KASAN: use-after-free Read in ext4_search_dir

Status: upstream: reported C repro on 2023/06/18 19:29
Bug presence: origin:upstream
Labels: missing-backport
[Documentation on labels]
Reported-by: syzbot+2003a2bf24a18682dbf1@syzkaller.appspotmail.com
First crash: 1160d, last: 699d
Fix commit to backport (bisect log) :
tree: upstream
commit c6b72f5d82b1017bad80f9ebf502832fc321d796
Author: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Date: Wed Aug 21 15:23:24 2024 +0000

  ext4: avoid OOB when system.data xattr changes underneath the filesystem

  
Fix bisection: the issue occurs on the latest tested release (bisect log)
Crash: KASAN: use-after-free Read in ext4_search_dir (log)
Repro: C syz .config
  
▶ ▼ Bug presence (3)
Date Name Commit Repro Result
2024/09/21 linux-6.1.y (ToT) e526b12bf916 C [report] KASAN: use-after-free Read in ext4_search_dir
2023/06/19 upstream (ToT) 45a3e24f65e9 C [report] KASAN: use-after-free Read in ext4_search_dir
2024/09/21 upstream (ToT) 88264981f208 C Didn't crash
▶ ▼ Similar bugs (10)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: use-after-free Read in ext4_search_dir (3) prio:high actionable ext4 19 2 19d 44d 0/29 upstream: reported on 2026/07/09 00:07
android-5-15 KASAN: slab-out-of-bounds Read in ext4_search_dir origin:upstream missing-backport 19 syz, C done 6 649d 1008d 0/2 auto-obsoleted due to no activity on 2025/02/18 18:03
linux-5.15 KASAN: use-after-free Read in ext4_search_dir 19 syz, C done 5 684d 1162d 3/3 fixed on 2024/11/08 17:20
android-54 KASAN: use-after-free Read in ext4_search_dir 19 syz, C 17 689d 858d 0/2 auto-obsoleted due to no activity on 2025/02/18 14:16
upstream KASAN: use-after-free Read in ext4_search_dir prio:low ext4 19 syz, C error done 20 957d 1198d 25/29 fixed on 2024/02/21 18:23
upstream KASAN: slab-out-of-bounds Read in ext4_search_dir ext4 19 syz, C 5 240d 324d 29/29 fixed on 2026/05/06 16:40
android-6-1 KASAN: use-after-free Read in ext4_search_dir missing-backport origin:upstream 19 syz, C error error 32 21d 1034d 0/2 upstream: reported C repro on 2023/10/22 16:55
android-5-15 KASAN: use-after-free Read in ext4_search_dir origin:upstream 19 syz, C 4 31d 61d 0/2 upstream: reported C repro on 2026/06/21 07:51
android-5-10 KASAN: slab-out-of-bounds Read in ext4_search_dir 19 syz, C error 24 61d 1008d 0/2 upstream: reported C repro on 2023/11/17 09:38
upstream KASAN: use-after-free Read in ext4_search_dir (2) ext4 19 syz, C 5 709d 732d 28/29 fixed on 2024/10/22 11:57
▶ ▼ Fix bisection attempts (13)
Created Duration User Patch Repo Result
2024/09/30 03:35 5h53m fix candidate upstream OK (1) job log
2024/09/12 02:43 1h22m bisect fix linux-6.1.y OK (0) job log log
2024/08/08 08:54 1h07m bisect fix linux-6.1.y OK (0) job log log
2024/06/29 10:39 1h46m bisect fix linux-6.1.y OK (0) job log log
2024/05/21 15:56 1h00m bisect fix linux-6.1.y OK (0) job log log
2024/04/17 17:39 2h20m bisect fix linux-6.1.y OK (0) job log log
2024/03/14 18:12 1h51m bisect fix linux-6.1.y OK (0) job log log
2024/02/09 03:10 1h24m bisect fix linux-6.1.y OK (0) job log log
2024/01/02 00:37 1h07m bisect fix linux-6.1.y OK (0) job log log
2023/12/02 00:57 1h01m bisect fix linux-6.1.y OK (0) job log log
2023/11/01 09:38 1h22m bisect fix linux-6.1.y OK (0) job log log
2023/10/01 10:48 1h02m bisect fix linux-6.1.y OK (0) job log log
2023/08/03 01:46 3h10m bisect fix linux-6.1.y OK (0) job log log

Sample crash report:
EXT4-fs: Ignoring removed bh option
EXT4-fs (loop0): mounting ext3 file system using the ext4 subsystem
EXT4-fs (loop0): 1 truncate cleaned up
EXT4-fs (loop0): mounted filesystem without journal. Quota mode: none.
==================================================================
BUG: KASAN: use-after-free in ext4_search_dir+0xee/0x1b0 fs/ext4/namei.c:1539
Read of size 1 at addr ffff8880707743ed by task syz-executor361/3543

CPU: 0 PID: 3543 Comm: syz-executor361 Not tainted 6.1.34-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/27/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:284 [inline]
 print_report+0x15f/0x4f0 mm/kasan/report.c:395
 kasan_report+0x136/0x160 mm/kasan/report.c:495
 ext4_search_dir+0xee/0x1b0 fs/ext4/namei.c:1539
 ext4_find_inline_entry+0x4b6/0x5e0 fs/ext4/inline.c:1722
 __ext4_find_entry+0x2b0/0x1b20 fs/ext4/namei.c:1612
 ext4_lookup_entry fs/ext4/namei.c:1767 [inline]
 ext4_lookup+0x176/0x740 fs/ext4/namei.c:1835
 lookup_open fs/namei.c:3391 [inline]
 open_last_lookups fs/namei.c:3481 [inline]
 path_openat+0x10fb/0x2e60 fs/namei.c:3711
 do_filp_open+0x230/0x480 fs/namei.c:3741
 do_sys_openat2+0x13b/0x500 fs/open.c:1318
 do_sys_open fs/open.c:1334 [inline]
 __do_sys_open fs/open.c:1342 [inline]
 __se_sys_open fs/open.c:1338 [inline]
 __x64_sys_open+0x221/0x270 fs/open.c:1338
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f32c086f2d9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 14 00 00 90 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff59504138 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007fff59504178 RCX: 00007f32c086f2d9
RDX: 0000000000000000 RSI: 0000000000141042 RDI: 0000000020000100
RBP: 0000000000000000 R08: 000000000001f210 R09: 0000000000000000
R10: 00007f32b0061000 R11: 0000000000000246 R12: 00007fff59504170
R13: 0000000000000000 R14: 431bde82d7b634db R15: 0000000000000000
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0001c1dd00 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x70774
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea0001c1dd48 ffffea0001c1dc88 0000000000000000
raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Movable, gfp_mask 0x140dca(GFP_HIGHUSER_MOVABLE|__GFP_COMP|__GFP_ZERO), pid 3543, tgid 3543 (syz-executor361), ts 66021111866, free_ts 66049240361
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x18d/0x1b0 mm/page_alloc.c:2533
 prep_new_page mm/page_alloc.c:2540 [inline]
 get_page_from_freelist+0x32ed/0x3480 mm/page_alloc.c:4292
 __alloc_pages+0x28d/0x770 mm/page_alloc.c:5559
 __folio_alloc+0xf/0x30 mm/page_alloc.c:5591
 vma_alloc_folio+0x486/0x990 mm/mempolicy.c:2241
 alloc_page_vma include/linux/gfp.h:284 [inline]
 do_anonymous_page mm/memory.c:4123 [inline]
 handle_pte_fault mm/memory.c:4962 [inline]
 __handle_mm_fault mm/memory.c:5106 [inline]
 handle_mm_fault+0x2e85/0x5330 mm/memory.c:5227
 do_user_addr_fault arch/x86/mm/fault.c:1428 [inline]
 handle_page_fault arch/x86/mm/fault.c:1519 [inline]
 exc_page_fault+0x58d/0x790 arch/x86/mm/fault.c:1575
 asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:570
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1460 [inline]
 free_pcp_prepare mm/page_alloc.c:1510 [inline]
 free_unref_page_prepare+0xf63/0x1120 mm/page_alloc.c:3388
 free_unref_page_list+0x107/0x810 mm/page_alloc.c:3530
 release_pages+0x2836/0x2b40 mm/swap.c:1055
 tlb_batch_pages_flush mm/mmu_gather.c:59 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:254 [inline]
 tlb_flush_mmu+0xfc/0x210 mm/mmu_gather.c:261
 tlb_finish_mmu+0xce/0x1f0 mm/mmu_gather.c:361
 unmap_region+0x29f/0x2f0 mm/mmap.c:2229
 do_mas_align_munmap+0xe98/0x15e0 mm/mmap.c:2482
 do_mas_munmap+0x246/0x2b0 mm/mmap.c:2540
 __vm_munmap+0x268/0x370 mm/mmap.c:2817
 __do_sys_munmap mm/mmap.c:2842 [inline]
 __se_sys_munmap mm/mmap.c:2839 [inline]
 __x64_sys_munmap+0x5c/0x70 mm/mmap.c:2839
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Memory state around the buggy address:
 ffff888070774280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888070774300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888070774380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                          ^
 ffff888070774400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888070774480: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2023/06/18 19:28 linux-6.1.y ca87e77a2ef8 f3921d4d .config console log report syz C [disk image] [vmlinux] [kernel image] [mounted in repro #1] [mounted in repro #2] ci2-linux-6-1-kasan KASAN: use-after-free Read in ext4_search_dir
* Struck through repros no longer work on HEAD.