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

Status: upstream: reported C repro on 2025/04/05 13:22
Bug presence: origin:lts
[Documentation on labels]
Reported-by: syzbot+73836c72f168b93b604e@syzkaller.appspotmail.com
First crash: 315d, last: 1d06h
Fix bisection: failed (error log, bisect log)
  
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/07/13 lts (merge base) 58485ff1a74f C [report] KASAN: use-after-free Read in __ext4_check_dir_entry
2025/07/13 upstream (ToT) 3cd752194e2e 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 11 9d03h 391d 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 343d 496d 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 1970d 2074d 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 631d 641d 0/29 closed as dup on 2024/06/26 08:39
android-5-15 KASAN: use-after-free Read in __ext4_check_dir_entry (2) origin:lts 19 C 8 6d16h 311d 0/2 upstream: reported C repro on 2025/04/09 15:24
linux-5.15 KASAN: use-after-free Read in __ext4_check_dir_entry origin:upstream 19 C error 10 44d 622d 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 472d 596d 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 2874d 2877d 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 527d 645d 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 520d 644d 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 585d 622d 0/3 auto-obsoleted due to no activity on 2024/09/17 20:54
upstream KASAN: slab-use-after-free Read in __ext4_check_dir_entry ext4 19 C error 5 14d 229d 0/29 upstream: reported C repro on 2025/06/30 17:28
▶ ▼ Last patch testing requests (2)
Created Duration User Patch Repo Result
2025/07/10 23:43 15m retest repro android14-6.1 OK log
2025/06/26 02:49 9m retest repro android14-6.1 report log
▶ ▼ Fix bisection attempts (7)
Created Duration User Patch Repo Result
2026/01/21 13:31 0m bisect fix android14-6.1 error job log
2025/12/19 15:23 1h21m bisect fix android14-6.1 OK (0) job log log
2025/11/16 00:11 1h27m bisect fix android14-6.1 OK (0) job log log
2025/10/11 07:24 1h59m bisect fix android14-6.1 OK (0) job log log
2025/09/01 23:55 1h10m bisect fix android14-6.1 OK (0) job log log
2025/07/27 20:45 2h40m bisect fix android14-6.1 OK (0) job log log
2025/05/22 05:34 1h21m bisect fix android14-6.1 OK (0) job log log

Sample crash report:
EXT4-fs warning (device loop2): dx_probe:833: inode #2: comm syz.2.17: Unrecognised inode hash code 20
EXT4-fs warning (device loop2): dx_probe:966: inode #2: comm syz.2.17: 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 ffff888114763003 by task syz.2.17/378

CPU: 1 PID: 378 Comm: syz.2.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x24 lib/dump_stack.c:88
 dump_stack_lvl+0x110/0x170 lib/dump_stack.c:106
 print_address_description+0x71/0x200 mm/kasan/report.c:316
 print_report+0x4a/0x60 mm/kasan/report.c:420
 kasan_report+0x122/0x150 mm/kasan/report.c:524
 __asan_report_load2_noabort+0x14/0x20 mm/kasan/report_generic.c:349
 __ext4_check_dir_entry+0x7c2/0x970 fs/ext4/dir.c:85
 ext4_readdir+0x1315/0x3e10 fs/ext4/dir.c:261
 iterate_dir+0x271/0x610 fs/readdir.c:-1
 __do_sys_getdents64 fs/readdir.c:369 [inline]
 __se_sys_getdents64+0xf2/0x250 fs/readdir.c:354
 __x64_sys_getdents64+0x7b/0x90 fs/readdir.c:354
 x64_sys_call+0x15c/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:218
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fda30b9bf79
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:00007fda319b3028 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 00007fda30e15fa0 RCX: 00007fda30b9bf79
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000006
RBP: 00007fda30c327e0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fda30e16038 R14: 00007fda30e15fa0 R15: 00007ffd6fd34ca8
 </TASK>

Allocated by task 111:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_alloc_info+0x25/0x30 mm/kasan/generic.c:505
 ____kasan_kmalloc mm/kasan/common.c:380 [inline]
 __kasan_kmalloc+0x95/0xb0 mm/kasan/common.c:389
 kasan_kmalloc include/linux/kasan.h:212 [inline]
 kmalloc_trace+0x40/0xb0 mm/slab_common.c:1033
 kmalloc include/linux/slab.h:563 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 kernfs_fop_open+0x371/0xb80 fs/kernfs/file.c:690
 do_dentry_open+0x88e/0x1260 fs/open.c:884
 vfs_open+0x73/0x80 fs/open.c:1017
 do_open fs/namei.c:3633 [inline]
 path_openat+0x2700/0x2f80 fs/namei.c:3790
 do_filp_open+0x1f1/0x430 fs/namei.c:3817
 do_sys_openat2+0x15e/0x810 fs/open.c:1343
 do_sys_open fs/open.c:1359 [inline]
 __do_sys_openat fs/open.c:1375 [inline]
 __se_sys_openat fs/open.c:1370 [inline]
 __x64_sys_openat+0x136/0x160 fs/open.c:1370
 x64_sys_call+0x783/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:258
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff888114763000
 which belongs to the cache kmalloc-192 of size 192
The buggy address is located 3 bytes inside of
 192-byte region [ffff888114763000, ffff8881147630c0)

The buggy address belongs to the physical page:
page:ffffea000451d8c0 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888114763900 pfn:0x114763
flags: 0x4000000000000200(slab|zone=1)
raw: 4000000000000200 ffffea000451d708 ffffea000451dac8 ffff888100042c00
raw: ffff888114763900 0000000000100000 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 111, tgid 111 (udevadm), ts 4774489194, free_ts 0
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2643
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2650
 get_page_from_freelist+0x2d12/0x2d80 mm/page_alloc.c:4554
 __alloc_pages+0x1d9/0x480 mm/page_alloc.c:5868
 alloc_slab_page+0x6e/0xf0 include/linux/gfp.h:-1
 allocate_slab mm/slub.c:1967 [inline]
 new_slab+0x98/0x3d0 mm/slub.c:2020
 ___slab_alloc+0x6bd/0xb20 mm/slub.c:3177
 __slab_alloc+0x5e/0xa0 mm/slub.c:3263
 slab_alloc_node mm/slub.c:3348 [inline]
 __kmem_cache_alloc_node+0x203/0x2c0 mm/slub.c:3423
 kmalloc_trace+0x29/0xb0 mm/slab_common.c:1028
 kmalloc include/linux/slab.h:563 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 kernfs_fop_open+0x371/0xb80 fs/kernfs/file.c:690
 do_dentry_open+0x88e/0x1260 fs/open.c:884
 vfs_open+0x73/0x80 fs/open.c:1017
 do_open fs/namei.c:3633 [inline]
 path_openat+0x2700/0x2f80 fs/namei.c:3790
 do_filp_open+0x1f1/0x430 fs/namei.c:3817
 do_sys_openat2+0x15e/0x810 fs/open.c:1343
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888114762f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888114762f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888114763000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888114763080: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888114763100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
EXT4-fs error (device loop2): ext4_readdir:263: inode #2: block 3: comm syz.2.17: path /0/file0: bad entry in directory: directory entry overrun - offset=2047, inode=1942470656, rec_len=33044, size=2048 fake=0
EXT4-fs error (device loop2) in ext4_reserve_inode_write:5930: Corrupt filesystem
EXT4-fs error (device loop2): ext4_dirty_inode:6134: inode #2: comm syz.2.17: mark_inode_dirty error

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/14 00:09 android14-6.1 edbe3e111301 1e62d198 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro #1 (clean fs)] [mounted in repro #2 (corrupt fs)] ci2-android-6-1 KASAN: use-after-free Read in __ext4_check_dir_entry
2026/02/03 07:47 android14-6.1 0ddae4186735 d78927dd .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci2-android-6-1 KASAN: use-after-free Read in __ext4_check_dir_entry
2026/01/25 02:52 android14-6.1 f282db65d7e9 40acda8a .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-6-1 KASAN: use-after-free Read in __ext4_check_dir_entry
2025/06/11 08:09 android14-6.1 47e5d7e91778 5d7e17ca .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci2-android-6-1 KASAN: use-after-free Read in __ext4_check_dir_entry
2025/04/05 14:25 android14-6.1 ca24c52e3c25 c53ea9c9 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-6-1 KASAN: use-after-free Read in __ext4_check_dir_entry
2025/04/05 13:22 android14-6.1 ca24c52e3c25 c53ea9c9 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-android-6-1 KASAN: use-after-free Read in __ext4_check_dir_entry
* Struck through repros no longer work on HEAD.