syzbot

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BUG: KASAN: slab-use-after-free in reverse_path_check_proc+0x5b/0x240 fs/eventpoll.c:1663
Read of size 8 at addr ffff88803777f7e0 by task syz.3.20/6001


CPU: 0 UID: 0 PID: 6001 Comm: syz.3.20 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 reverse_path_check_proc+0x5b/0x240 fs/eventpoll.c:1663
 reverse_path_check fs/eventpoll.c:1692 [inline]
 ep_insert+0xc6c/0x1820 fs/eventpoll.c:1881
 do_epoll_ctl_file+0x8bb/0xed0 fs/eventpoll.c:2651
 do_epoll_ctl fs/eventpoll.c:2698 [inline]
 __do_sys_epoll_ctl fs/eventpoll.c:2715 [inline]
 __se_sys_epoll_ctl+0x14e/0x210 fs/eventpoll.c:2706
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f96281fce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f962783d028 EFLAGS: 00000246 ORIG_RAX: 00000000000000e9
RAX: ffffffffffffffda RBX: 00007f9628476090 RCX: 00007f96281fce59
RDX: 0000000000000003 RSI: 0000000000000001 RDI: 0000000000000006
RBP: 00007f9628292d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000200000000600 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9628476128 R14: 00007f9628476090 R15: 00007ffcab0f8478
 </TASK>

Allocated by task 5997:
 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:4583 [inline]
 slab_alloc_node mm/slub.c:4912 [inline]
 kmem_cache_alloc_noprof+0x33b/0x680 mm/slub.c:4919
 ep_attach_file fs/eventpoll.c:1751 [inline]
 ep_register_epitem fs/eventpoll.c:1833 [inline]
 ep_insert+0x512/0x1820 fs/eventpoll.c:1876
 do_epoll_ctl_file+0x8bb/0xed0 fs/eventpoll.c:2651
 do_epoll_ctl fs/eventpoll.c:2698 [inline]
 __do_sys_epoll_ctl fs/eventpoll.c:2715 [inline]
 __se_sys_epoll_ctl+0x14e/0x210 fs/eventpoll.c:2706
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5997:
 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:2700 [inline]
 slab_free mm/slub.c:6284 [inline]
 kmem_cache_free+0x187/0x6c0 mm/slub.c:6411
 eventpoll_release_file+0xc2/0x240 fs/eventpoll.c:1386
 eventpoll_release include/linux/eventpoll.h:61 [inline]
 __fput+0x83c/0xa70 fs/file_table.c:501
 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+0xf3/0x4d0 kernel/entry/common.c:98
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
 do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88803777f7e0
 which belongs to the cache ep_head of size 16
The buggy address is located 0 bytes inside of
 freed 16-byte region [ffff88803777f7e0, ffff88803777f7f0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88803777f280 pfn:0x3777f
memcg:ffff88802b46c801
flags: 0x80000000000200(workingset|node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000200 ffff888140ae73c0 ffffea0000e3c510 ffffea0000d70e90
raw: ffff88803777f280 0000000800800024 00000000f5000000 ffff88802b46c801
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 4987, tgid 4987 (udevd), ts 71313648267, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1873
 prep_new_page mm/page_alloc.c:1881 [inline]
 get_page_from_freelist+0x27d6/0x2850 mm/page_alloc.c:3954
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5297
 alloc_slab_page mm/slub.c:3289 [inline]
 allocate_slab+0x74/0x5e0 mm/slub.c:3404
 new_slab mm/slub.c:3447 [inline]
 refill_objects+0x33c/0x3d0 mm/slub.c:7226
 refill_sheaf mm/slub.c:2827 [inline]
 __pcs_replace_empty_main+0x373/0x720 mm/slub.c:4665
 alloc_from_pcs mm/slub.c:4763 [inline]
 slab_alloc_node mm/slub.c:4897 [inline]
 kmem_cache_alloc_noprof+0x433/0x680 mm/slub.c:4919
 ep_attach_file fs/eventpoll.c:1751 [inline]
 ep_register_epitem fs/eventpoll.c:1833 [inline]
 ep_insert+0x512/0x1820 fs/eventpoll.c:1876
 do_epoll_ctl_file+0x8bb/0xed0 fs/eventpoll.c:2651
 do_epoll_ctl fs/eventpoll.c:2698 [inline]
 __do_sys_epoll_ctl fs/eventpoll.c:2715 [inline]
 __se_sys_epoll_ctl+0x14e/0x210 fs/eventpoll.c:2706
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88803777f680: fa fb fc fc fa fb fc fc fa fb fc fc 00 00 fc fc
 ffff88803777f700: 00 00 fc fc 00 00 fc fc 00 00 fc fc 00 00 fc fc
>ffff88803777f780: 00 00 fc fc fa fb fc fc 00 00 fc fc fa fb fc fc
                                                       ^
 ffff88803777f800: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
 ffff88803777f880: fa fb fc fc fa fb fc fc fa fb fc fc fa fb fc fc
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