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KASAN: use-after-free Read in ext4_ext_remove_space

Status: upstream: reported C repro on 2025/07/20 13:48
Bug presence: origin:lts
[Documentation on labels]
Reported-by: syzbot+8ecc8500ff5712c63801@syzkaller.appspotmail.com
First crash: 183d, last: 1d14h
Fix bisection: failed (error log)
  
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/07/20 lts (merge base) 58485ff1a74f C [report] KASAN: use-after-free Read in ext4_ext_remove_space
2025/07/20 upstream (ToT) 5f054ef2e0f1 C Didn't crash
▶ ▼ Similar bugs (7)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-15 KASAN: out-of-bounds Read in ext4_ext_remove_space origin:upstream missing-backport 24 C error error 30 6d13h 899d 0/2 upstream: reported C repro on 2023/08/04 22:38
android-5-10 KASAN: out-of-bounds Read in ext4_ext_remove_space 24 C error 42 7h16m 870d 0/2 upstream: reported C repro on 2023/09/02 13:17
upstream KASAN: slab-use-after-free Read in ext4_ext_remove_space ext4 19 C error 43 4d04h 294d 0/29 upstream: reported C repro on 2025/03/31 11:15
linux-6.1 KASAN: out-of-bounds Read in ext4_ext_remove_space origin:upstream missing-backport 19 C done 9 35d 747d 0/3 upstream: reported C repro on 2024/01/03 15:27
upstream KASAN: out-of-bounds Read in ext4_ext_remove_space ext4 17 C error done 8 746d 920d 25/29 fixed on 2024/02/16 19:40
android-6-1 KASAN: out-of-bounds Read in ext4_ext_remove_space missing-backport 17 C error error 6 457d 889d 0/2 auto-obsoleted due to no activity on 2025/01/27 17:01
linux-5.15 KASAN: out-of-bounds Read in ext4_ext_remove_space missing-backport origin:upstream 17 C done 5 33d 729d 0/3 upstream: reported C repro on 2024/01/21 16:07
▶ ▼ Last patch testing requests (8)
Created Duration User Patch Repo Result
2025/12/24 21:47 12m retest repro android14-6.1 report log
2025/12/24 21:47 12m retest repro android14-6.1 report log
2025/12/24 21:47 13m retest repro android14-6.1 report log
2025/12/24 21:47 14m retest repro android14-6.1 report log
2025/10/14 18:04 7m retest repro android14-6.1 report log
2025/10/14 18:04 8m retest repro android14-6.1 report log
2025/10/14 18:04 6m retest repro android14-6.1 report log
2025/10/14 18:04 11m retest repro android14-6.1 report log
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2025/11/18 21:12 0m bisect fix android14-6.1 error
2025/09/13 14:37 1h52m bisect fix android14-6.1 OK (0) job log log

Sample crash report:
         and is ignored by this kernel. Remove the mand
         option from the mount to silence this warning.
=======================================================
EXT4-fs: Ignoring removed oldalloc option
EXT4-fs: Ignoring removed orlov option
EXT4-fs (loop2): mounted filesystem without journal. Quota mode: writeback.
==================================================================
BUG: KASAN: use-after-free in ext4_ext_rm_leaf fs/ext4/extents.c:2602 [inline]
BUG: KASAN: use-after-free in ext4_ext_remove_space+0x348b/0x40d0 fs/ext4/extents.c:2940
Read of size 4 at addr ffff888129381c18 by task syz.2.17/373

CPU: 1 PID: 373 Comm: syz.2.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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_rm_leaf fs/ext4/extents.c:2602 [inline]
 ext4_ext_remove_space+0x348b/0x40d0 fs/ext4/extents.c:2940
 ext4_ext_truncate+0x200/0x320 fs/ext4/extents.c:4470
 ext4_truncate+0x9be/0xfb0 fs/ext4/inode.c:4297
 ext4_setattr+0x10f1/0x1a60 fs/ext4/inode.c:5647
 notify_change+0xcc3/0xf80 fs/attr.c:499
 do_truncate+0x1ac/0x240 fs/open.c:66
 handle_truncate fs/namei.c:3292 [inline]
 do_open fs/namei.c:3637 [inline]
 path_openat+0x28f0/0x2f80 fs/namei.c:3790
 do_filp_open+0x1f1/0x430 fs/namei.c:3817
 do_sys_openat2+0x15e/0x810 fs/open.c:1341
 do_sys_open fs/open.c:1357 [inline]
 __do_sys_creat fs/open.c:1435 [inline]
 __se_sys_creat fs/open.c:1429 [inline]
 __x64_sys_creat+0x8e/0xb0 fs/open.c:1429
 x64_sys_call+0x116/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:86
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f0bf539acb9
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:00007ffc62a8bcf8 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
RAX: ffffffffffffffda RBX: 00007f0bf5615fa0 RCX: 00007f0bf539acb9
RDX: 0000000000000000 RSI: 0000000000000108 RDI: 0000200000000680
RBP: 00007f0bf5408bf7 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0bf5615fac R14: 00007f0bf5615fa0 R15: 00007f0bf5615fa0
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0004a4e040 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x129381
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 dead000000000100 dead000000000122 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 292, tgid 292 (syz-executor), ts 23190005450, free_ts 24742831008
 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]
 do_anonymous_page mm/memory.c:4283 [inline]
 handle_pte_fault mm/memory.c:5169 [inline]
 __handle_mm_fault mm/memory.c:5313 [inline]
 handle_mm_fault+0x1972/0x26c0 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
 unmap_region+0x2b7/0x320 mm/mmap.c:2419
 do_mas_align_munmap+0xbed/0x1320 mm/mmap.c:2693
 do_mas_munmap+0x241/0x2b0 mm/mmap.c:2751
 __vm_munmap+0x1bd/0x330 mm/mmap.c:3050
 __do_sys_munmap mm/mmap.c:3076 [inline]
 __se_sys_munmap mm/mmap.c:3072 [inline]
 __x64_sys_munmap+0x6b/0x80 mm/mmap.c:3072
 x64_sys_call+0x8a/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:12
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Memory state around the buggy address:
 ffff888129381b00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888129381b80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888129381c00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                            ^
 ffff888129381c80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888129381d00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 55183558011280, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 55183557996849, count = 14437
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 55183557996848, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 104592811931504, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 104592811909983, count = 21536
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 104592811909968, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 112589185194640, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 112589185168440, count = 26214
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 112589185168432, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 119254237302208, count = 16
EXT4-fs error: 33014 callbacks suppressed
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 62012422014864, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 62012421988660, count = 26214
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 62012421988656, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 119251478963920, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 119251478934388, count = 29541
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 119251478934384, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 111499019535056, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 111499019509604, count = 25459
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 111499019509600, count = 16
EXT4-fs error (device loop2): ext4_free_blocks:6205: comm syz.2.17: Freeing blocks not in datazone - block = 109260482075072, count = 16

Crashes (8):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/18 08:52 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_ext_remove_space
2026/01/17 11:11 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_ext_remove_space
2025/07/20 17:34 android14-6.1 145c7fad733f 7117feec .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_ext_remove_space
2025/07/20 16:23 android14-6.1 145c7fad733f 7117feec .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_ext_remove_space
2025/07/20 15:35 android14-6.1 145c7fad733f 7117feec .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_ext_remove_space
2025/07/20 14:43 android14-6.1 145c7fad733f 7117feec .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_ext_remove_space
2025/07/20 13:37 android14-6.1 145c7fad733f 7117feec .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_ext_remove_space
2025/07/20 12:27 android14-6.1 145c7fad733f 7117feec .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-1 KASAN: use-after-free Read in ext4_ext_remove_space
* Struck through repros no longer work on HEAD.