syzbot


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

Status: moderation: reported on 2025/08/02 20:03
Subsystems: afs
[Documentation on labels]
Reported-by: syzbot+cf6dfe6afe9254002996@syzkaller.appspotmail.com
First crash: 23d, last: 23d
Similar bugs (1)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.14 KASAN: use-after-free Read in radix_tree_next_chunk 19 C 465 919d 2054d 0/1 upstream: reported C repro on 2020/01/06 15:45

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in node_maxindex lib/radix-tree.c:218 [inline]
BUG: KASAN: slab-use-after-free in radix_tree_next_chunk+0xad7/0xb20 lib/radix-tree.c:1231
Read of size 1 at addr ffff88804261cb00 by task syz.8.6871/31770

CPU: 1 UID: 0 PID: 31770 Comm: syz.8.6871 Not tainted 6.16.0-syzkaller-00857-gced1b9e0392d #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xcd/0x630 mm/kasan/report.c:482
 kasan_report+0xe0/0x110 mm/kasan/report.c:595
 node_maxindex lib/radix-tree.c:218 [inline]
 radix_tree_next_chunk+0xad7/0xb20 lib/radix-tree.c:1231
 idr_get_next_ul+0x227/0x2e0 lib/idr.c:236
 idr_get_next+0x9b/0x150 lib/idr.c:267
 afs_dynroot_readdir_cells fs/afs/dynroot.c:293 [inline]
 afs_dynroot_readdir+0x72b/0xb70 fs/afs/dynroot.c:352
 iterate_dir+0x293/0xb40 fs/readdir.c:108
 __do_compat_sys_getdents fs/readdir.c:579 [inline]
 __se_compat_sys_getdents fs/readdir.c:565 [inline]
 __ia32_compat_sys_getdents+0x13b/0x2b0 fs/readdir.c:565
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
 do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e
RIP: 0023:0xf7fc4579
Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00
RSP: 002b:00000000f4c8155c EFLAGS: 00000296 ORIG_RAX: 000000000000008d
RAX: ffffffffffffffda RBX: 0000000000000008 RCX: 00000000800008c0
RDX: 0000000000000036 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000296 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Allocated by task 31770:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_save_track+0x14/0x30 mm/kasan/common.c:68
 unpoison_slab_object mm/kasan/common.c:319 [inline]
 __kasan_slab_alloc+0x89/0x90 mm/kasan/common.c:345
 kasan_slab_alloc include/linux/kasan.h:250 [inline]
 slab_post_alloc_hook mm/slub.c:4148 [inline]
 slab_alloc_node mm/slub.c:4197 [inline]
 kmem_cache_alloc_noprof+0x1cb/0x3b0 mm/slub.c:4204
 radix_tree_node_alloc.constprop.0+0x7c/0x350 lib/radix-tree.c:276
 idr_get_free+0x528/0xa30 lib/radix-tree.c:1506
 idr_alloc_u32+0x190/0x2f0 lib/idr.c:46
 idr_alloc_cyclic+0x10b/0x230 lib/idr.c:125
 afs_alloc_cell fs/afs/cell.c:203 [inline]
 afs_lookup_cell+0xe68/0x1680 fs/afs/cell.c:265
 afs_dynroot_lookup_cell fs/afs/dynroot.c:111 [inline]
 afs_dynroot_lookup+0x2e2/0xa90 fs/afs/dynroot.c:159
 lookup_one_qstr_excl+0x1ce/0x250 fs/namei.c:1697
 do_renameat2+0x56d/0xc50 fs/namei.c:5230
 __do_sys_rename fs/namei.c:5325 [inline]
 __se_sys_rename fs/namei.c:5323 [inline]
 __ia32_sys_rename+0x7c/0xa0 fs/namei.c:5323
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x7c/0x3a0 arch/x86/entry/syscall_32.c:306
 do_fast_syscall_32+0x32/0x80 arch/x86/entry/syscall_32.c:331
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e

Freed by task 31754:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_save_track+0x14/0x30 mm/kasan/common.c:68
 kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:576
 poison_slab_object mm/kasan/common.c:247 [inline]
 __kasan_slab_free+0x51/0x70 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]
 kmem_cache_free+0x2d1/0x4d0 mm/slub.c:4745
 rcu_do_batch kernel/rcu/tree.c:2576 [inline]
 rcu_core+0x799/0x14e0 kernel/rcu/tree.c:2832
 handle_softirqs+0x216/0x8e0 kernel/softirq.c:579
 __do_softirq kernel/softirq.c:613 [inline]
 invoke_softirq kernel/softirq.c:453 [inline]
 __irq_exit_rcu+0x109/0x170 kernel/softirq.c:680
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
 sysvec_apic_timer_interrupt+0x57/0xc0 arch/x86/kernel/apic/apic.c:1050
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702

Last potentially related work creation:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_record_aux_stack+0xa7/0xc0 mm/kasan/generic.c:548
 __call_rcu_common.constprop.0+0xa5/0xa10 kernel/rcu/tree.c:3094
 radix_tree_node_free lib/radix-tree.c:310 [inline]
 delete_node+0x1fc/0x8d0 lib/radix-tree.c:573
 __radix_tree_delete+0x193/0x3d0 lib/radix-tree.c:1379
 radix_tree_delete_item+0xea/0x230 lib/radix-tree.c:1430
 afs_cell_destroy+0x1db/0x310 fs/afs/cell.c:523
 rcu_do_batch kernel/rcu/tree.c:2576 [inline]
 rcu_core+0x799/0x14e0 kernel/rcu/tree.c:2832
 handle_softirqs+0x216/0x8e0 kernel/softirq.c:579
 __do_softirq kernel/softirq.c:613 [inline]
 invoke_softirq kernel/softirq.c:453 [inline]
 __irq_exit_rcu+0x109/0x170 kernel/softirq.c:680
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1050
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702

The buggy address belongs to the object at ffff88804261cb00
 which belongs to the cache radix_tree_node of size 576
The buggy address is located 0 bytes inside of
 freed 576-byte region [ffff88804261cb00, ffff88804261cd40)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x4261c
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff88804ba2fc01
flags: 0x4fff00000000040(head|node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000040 ffff88801b84cb40 ffffea0001c01400 dead000000000002
raw: 0000000000000000 0000000080170017 00000000f5000000 ffff88804ba2fc01
head: 04fff00000000040 ffff88801b84cb40 ffffea0001c01400 dead000000000002
head: 0000000000000000 0000000080170017 00000000f5000000 ffff88804ba2fc01
head: 04fff00000000002 ffffea0001098701 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 0x52810(GFP_NOWAIT|__GFP_RECLAIMABLE|__GFP_NORETRY|__GFP_COMP), pid 20912, tgid 20910 (syz.7.4284), ts 714116691814, free_ts 366964682186
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1c0/0x230 mm/page_alloc.c:1704
 prep_new_page mm/page_alloc.c:1712 [inline]
 get_page_from_freelist+0x1321/0x3890 mm/page_alloc.c:3669
 __alloc_frozen_pages_noprof+0x261/0x23f0 mm/page_alloc.c:4959
 alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2419
 alloc_slab_page mm/slub.c:2451 [inline]
 allocate_slab mm/slub.c:2619 [inline]
 new_slab+0x23b/0x330 mm/slub.c:2673
 ___slab_alloc+0xd9c/0x1940 mm/slub.c:3859
 __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3949
 __slab_alloc_node mm/slub.c:4024 [inline]
 slab_alloc_node mm/slub.c:4185 [inline]
 kmem_cache_alloc_lru_noprof+0xf4/0x3b0 mm/slub.c:4216
 xas_alloc+0x34f/0x460 lib/xarray.c:378
 xas_create+0x72b/0x1460 lib/xarray.c:685
 xas_store+0x90/0x1910 lib/xarray.c:795
 shmem_add_to_page_cache+0x662/0x9a0 mm/shmem.c:910
 shmem_alloc_and_add_folio+0x668/0xc20 mm/shmem.c:1916
 shmem_get_folio_gfp+0x67f/0x1600 mm/shmem.c:2536
 shmem_fault+0x1fe/0xa30 mm/shmem.c:2737
 __do_fault+0x10d/0x490 mm/memory.c:5169
page last free pid 12921 tgid 12921 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1248 [inline]
 __free_frozen_pages+0x7fe/0x1180 mm/page_alloc.c:2706
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x4d/0x120 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x195/0x1e0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:329
 kasan_slab_alloc include/linux/kasan.h:250 [inline]
 slab_post_alloc_hook mm/slub.c:4148 [inline]
 slab_alloc_node mm/slub.c:4197 [inline]
 __do_kmalloc_node mm/slub.c:4327 [inline]
 __kmalloc_noprof+0x1d4/0x510 mm/slub.c:4340
 kmalloc_noprof include/linux/slab.h:909 [inline]
 tomoyo_realpath_from_path+0xc2/0x6e0 security/tomoyo/realpath.c:251
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path_perm+0x274/0x460 security/tomoyo/file.c:822
 security_inode_getattr+0x116/0x290 security/security.c:2377
 vfs_getattr fs/stat.c:259 [inline]
 vfs_fstat+0x4b/0xe0 fs/stat.c:281
 __do_sys_newfstat+0x87/0x100 fs/stat.c:555
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88804261ca00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88804261ca80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88804261cb00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff88804261cb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88804261cc00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
----------------
Code disassembly (best guess), 2 bytes skipped:
   0:	10 06                	adc    %al,(%rsi)
   2:	03 74 b4 01          	add    0x1(%rsp,%rsi,4),%esi
   6:	10 07                	adc    %al,(%rdi)
   8:	03 74 b0 01          	add    0x1(%rax,%rsi,4),%esi
   c:	10 08                	adc    %cl,(%rax)
   e:	03 74 d8 01          	add    0x1(%rax,%rbx,8),%esi
  1e:	00 51 52             	add    %dl,0x52(%rcx)
  21:	55                   	push   %rbp
  22:	89 e5                	mov    %esp,%ebp
  24:	0f 34                	sysenter
  26:	cd 80                	int    $0x80
* 28:	5d                   	pop    %rbp <-- trapping instruction
  29:	5a                   	pop    %rdx
  2a:	59                   	pop    %rcx
  2b:	c3                   	ret
  2c:	90                   	nop
  2d:	90                   	nop
  2e:	90                   	nop
  2f:	90                   	nop
  30:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi
  37:	8d b4 26 00 00 00 00 	lea    0x0(%rsi,%riz,1),%esi

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/07/29 19:59 upstream ced1b9e0392d ba28e0a8 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 KASAN: slab-use-after-free Read in radix_tree_next_chunk
* Struck through repros no longer work on HEAD.