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KASAN: use-after-free Read in ext4_find_extent (2)

Status: upstream: reported C repro on 2025/05/31 08:45
Bug presence: origin:lts
[Documentation on labels]
Reported-by: syzbot+869401e856e234844286@syzkaller.appspotmail.com
First crash: 252d, last: 2d02h
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/06/01 lts (merge base) 02b72ccb5f9d C [report] KASAN: use-after-free Read in ext4_find_extent
2025/06/01 upstream (ToT) cd2e103d57e5 C Didn't crash
▶ ▼ Similar bugs (12)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-54 KASAN: use-after-free Read in ext4_find_extent 19 C 2 260d 358d 0/2 upstream: reported C repro on 2025/02/13 21:05
android-5-10 KASAN: use-after-free Read in ext4_find_extent ext4 19 C error inconclusive 84 2d15h 1139d 0/2 upstream: reported C repro on 2022/12/26 07:59
android-6-1 KASAN: use-after-free Read in ext4_find_extent missing-backport 19 C error done 3 468d 965d 0/2 auto-obsoleted due to no activity on 2025/02/04 04:57
linux-5.15 KASAN: use-after-free Read in ext4_find_extent origin:lts-only 19 C inconclusive 7 45d 933d 0/3 upstream: reported C repro on 2023/07/19 14:49
linux-6.6 KASAN: use-after-free Read in ext4_find_extent origin:upstream 19 C error 8 43d 43d 0/2 upstream: reported C repro on 2025/12/25 19:30
upstream KASAN: use-after-free Read in ext4_find_extent ext4 19 2 1571d 1632d 0/29 auto-closed as invalid on 2022/02/17 05:19
linux-6.1 KASAN: use-after-free Read in ext4_find_extent origin:upstream missing-backport 19 C done 62 132d 872d 0/3 upstream: reported C repro on 2023/09/19 00:11
android-5-15 KASAN: use-after-free Read in ext4_find_extent ext4 origin:lts 19 C error 113 11d 1139d 0/2 upstream: reported C repro on 2022/12/26 07:59
upstream KASAN: use-after-free Read in ext4_find_extent (2) ext4 19 C error 2 1009d 1134d 22/29 fixed on 2023/06/08 14:41
upstream KASAN: use-after-free Read in ext4_find_extent (4) ext4 19 C done 236 2d09h 403d 0/29 upstream: reported C repro on 2024/12/30 20:06
upstream KASAN: use-after-free Read in ext4_find_extent (3) prio:low ext4 19 C error done 31 774d 955d 25/29 fixed on 2024/01/30 23:26
android-54 KASAN: slab-out-of-bounds Read in ext4_find_extent ext4 17 C 1 953d 1139d 0/2 auto-obsoleted due to no activity on 2023/10/08 03:20
▶ ▼ Last patch testing requests (9)
Created Duration User Patch Repo Result
2026/02/01 04:45 6m retest repro android14-6.1 report log
2026/02/01 04:45 30m retest repro android14-6.1 report log
2026/02/01 04:45 40m retest repro android14-6.1 report log
2026/02/01 04:45 19m retest repro android14-6.1 report log
2026/02/01 04:45 7m retest repro android14-6.1 report log
2026/01/15 01:26 15m retest repro android14-6.1 report log
2026/01/15 01:26 19m retest repro android14-6.1 report log
2025/12/16 08:24 6m retest repro android14-6.1 report log
2025/12/16 08:24 1h15m retest repro android14-6.1 report log
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2025/07/31 06:27 1h21m bisect fix android14-6.1 OK (0) job log log
2025/06/30 20:17 1h08m bisect fix android14-6.1 OK (0) job log log

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:953
Read of size 4 at addr ffff88812edefe18 by task kworker/u4:3/326

CPU: 1 PID: 326 Comm: kworker/u4:3 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: writeback wb_workfn (flush-7:2)
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_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:350
 ext4_ext_binsearch fs/ext4/extents.c:837 [inline]
 ext4_find_extent+0xbeb/0xe20 fs/ext4/extents.c:953
 ext4_ext_map_blocks+0x207/0x61d0 fs/ext4/extents.c:4166
 ext4_map_blocks+0x9d8/0x1b70 fs/ext4/inode.c:679
 mpage_map_one_extent fs/ext4/inode.c:2435 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2488 [inline]
 ext4_writepages+0x1409/0x30e0 fs/ext4/inode.c:2856
 do_writepages+0x3a4/0x5f0 mm/page-writeback.c:2494
 __writeback_single_inode+0xc6/0xad0 fs/fs-writeback.c:1622
 writeback_sb_inodes+0xa10/0x15d0 fs/fs-writeback.c:1913
 wb_writeback+0x40b/0x9d0 fs/fs-writeback.c:2089
 wb_do_writeback fs/fs-writeback.c:2236 [inline]
 wb_workfn+0x378/0xeb0 fs/fs-writeback.c:2276
 process_one_work+0x71f/0xc40 kernel/workqueue.c:2302
 worker_thread+0xa29/0x11e0 kernel/workqueue.c:2449
 kthread+0x281/0x320 kernel/kthread.c:386
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0004bb7bc0 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x12edef
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 ffffea0004bb5748 ffffea0004bb7b48 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 0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid 380, tgid 380 (syz-executor), ts 28979855549, free_ts 29045941344
 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
 __folio_alloc+0x12/0x40 mm/page_alloc.c:5900
 __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]
 wp_page_copy+0x2a3/0x15a0 mm/memory.c:3210
 do_wp_page+0x9f2/0xfc0 mm/memory.c:-1
 handle_pte_fault mm/memory.c:5189 [inline]
 __handle_mm_fault mm/memory.c:5313 [inline]
 handle_mm_fault+0x1124/0x26c0 mm/memory.c:5453
 do_user_addr_fault+0x905/0x1050 arch/x86/mm/fault.c:1323
 handle_page_fault arch/x86/mm/fault.c:1466 [inline]
 exc_page_fault+0x51/0xb0 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:1551 [inline]
 free_pcp_prepare mm/page_alloc.c:1625 [inline]
 free_unref_page_prepare+0x742/0x750 mm/page_alloc.c:3589
 free_unref_page_list+0x117/0x8c0 mm/page_alloc.c:3740
 release_pages+0xaf2/0xb50 mm/swap.c:1048
 free_pages_and_swap_cache+0x86/0xa0 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+0x1aa/0x370 mm/mmu_gather.c:361
 exit_mmap+0x412/0xc10 mm/mmap.c:3384
 __mmput+0x93/0x360 kernel/fork.c:1309
 mmput+0x4b/0x150 kernel/fork.c:1333
 exit_mm kernel/exit.c:568 [inline]
 do_exit+0x994/0x2660 kernel/exit.c:873
 do_group_exit+0x210/0x2d0 kernel/exit.c:1028
 __do_sys_exit_group kernel/exit.c:1039 [inline]
 __se_sys_exit_group kernel/exit.c:1037 [inline]
 __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1037
 x64_sys_call+0x7b4/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:232
 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

Memory state around the buggy address:
 ffff88812edefd00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812edefd80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88812edefe00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff88812edefe80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812edeff00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs error (device loop2): ext4_map_blocks:745: inode #15: comm kworker/u4:3: lblock 0 mapped to illegal pblock 0 (length 1)
EXT4-fs (loop2): Remounting filesystem read-only
EXT4-fs error (device loop2): ext4_map_blocks:745: inode #15: block 71748523475265: comm kworker/u4:3: lblock 0 mapped to illegal pblock 71748523475265 (length 1)
EXT4-fs (loop2): Remounting filesystem read-only
EXT4-fs error (device loop2): ext4_map_blocks:745: inode #15: block 512: comm kworker/u4:3: lblock 0 mapped to illegal pblock 512 (length 1)
EXT4-fs (loop2): Remounting filesystem read-only
EXT4-fs error (device loop2): ext4_map_blocks:745: inode #15: block 118173431786593: comm kworker/u4:3: lblock 0 mapped to illegal pblock 118173431786593 (length 1)
EXT4-fs (loop2): Remounting filesystem read-only
EXT4-fs error (device loop2): ext4_map_blocks:745: inode #15: block 1653562406152: comm kworker/u4:3: lblock 0 mapped to illegal pblock 1653562406152 (length 1)
EXT4-fs (loop2): Remounting filesystem read-only
EXT4-fs error (device loop2): ext4_map_blocks:745: inode #15: block 126969739568179: comm kworker/u4:3: lblock 0 mapped to illegal pblock 126969739568179 (length 1)
EXT4-fs (loop2): Remounting filesystem read-only
EXT4-fs error (device loop2): ext4_map_blocks:745: inode #15: block 161344741474247: comm kworker/u4:3: lblock 0 mapped to illegal pblock 161344741474247 (length 1)
EXT4-fs (loop2): Remounting filesystem read-only
EXT4-fs error (device loop2): ext4_map_blocks:745: inode #15: block 71748523475265: comm kworker/u4:3: lblock 0 mapped to illegal pblock 71748523475265 (length 1)
EXT4-fs (loop2): Remounting filesystem read-only

Crashes (22):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/05 08:55 android14-6.1 775f23d50ca8 ea10c935 .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_find_extent
2026/01/17 19:05 android14-6.1 f8a5ad1fcf13 20d37d28 .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_find_extent
2025/10/24 04:04 android14-6.1 22c0b7236c43 c0460fcd .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_find_extent
2025/10/24 03:23 android14-6.1 22c0b7236c43 c0460fcd .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_find_extent
2025/10/24 02:37 android14-6.1 22c0b7236c43 c0460fcd .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_find_extent
2025/09/29 02:17 android14-6.1 5303560ee8cf 001c9061 .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_find_extent
2025/09/03 14:52 android14-6.1 79ccb6ecf51e 96a211bc .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_find_extent
2025/08/03 17:31 android14-6.1 3b4ff5af8d36 7368264b .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_find_extent
2025/05/31 08:37 android14-6.1 db710ea87c32 3d2f584d .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_find_extent
2025/11/22 21:09 android14-6.1 eba111621724 4fb8ef37 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/12/30 18:59 android14-6.1 5e6db7045704 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/12/30 18:59 android14-6.1 5e6db7045704 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/12/30 18:58 android14-6.1 5e6db7045704 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/12/30 18:57 android14-6.1 5e6db7045704 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/12/01 12:36 android14-6.1 a92da54b7708 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/11/30 15:55 android14-6.1 a92da54b7708 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/09/14 09:34 android14-6.1 0429b7af308c e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/08/28 01:48 android14-6.1 47b374a18638 e12e5ba4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/08/28 01:48 android14-6.1 47b374a18638 e12e5ba4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/08/28 01:46 android14-6.1 47b374a18638 e12e5ba4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/08/28 01:46 android14-6.1 47b374a18638 e12e5ba4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
2025/05/31 08:03 android14-6.1 db710ea87c32 3d2f584d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_find_extent
* Struck through repros no longer work on HEAD.