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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: 10d, last: 10d
Bug presence (2)
Date Name Commit Repro Result
2025/04/06 lts (merge base) 3a8358583626 C [report] KASAN: use-after-free Read in __ext4_check_dir_entry
2025/04/06 upstream (ToT) f4d2ef48250a C Failed due to an error; will retry later
Similar bugs (11)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-10 KASAN: use-after-free Read in __ext4_check_dir_entry (2) C 5 13d 86d 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 C inconclusive done 6 39d 191d 0/28 upstream: reported C repro on 2024/10/06 17:11
linux-4.14 KASAN: use-after-free Read in __ext4_check_dir_entry C inconclusive 6 1665d 1769d 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 C error 1 326d 336d 0/28 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 C 2 6d15h 6d17h 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 C error 10 57d 317d 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 C error 4 168d 291d 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 C 8 2569d 2572d 22/28 closed as dup on 2018/03/31 22:38
android-5-10 KASAN: use-after-free Read in __ext4_check_dir_entry C error 2 222d 340d 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 C error 4 215d 339d 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 15 280d 317d 0/3 auto-obsoleted due to no activity on 2024/09/17 20:54

Sample crash report:
EXT4-fs error (device loop0): ext4_orphan_get:1405: comm syz-executor267: couldn't read orphan inode 15 (err -117)
EXT4-fs (loop0): mounted filesystem without journal. Quota mode: none.
EXT4-fs warning (device loop0): dx_probe:833: inode #2: comm syz-executor267: Unrecognised inode hash code 4
EXT4-fs warning (device loop0): dx_probe:966: inode #2: comm syz-executor267: Corrupt directory, running e2fsck is recommended
==================================================================
BUG: KASAN: use-after-free in __ext4_check_dir_entry+0x700/0x880 fs/ext4/dir.c:85
Read of size 2 at addr ffff88811e922003 by task syz-executor267/297

CPU: 0 PID: 297 Comm: syz-executor267 Not tainted 6.1.129-syzkaller-00055-gca24c52e3c25 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x151/0x1b7 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0x158/0x4e0 mm/kasan/report.c:427
 kasan_report+0x13c/0x170 mm/kasan/report.c:531
 __asan_report_load2_noabort+0x14/0x20 mm/kasan/report_generic.c:349
 __ext4_check_dir_entry+0x700/0x880 fs/ext4/dir.c:85
 ext4_readdir+0x1290/0x3860 fs/ext4/dir.c:258
 iterate_dir+0x265/0x600 fs/readdir.c:-1
 __do_sys_getdents64 fs/readdir.c:369 [inline]
 __se_sys_getdents64+0x1c1/0x460 fs/readdir.c:354
 __x64_sys_getdents64+0x7b/0x90 fs/readdir.c:354
 x64_sys_call+0x5ae/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:218
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f168cb864f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 1f 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:00007ffcb4f1b988 EFLAGS: 00000246 ORIG_RAX: 00000000000000d9
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f168cb864f9
RDX: 0000000000000010 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007f168cbca568 R08: 00007f168cbca598 R09: 00007f168cbca598
R10: 00007f168cbca598 R11: 0000000000000246 R12: 00007f168cbca3d8
R13: 00007f168cbca4e9 R14: 0000000000000001 R15: 0000000000000003
 </TASK>

The buggy address belongs to the physical page:
page:ffffea00047a4880 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x11e922
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 ffffea0004965748 ffffea00047d1448 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 0x8140dca(GFP_HIGHUSER_MOVABLE|__GFP_COMP|__GFP_ZERO|__GFP_CMA), pid 234, tgid 234 (sshd), ts 14763633216, free_ts 14830909753
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x213/0x220 mm/page_alloc.c:2637
 prep_new_page+0x1b/0x110 mm/page_alloc.c:2644
 get_page_from_freelist+0x3a98/0x3b10 mm/page_alloc.c:4539
 __alloc_pages+0x234/0x610 mm/page_alloc.c:5837
 __folio_alloc+0x15/0x40 mm/page_alloc.c:5869
 __folio_alloc_node include/linux/gfp.h:245 [inline]
 folio_alloc include/linux/gfp.h:274 [inline]
 alloc_page_vma include/linux/gfp.h:283 [inline]
 do_anonymous_page mm/memory.c:4269 [inline]
 handle_pte_fault mm/memory.c:5155 [inline]
 __handle_mm_fault mm/memory.c:5299 [inline]
 handle_mm_fault+0x1cf7/0x30e0 mm/memory.c:5439
 do_user_addr_fault arch/x86/mm/fault.c:1323 [inline]
 handle_page_fault arch/x86/mm/fault.c:1466 [inline]
 exc_page_fault+0x3b3/0x6d0 arch/x86/mm/fault.c:1522
 asm_exc_page_fault+0x27/0x30 arch/x86/include/asm/idtentry.h:608
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 free_pages_prepare mm/page_alloc.c:1545 [inline]
 free_pcp_prepare mm/page_alloc.c:1619 [inline]
 free_unref_page_prepare+0x9f1/0xa00 mm/page_alloc.c:3581
 free_unref_page_list+0xf1/0x7b0 mm/page_alloc.c:3729
 release_pages+0xef9/0xf50 mm/swap.c:1043
 free_pages_and_swap_cache+0x8a/0xa0 mm/swap_state.c:315
 tlb_batch_pages_flush mm/mmu_gather.c:59 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:254 [inline]
 tlb_flush_mmu mm/mmu_gather.c:261 [inline]
 tlb_finish_mmu+0x1e0/0x3f0 mm/mmu_gather.c:361
 unmap_region+0x2c1/0x310 mm/mmap.c:2402
 do_mas_align_munmap+0xd27/0x13a0 mm/mmap.c:2668
 do_mas_munmap+0x23e/0x2b0 mm/mmap.c:2726
 __vm_munmap+0x263/0x3a0 mm/mmap.c:3025
 __do_sys_munmap mm/mmap.c:3051 [inline]
 __se_sys_munmap mm/mmap.c:3047 [inline]
 __x64_sys_munmap+0x6b/0x80 mm/mmap.c:3047
 x64_sys_call+0x75/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:12
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x3b/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Memory state around the buggy address:
 ffff88811e921f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88811e921f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88811e922000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff88811e922080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88811e922100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs error (device loop0): ext4_readdir:260: inode #2: block 255: comm syz-executor267: path (unknown): bad entry in directory: rec_len is smaller than minimal - offset=1023, inode=0, rec_len=0, size=1024 fake=0
EXT4-fs (loop0): unmounting files

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
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.