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KASAN: use-after-free Read in __ext4_check_dir_entry (2)

Status: upstream: reported C repro on 2025/04/09 15:24
Bug presence: origin:lts
[Documentation on labels]
Reported-by: syzbot+89297222eb000a6d3be5@syzkaller.appspotmail.com
First crash: 102d, last: 4d22h
Bug presence (2)
Date Name Commit Repro Result
2025/04/10 lts (merge base) cf30300a216a C [report] KASAN: use-after-free Read in __ext4_check_dir_entry
2025/04/24 upstream (ToT) a79be02bba5c C Didn't crash
Similar bugs (12)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-10 KASAN: use-after-free Read in __ext4_check_dir_entry (2) 19 C 5 24d 182d 0/2 upstream: reported C repro on 2025/01/19 16:52
upstream KASAN: use-after-free Read in __ext4_check_dir_entry (3) ext4 19 C inconclusive done 6 134d 287d 0/29 auto-obsoleted due to no activity on 2025/06/16 07:57
linux-4.14 KASAN: use-after-free Read in __ext4_check_dir_entry 19 C inconclusive 6 1761d 1864d 0/1 upstream: reported C repro on 2020/06/12 02:23
upstream KASAN: use-after-free Read in __ext4_check_dir_entry (2) ext4 19 C error 1 422d 432d 0/29 closed as dup on 2024/06/26 08:39
linux-5.15 KASAN: use-after-free Read in __ext4_check_dir_entry origin:upstream 19 C error 10 49d 412d 0/3 upstream: reported C repro on 2024/06/03 01:15
android-5-15 KASAN: use-after-free Read in __ext4_check_dir_entry missing-backport origin:upstream 19 C error 4 263d 387d 0/2 auto-obsoleted due to no activity on 2025/02/07 07:57
upstream KASAN: use-after-free Read in __ext4_check_dir_entry ext4 19 C 8 2665d 2668d 22/29 closed as dup on 2018/03/31 22:38
android-5-10 KASAN: use-after-free Read in __ext4_check_dir_entry 19 C error 2 318d 436d 0/2 auto-obsoleted due to no activity on 2024/12/26 18:56
android-6-1 KASAN: use-after-free Read in __ext4_check_dir_entry missing-backport origin:upstream 19 C error 4 311d 435d 0/2 auto-obsoleted due to no activity on 2024/12/21 14:06
linux-6.1 KASAN: use-after-free Read in __ext4_check_dir_entry 19 15 376d 412d 0/3 auto-obsoleted due to no activity on 2024/09/17 20:54
android-6-1 KASAN: use-after-free Read in __ext4_check_dir_entry (2) origin:lts 19 C 3 24d 106d 0/2 upstream: reported C repro on 2025/04/05 13:22
upstream KASAN: slab-use-after-free Read in __ext4_check_dir_entry ext4 19 syz error 1 6d16h 20d 0/29 upstream: reported syz repro on 2025/06/30 17:28
Last patch testing requests (4)
Created Duration User Patch Repo Result
2025/07/04 19:35 6m retest repro android13-5.15-lts report log
2025/07/04 19:35 6m retest repro android13-5.15-lts report log
2025/04/23 19:47 8m retest repro android13-5.15-lts report log
2025/04/23 19:47 7m retest repro android13-5.15-lts report log
Fix bisection attempts (1)
Created Duration User Patch Repo Result
2025/05/27 07:11 1h38m bisect fix android13-5.15-lts OK (0) job log log

Sample crash report:
EXT4-fs warning (device loop0): dx_probe:966: inode #2: comm syz-executor749: Corrupt directory, running e2fsck is recommended
==================================================================
BUG: KASAN: use-after-free in __ext4_check_dir_entry+0x7c2/0x970 fs/ext4/dir.c:85
Read of size 2 at addr ffff88812450e003 by task syz-executor749/290

CPU: 1 PID: 290 Comm: syz-executor749 Not tainted 5.15.188-syzkaller-00606-g6b619c45dff5 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:88
 dump_stack_lvl+0xee/0x150 lib/dump_stack.c:106
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:427 [inline]
 kasan_report+0xf1/0x140 mm/kasan/report.c:444
 __asan_report_load2_noabort+0x14/0x20 mm/kasan/report_generic.c:307
 __ext4_check_dir_entry+0x7c2/0x970 fs/ext4/dir.c:85
 ext4_readdir+0x11c9/0x3a40 fs/ext4/dir.c:261
 iterate_dir+0x260/0x600 fs/readdir.c:-1
 __do_sys_getdents64 fs/readdir.c:369 [inline]
 __se_sys_getdents64+0xe5/0x240 fs/readdir.c:354
 __x64_sys_getdents64+0x7b/0x90 fs/readdir.c:354
 x64_sys_call+0x592/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:218
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fe494f634a9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 21 18 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe3cae8448 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007fe494fac650 RCX: 00007fe494f634a9
RDX: 0000000000000010 RSI: 0000000000000000 RDI: 0000000000000006
RBP: 0000200000000000 R08: 00007ffe3cae8480 R09: 00007ffe3cae8480
R10: 00007ffe3cae8480 R11: 0000000000000246 R12: 0000000000000001
R13: 0000000000000000 R14: 431bde82d7b634db R15: 00007ffe3cae84a0
 </TASK>

The buggy address belongs to the page:
page:ffffea0004914380 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x12450e
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 ffffea00049143c8 ffffea0004914308 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 0x100cca(GFP_HIGHUSER_MOVABLE), pid 285, ts 22260001475, free_ts 22260352619
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x192/0x1b0 mm/page_alloc.c:2605
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2611
 get_page_from_freelist+0x2cc5/0x2d50 mm/page_alloc.c:4485
 __alloc_pages+0x18f/0x440 mm/page_alloc.c:5795
 __alloc_pages_node include/linux/gfp.h:591 [inline]
 alloc_pages_node include/linux/gfp.h:605 [inline]
 alloc_pages include/linux/gfp.h:618 [inline]
 wp_page_copy+0x20f/0x18f0 mm/memory.c:3226
 do_wp_page+0x731/0xc90 mm/memory.c:-1
 handle_pte_fault+0x73c/0x2680 mm/memory.c:4932
 __handle_mm_fault mm/memory.c:-1 [inline]
 do_handle_mm_fault+0x1a6d/0x1d50 mm/memory.c:5333
 handle_mm_fault include/linux/mm.h:1836 [inline]
 do_user_addr_fault+0x841/0x1180 arch/x86/mm/fault.c:1418
 handle_page_fault arch/x86/mm/fault.c:1509 [inline]
 exc_page_fault+0x51/0xb0 arch/x86/mm/fault.c:1565
 asm_exc_page_fault+0x27/0x30 arch/x86/include/asm/idtentry.h:606
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1472 [inline]
 free_pcp_prepare mm/page_alloc.c:1544 [inline]
 free_unref_page_prepare+0x542/0x550 mm/page_alloc.c:3534
 free_unref_page_list+0x134/0x9d0 mm/page_alloc.c:3671
 release_pages+0xfda/0x1030 mm/swap.c:1014
 free_pages_and_swap_cache+0x86/0xa0 mm/swap_state.c:320
 tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:240 [inline]
 tlb_flush_mmu mm/mmu_gather.c:247 [inline]
 tlb_finish_mmu+0x175/0x300 mm/mmu_gather.c:338
 unmap_region+0x315/0x360 mm/mmap.c:2688
 __do_munmap+0xa0e/0xfe0 mm/mmap.c:2921
 __vm_munmap+0x15b/0x2a0 mm/mmap.c:2974
 __do_sys_munmap mm/mmap.c:3000 [inline]
 __se_sys_munmap mm/mmap.c:2996 [inline]
 __x64_sys_munmap+0x6b/0x80 mm/mmap.c:2996
 x64_sys_call+0xc9/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:12
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Memory state around the buggy address:
 ffff88812450df00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88812450df80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88812450e000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff88812450e080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812450e100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs error (device loop0): ext4_readdir:263: inode #2: block 255: comm syz-executor749: path (unknown): bad entry in directory: rec_len is smaller than minimal - offset=1023, inode=0, rec_len=0, size=1024 fake=0

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/07/16 01:21 android13-5.15-lts 6b619c45dff5 03fcfc4b .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 KASAN: use-after-free Read in __ext4_check_dir_entry
2025/07/15 09:14 android13-5.15-lts eabc268e4fb2 03fcfc4b .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 KASAN: use-after-free Read in __ext4_check_dir_entry
2025/06/19 11:37 android13-5.15-lts e678c93d43cc ed3e87f7 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci2-android-5-15 KASAN: use-after-free Read in __ext4_check_dir_entry
2025/04/09 16:51 android13-5.15-lts 760764029c6d 47d015b1 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 KASAN: use-after-free Read in __ext4_check_dir_entry
2025/04/09 15:23 android13-5.15-lts 760764029c6d 47d015b1 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-5-15 KASAN: use-after-free Read in __ext4_check_dir_entry
* Struck through repros no longer work on HEAD.