KASAN: slab-use-after-free Read in current_time

Status: fixed on 2026/07/15 08:27
Subsystems: kernfs
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+36e50496c8ac4bcde3f9@syzkaller.appspotmail.com
Fix commit: b93c55b4932d bpf: fix UAF by restoring RCU-delayed inode freeing in bpffs
First crash: 56d, last: 56d
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
781c235e-7f80-4ef4-a55b-417c07044eed assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-use-after-free Read in current_time 2026/05/29 23:51 2026/05/29 23:51 2026/05/30 00:38 6b4a844333e83556da95d61d7f207e7ef5cd4bc6 

			
				
	

	
	



			

		

	

	
	

		

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			Discussions (3)
		

		

			
			
			



	
	

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			[PATCH v2] bpf: fix UAF by restoring RCU-delayed inode freeing in bpffs
			4 (4)
			2026/06/02 04:10
		

	
		

			[PATCH] fs/namei: fix UAF in pick_link() by unlazying before atime check
			3 (3)
			2026/06/02 01:40
		

	
		

			[syzbot] [fs?] KASAN: slab-use-after-free Read in current_time
			0 (3)
			2026/06/02 01:39
		

	
	




			
			
		

	

	
	

		

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			Similar bugs (2)
		

		

			




	
	

		
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			upstream
			
				BUG: unable to handle kernel paging request in current_time
					hfs
			
			8
			C
			
			
			5
			1302d
			
				
					1319d
				
			
			
			
			
				0/29
			
			
				
					
						auto-obsoleted due to no activity on 2023/04/28 03:51
					
				
			
			
		

	
		

			android-6-1
			
				KASAN: use-after-free Read in current_time
			
			19
			C
			
			
			1
			23h52m
			
				
					23h51m
				
			
			
			
			
				0/2
			
			
				
					
						upstream: reported C repro on 2026/07/22 21:48
					
				
			
			
		

	
	





			
			
			
			
		

	

	
	

		

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			Last patch testing requests (2)
		

		

			
			

	

		
		
		

			
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				2026/06/02 01:39
				
					28m
				
				
					
						kartikey406@gmail.com
					
				
				patch
				upstream
				
				
					
						OK
						
					
					
					
						log
					
					
					
				
			

		
			

				
				2026/06/01 23:48
				
					27m
				
				
					
						kartikey406@gmail.com
					
				
				patch
				upstream
				
				
					
						OK
						
					
					
					
						log
					
					
					
				
			

		
		
	



			
			
			
		

	

	

	
	
Sample crash report:

	
==================================================================
BUG: KASAN: slab-use-after-free in is_mgtime include/linux/fs.h:2313 [inline]
BUG: KASAN: slab-use-after-free in current_time+0x354/0x3b0 fs/inode.c:2378
Read of size 2 at addr ffff8880407e4282 by task syz.0.661/9127

CPU: 3 UID: 0 PID: 9127 Comm: syz.0.661 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
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1d0 mm/kasan/report.c:595
 is_mgtime include/linux/fs.h:2313 [inline]
 current_time+0x354/0x3b0 fs/inode.c:2378
 atime_needs_update+0x33f/0x6b0 fs/inode.c:2236
 pick_link+0x3b0/0x13c0 fs/namei.c:2040
 step_into_slowpath+0x9ba/0xf90 fs/namei.c:2123
 step_into fs/namei.c:2148 [inline]
 walk_component fs/namei.c:2284 [inline]
 link_path_walk+0xf28/0x1cc0 fs/namei.c:2652
 path_parentat fs/namei.c:2856 [inline]
 __filename_parentat+0x213/0x740 fs/namei.c:2880
 filename_parentat fs/namei.c:2898 [inline]
 filename_unlinkat+0xf7/0x730 fs/namei.c:5537
 __do_sys_unlinkat fs/namei.c:5597 [inline]
 __se_sys_unlinkat fs/namei.c:5589 [inline]
 __x64_sys_unlinkat+0xc0/0x130 fs/namei.c:5589
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2baad9ce59
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:00007f2babd0b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000107
RAX: ffffffffffffffda RBX: 00007f2bab015fa0 RCX: 00007f2baad9ce59
RDX: 0000000000000000 RSI: 00002000000001c0 RDI: 0000000000000004
RBP: 00007f2baae32d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2bab016038 R14: 00007f2bab015fa0 R15: 00007ffdc75513d8
 </TASK>

Allocated by task 9127:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 unpoison_slab_object mm/kasan/common.c:340 [inline]
 __kasan_slab_alloc+0x89/0x90 mm/kasan/common.c:366
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4570 [inline]
 slab_alloc_node mm/slub.c:4899 [inline]
 kmem_cache_alloc_lru_noprof+0x246/0x6e0 mm/slub.c:4918
 alloc_inode+0x183/0x250 fs/inode.c:347
 new_inode+0x22/0x1c0 fs/inode.c:1179
 bpf_get_inode kernel/bpf/inode.c:117 [inline]
 bpf_get_inode kernel/bpf/inode.c:102 [inline]
 bpf_symlink+0x69/0x240 kernel/bpf/inode.c:391
 vfs_symlink fs/namei.c:5643 [inline]
 vfs_symlink+0x178/0x4d0 fs/namei.c:5622
 filename_symlinkat+0x2a6/0x560 fs/namei.c:5668
 __do_sys_symlinkat fs/namei.c:5688 [inline]
 __se_sys_symlinkat fs/namei.c:5683 [inline]
 __x64_sys_symlinkat+0x9c/0xe0 fs/namei.c:5683
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 9128:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2689 [inline]
 slab_free mm/slub.c:6251 [inline]
 kmem_cache_free+0x127/0x6c0 mm/slub.c:6378
 destroy_inode+0xcb/0x1c0 fs/inode.c:394
 evict+0x599/0xad0 fs/inode.c:865
 iput_final fs/inode.c:1960 [inline]
 iput.part.0+0x605/0xf50 fs/inode.c:2009
 iput+0x35/0x40 fs/inode.c:1975
 filename_unlinkat+0x466/0x730 fs/namei.c:5572
 __do_sys_unlinkat fs/namei.c:5597 [inline]
 __se_sys_unlinkat fs/namei.c:5589 [inline]
 __x64_sys_unlinkat+0xc0/0x130 fs/namei.c:5589
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff8880407e4280
 which belongs to the cache inode_cache of size 1088
The buggy address is located 2 bytes inside of
 freed 1088-byte region [ffff8880407e4280, ffff8880407e46c0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x407e0
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff8880407e7b81
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801d6bc000 dead000000000100 dead000000000122
raw: 0000000000000000 00000008001a001a 00000000f5000000 ffff8880407e7b81
head: 00fff00000000040 ffff88801d6bc000 dead000000000100 dead000000000122
head: 0000000000000000 00000008001a001a 00000000f5000000 ffff8880407e7b81
head: 00fff00000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Reclaimable, gfp_mask 0xd20d0(__GFP_RECLAIMABLE|__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5773, tgid 5773 (syz-executor), ts 108002716269, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1853
 prep_new_page mm/page_alloc.c:1861 [inline]
 get_page_from_freelist+0x11a6/0x3410 mm/page_alloc.c:3941
 __alloc_frozen_pages_noprof+0x27c/0x2bc0 mm/page_alloc.c:5221
 alloc_slab_page mm/slub.c:3278 [inline]
 allocate_slab mm/slub.c:3467 [inline]
 new_slab+0xa6/0x6c0 mm/slub.c:3525
 refill_objects+0x277/0x420 mm/slub.c:7272
 refill_sheaf mm/slub.c:2816 [inline]
 __pcs_replace_empty_main+0x375/0x650 mm/slub.c:4652
 alloc_from_pcs mm/slub.c:4750 [inline]
 slab_alloc_node mm/slub.c:4884 [inline]
 kmem_cache_alloc_lru_noprof+0x485/0x6e0 mm/slub.c:4918
 alloc_inode+0x183/0x250 fs/inode.c:347
 iget_locked+0x1d9/0x6d0 fs/inode.c:1474
 kernfs_get_inode+0x46/0x470 fs/kernfs/inode.c:252
 kernfs_iop_lookup+0x1a7/0x2d0 fs/kernfs/dir.c:1274
 lookup_open.isra.0+0x631/0x11b0 fs/namei.c:4484
 open_last_lookups fs/namei.c:4611 [inline]
 path_openat+0xa98/0x31a0 fs/namei.c:4855
 do_file_open+0x20e/0x430 fs/namei.c:4887
 do_sys_openat2+0x10d/0x1e0 fs/open.c:1364
 do_sys_open fs/open.c:1370 [inline]
 __do_sys_openat fs/open.c:1386 [inline]
 __se_sys_openat fs/open.c:1381 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1381
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8880407e4180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880407e4200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880407e4280: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8880407e4300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880407e4380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================



	

	



	Crashes (2):
		
		

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			2026/05/28 19:20
			upstream
			eb3f4b7426cf
			9a5a7e5e
			.config
			console log
			report
			syz / log
			C
			
			
				[disk image (non-bootable)]
			
				[vmlinux]
			
				[kernel image]
			
			ci-qemu-upstream
			KASAN: slab-use-after-free Read in current_time
		

		
		

			2026/05/28 16:56
			upstream
			eb3f4b7426cf
			9a5a7e5e
			.config
			console log
			report
			syz / log
			C
			
			
				[disk image (non-bootable)]
			
				[vmlinux]
			
				[kernel image]
			
			ci-qemu-upstream
			KASAN: slab-use-after-free Read in current_time
		

		
		


* Struck through repros no longer work on HEAD.