo_init_log+0x195/0x1fb0 security/tomoyo/audit.c:255
 tomoyo_supervisor+0x353/0x1570 security/tomoyo/common.c:2232
 tomoyo_audit_env_log security/tomoyo/environ.c:37 [inline]
 tomoyo_env_perm+0x151/0x1f0 security/tomoyo/environ.c:64
 tomoyo_environ security/tomoyo/domain.c:673 [inline]
 tomoyo_find_next_domain+0x15cb/0x1aa0 security/tomoyo/domain.c:889
 tomoyo_bprm_check_security+0x11b/0x180 security/tomoyo/tomoyo.c:102
 security_bprm_check+0x85/0x240 security/security.c:794
 search_binary_handler fs/exec.c:1654 [inline]
 exec_binprm fs/exec.c:1696 [inline]
 bprm_execve+0x896/0x1460 fs/exec.c:1748
 do_execveat_common+0x50d/0x690 fs/exec.c:1846
 __do_sys_execve fs/exec.c:1930 [inline]
 __se_sys_execve fs/exec.c:1924 [inline]
 __x64_sys_execve+0x97/0xc0 fs/exec.c:1924
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94

Memory state around the buggy address:
 ffff888047cb0b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888047cb0b80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888047cb0c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888047cb0c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888047cb0d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

---
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