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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: 36d, last: 21d
▶ ▼ 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 16 8d13h 751d 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 8 18d 723d 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 20 5d13h 147d 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 7 76d 600d 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 599d 773d 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 310d 741d 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 27d 582d 0/3 upstream: reported C repro on 2024/01/21 16:07
▶ ▼ Last patch testing requests (5)
Created Duration User Patch Repo Result
2025/08/04 04:42 6m retest repro android14-6.1 report log
2025/08/04 04:42 7m retest repro android14-6.1 report log
2025/08/04 04:42 7m retest repro android14-6.1 report log
2025/08/04 04:42 10m retest repro android14-6.1 report log
2025/08/04 04:42 7m retest repro android14-6.1 report log

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in ext4_ext_rm_leaf fs/ext4/extents.c:2601 [inline]
BUG: KASAN: use-after-free in ext4_ext_remove_space+0x2f43/0x3fb0 fs/ext4/extents.c:2939
Read of size 4 at addr ffff8881252cddb8 by task syz-executor345/290

CPU: 1 PID: 290 Comm: syz-executor345 Not tainted 6.1.141-syzkaller-00039-g145c7fad733f #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 __dump_stack+0x21/0x24 lib/dump_stack.c:88
 dump_stack_lvl+0xee/0x150 lib/dump_stack.c:106
 print_address_description+0x71/0x210 mm/kasan/report.c:316
 print_report+0x4a/0x60 mm/kasan/report.c:427
 kasan_report+0x122/0x150 mm/kasan/report.c:531
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report_generic.c:350
 ext4_ext_rm_leaf fs/ext4/extents.c:2601 [inline]
 ext4_ext_remove_space+0x2f43/0x3fb0 fs/ext4/extents.c:2939
 ext4_ext_truncate+0x200/0x320 fs/ext4/extents.c:4469
 ext4_truncate+0x9a6/0xf90 fs/ext4/inode.c:4291
 ext4_evict_inode+0xcc3/0x1460 fs/ext4/inode.c:286
 evict+0x493/0x890 fs/inode.c:705
 iput_final fs/inode.c:1834 [inline]
 iput+0x620/0x670 fs/inode.c:1860
 do_unlinkat+0x375/0x6b0 fs/namei.c:4396
 __do_sys_unlink fs/namei.c:4437 [inline]
 __se_sys_unlink fs/namei.c:4435 [inline]
 __x64_sys_unlink+0x49/0x50 fs/namei.c:4435
 x64_sys_call+0x958/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:88
 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: 0033:0x7f28f287bd17
Code: 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 57 00 00 00 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:00007ffd410e29d8 EFLAGS: 00000206 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f28f287bd17
RDX: 00007ffd410e2a00 RSI: 00007ffd410e2a90 RDI: 00007ffd410e2a90
RBP: 00007ffd410e2a90 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000100 R11: 0000000000000206 R12: 00007ffd410e3b80
R13: 000055558a51a700 R14: 431bde82d7b634db R15: 00007ffd410e4c10
 </TASK>

The buggy address belongs to the physical page:
page:ffffea000494b340 refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x1252cd
flags: 0x4000000000000000(zone=1)
raw: 4000000000000000 ffffea000494b388 ffffea000494b308 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 292, tgid 292 (syz-executor345), ts 25028822502, free_ts 25354457353
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f5/0x210 mm/page_alloc.c:2637
 prep_new_page+0x1c/0x110 mm/page_alloc.c:2644
 get_page_from_freelist+0x2c7b/0x2cf0 mm/page_alloc.c:4539
 __alloc_pages+0x19e/0x3a0 mm/page_alloc.c:5850
 __folio_alloc+0x12/0x40 mm/page_alloc.c:5882
 __folio_alloc_node include/linux/gfp.h:245 [inline]
 folio_alloc include/linux/gfp.h:274 [inline]
 shmem_alloc_folio mm/shmem.c:1601 [inline]
 shmem_alloc_and_acct_folio+0x650/0x870 mm/shmem.c:1626
 shmem_get_folio_gfp+0x119f/0x2230 mm/shmem.c:1955
 shmem_get_folio mm/shmem.c:2086 [inline]
 shmem_write_begin+0xea/0x2c0 mm/shmem.c:2571
 generic_perform_write+0x2f6/0x6d0 mm/filemap.c:3882
 __generic_file_write_iter+0x227/0x580 mm/filemap.c:4011
 generic_file_write_iter+0xae/0x310 mm/filemap.c:4043
 call_write_iter include/linux/fs.h:2282 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x5db/0xca0 fs/read_write.c:584
 ksys_write+0x140/0x240 fs/read_write.c:637
 __do_sys_write fs/read_write.c:649 [inline]
 __se_sys_write fs/read_write.c:646 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:646
 x64_sys_call+0x27b/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:2
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
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+0x742/0x750 mm/page_alloc.c:3581
 free_unref_page_list+0xba/0x7c0 mm/page_alloc.c:3729
 release_pages+0xad1/0xb20 mm/swap.c:1043
 __pagevec_release+0x71/0xe0 mm/swap.c:1063
 pagevec_release include/linux/pagevec.h:71 [inline]
 folio_batch_release include/linux/pagevec.h:135 [inline]
 shmem_undo_range+0x51a/0x1470 mm/shmem.c:955
 shmem_truncate_range mm/shmem.c:1071 [inline]
 shmem_evict_inode+0x242/0xa10 mm/shmem.c:1180
 evict+0x493/0x890 fs/inode.c:705
 iput_final fs/inode.c:1834 [inline]
 iput+0x620/0x670 fs/inode.c:1860
 dentry_unlink_inode+0x33d/0x3f0 fs/dcache.c:405
 __dentry_kill+0x460/0x670 fs/dcache.c:611
 dentry_kill+0xc0/0x2a0 fs/dcache.c:-1
 dput+0x42/0x80 fs/dcache.c:918
 __fput+0x5be/0x8f0 fs/file_table.c:328
 ____fput+0x15/0x20 fs/file_table.c:348
 task_work_run+0x1db/0x240 kernel/task_work.c:203
 ptrace_notify+0x221/0x250 kernel/signal.c:2377

Memory state around the buggy address:
 ffff8881252cdc80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881252cdd00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8881252cdd80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                        ^
 ffff8881252cde00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881252cde80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs (loop0): unmounting filesystem.
EXT4-fs (loop0): unmounting filesystem.
EXT4-fs (loop0): unmounting filesystem.
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 1121070427392, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 1121070426627, count = 772
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 1121070426624, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 6296506030080, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 6296506009100, count = 20995
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 6296506009088, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 1121070428672, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 1121070427907, count = 772
EXT4-fs (loop0): unmounting filesystem.
EXT4-fs (loop0): unmounting filesystem.
EXT4-fs (loop0): unmounting filesystem.
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 115750969595360, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 115750969565550, count = 29811
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 115750969565536, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 435390827168, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 435390797381, count = 29793
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 435390797376, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 75176748627888, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 75176748607337, count = 20566
EXT4-fs (loop0): unmounting filesystem.
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 2564649124240, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 2564649123955, count = 290
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 3846, count = 0
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 3840, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 52781440325632, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 52781440303104, count = 22529
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 175934745372720, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 175934745370346, count = 2386
EXT4-fs (loop0): unmounting filesystem.
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 145199959378768, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 145199959377500, count = 1272
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 145199959377488, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 144318559300976, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 144318559289343, count = 11636
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 144318559289328, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 1408828379520, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 1408828379072, count = 453
EXT4-fs (loop0): unmounting filesystem.
EXT4-fs (loop0): unmounting filesystem.
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 1657912335, count = 0
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 1657912320, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 259287954137760, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 259287954122388, count = 15375
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 259287954122384, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 213871852398880, count = 19969
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 213871852398880, count = 16
EXT4-fs error (device loop0): ext4_free_blocks:6210: comm syz-executor345: Freeing blocks not in datazone - block = 16930761109760, count = 16

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
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.