KASAN: use-after-free Read in ext4_ext_insert_extent

Status: premoderation: reported syz repro on 2025/03/14 06:10
Reported-by: syzbot+de7ff4a74549b4767b3d@syzkaller.appspotmail.com
First crash: 498d, last: 30d
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 KASAN: use-after-free Read in ext4_ext_insert_extent 19 1 811d 811d 0/3 auto-obsoleted due to no activity on 2024/08/13 04:16
upstream KASAN: use-after-free Read in ext4_ext_insert_extent prio:high ext4 22 C done error 10 142d 425d 0/29 auto-obsoleted due to no activity on 2026/06/13 09:21
android-5-15 KASAN: use-after-free Read in ext4_ext_insert_extent origin:lts 19 syz error 3 94d 400d 0/2 premoderation: reported syz repro on 2025/06/20 07:17
upstream KASAN: slab-use-after-free Read in ext4_ext_insert_extent ext4 19 1 987d 983d 0/29 auto-obsoleted due to no activity on 2024/02/09 07:34
▶ ▼ Last patch testing requests (10)
Created Duration User Patch Repo Result
2026/07/24 06:01 14m retest repro android13-5.10-lts log
2026/04/19 07:05 16m retest repro android13-5.10-lts report log
2026/02/07 22:41 10m retest repro android13-5.10-lts report log
2026/01/24 17:54 12m retest repro android13-5.10-lts report log
2026/01/24 17:47 11m retest repro android13-5.10-lts OK log
2026/01/05 14:30 7m retest repro android13-5.10-lts report log
2025/11/18 06:01 7m retest repro android13-5.10-lts report log
2025/10/26 18:13 7m retest repro android13-5.10-lts report log
2025/09/07 20:41 35m retest repro android13-5.10-lts report log
2025/08/16 18:36 16m retest repro android13-5.10-lts report log
▶ ▼ Fix bisection attempts (5)
Created Duration User Patch Repo Result
2026/06/24 11:42 3h01m bisect fix android13-5.10-lts OK (0) job log log
2026/05/19 08:00 1h22m bisect fix android13-5.10-lts OK (0) job log log
2026/04/04 21:13 2h16m bisect fix android13-5.10-lts OK (0) job log log
2026/02/23 18:49 1h02m bisect fix android13-5.10-lts OK (0) job log log
2025/06/07 14:12 1h35m bisect fix android13-5.10-lts OK (0) job log log

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in ext4_ext_insert_extent+0x2a72/0x4c30 fs/ext4/extents.c:2152
Read of size 332280 at addr ffff888130e04c3c by task syz.3.19/442

CPU: 0 PID: 442 Comm: syz.3.19 Not tainted 5.10.234-syzkaller-00031-gfc9aa81462ee #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack_lvl+0x1e2/0x24b lib/dump_stack.c:118
 print_address_description+0x81/0x3b0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0x179/0x1c0 mm/kasan/report.c:452
 kasan_check_range+0x293/0x2a0 mm/kasan/generic.c:189
 memmove+0x2d/0x70 mm/kasan/shadow.c:54
 ext4_ext_insert_extent+0x2a72/0x4c30 fs/ext4/extents.c:2152
 ext4_ext_map_blocks+0x1c47/0x6ee0 fs/ext4/extents.c:4354
 ext4_map_blocks+0xa65/0x1d10 fs/ext4/inode.c:673
 _ext4_get_block+0x21b/0x610 fs/ext4/inode.c:816
 ext4_get_block+0x39/0x50 fs/ext4/inode.c:833
 ext4_block_write_begin+0x61e/0x13b0 fs/ext4/inode.c:1100
 ext4_write_begin+0x6fa/0x1730
 ext4_da_write_begin+0x49d/0xf60 fs/ext4/inode.c:3032
 generic_perform_write+0x2cd/0x570 mm/filemap.c:3509
 ext4_buffered_write_iter+0x482/0x610 fs/ext4/file.c:271
 ext4_file_write_iter+0x193/0x1c80 fs/ext4/file.c:685
 call_write_iter include/linux/fs.h:2058 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0xb4c/0xe70 fs/read_write.c:605
 ksys_write+0x199/0x2c0 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:667
 do_syscall_64+0x34/0x70
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7fc187144169
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fc186b95038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fc18735d080 RCX: 00007fc187144169
RDX: 00000000002a979d RSI: 0000400000000000 RDI: 0000000000000004
RBP: 00007fc1871c52a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fc18735d080 R15: 00007ffe3cd51438

The buggy address belongs to the page:
page:ffffea0004c38100 refcount:2 mapcount:0 mapping:ffff888110315390 index:0x3f pfn:0x130e04
aops:def_blk_aops ino:0
flags: 0x4000000000002014(uptodate|lru|private)
raw: 4000000000002014 ffffea0004514cc8 ffffea000499f548 ffff888110315390
raw: 000000000000003f ffff888128321888 00000002ffffffff ffff88812730c000
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff88812730c000
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Movable, gfp_mask 0x108c48(GFP_NOFS|__GFP_NOFAIL|__GFP_HARDWALL|__GFP_MOVABLE), pid 442, ts 27122776141, free_ts 26831176483
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x166/0x180 mm/page_alloc.c:2462
 get_page_from_freelist+0x2d8c/0x2f30 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x435/0xaf0 mm/page_alloc.c:5348
 __alloc_pages include/linux/gfp.h:544 [inline]
 __alloc_pages_node include/linux/gfp.h:557 [inline]
 alloc_pages_node include/linux/gfp.h:571 [inline]
 alloc_pages include/linux/gfp.h:590 [inline]
 __page_cache_alloc include/linux/pagemap.h:290 [inline]
 pagecache_get_page+0x669/0x950 mm/filemap.c:1848
 find_or_create_page include/linux/pagemap.h:402 [inline]
 grow_dev_page fs/buffer.c:976 [inline]
 grow_buffers fs/buffer.c:1045 [inline]
 __getblk_slow fs/buffer.c:1072 [inline]
 __getblk_gfp+0x221/0x7e0 fs/buffer.c:1370
 sb_getblk_gfp include/linux/buffer_head.h:368 [inline]
 ext4_ext_grow_indepth fs/ext4/extents.c:1327 [inline]
 ext4_ext_create_new_leaf fs/ext4/extents.c:1426 [inline]
 ext4_ext_insert_extent+0xf33/0x4c30 fs/ext4/extents.c:2097
 ext4_ext_map_blocks+0x1c47/0x6ee0 fs/ext4/extents.c:4354
 ext4_map_blocks+0xa65/0x1d10 fs/ext4/inode.c:673
 _ext4_get_block+0x21b/0x610 fs/ext4/inode.c:816
 ext4_get_block+0x39/0x50 fs/ext4/inode.c:833
 ext4_block_write_begin+0x61e/0x13b0 fs/ext4/inode.c:1100
 ext4_write_begin+0x6fa/0x1730
 ext4_da_write_begin+0x49d/0xf60 fs/ext4/inode.c:3032
 generic_perform_write+0x2cd/0x570 mm/filemap.c:3509
 ext4_buffered_write_iter+0x482/0x610 fs/ext4/file.c:271
 ext4_file_write_iter+0x193/0x1c80 fs/ext4/file.c:685
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:28 [inline]
 free_pages_prepare mm/page_alloc.c:1349 [inline]
 free_pcp_prepare mm/page_alloc.c:1421 [inline]
 free_unref_page_prepare+0x2ae/0x2d0 mm/page_alloc.c:3336
 free_unref_page_list+0x122/0xb20 mm/page_alloc.c:3443
 release_pages+0xea0/0xef0 mm/swap.c:1103
 free_pages_and_swap_cache+0x8a/0xa0 mm/swap_state.c:356
 tlb_batch_pages_flush mm/mmu_gather.c:49 [inline]
 tlb_flush_mmu_free mm/mmu_gather.c:240 [inline]
 tlb_flush_mmu mm/mmu_gather.c:247 [inline]
 tlb_finish_mmu+0x177/0x320 mm/mmu_gather.c:326
 exit_mmap+0x306/0x560 mm/mmap.c:3375
 __mmput+0x95/0x2d0 kernel/fork.c:1153
 mmput+0x59/0x170 kernel/fork.c:1176
 exit_mm kernel/exit.c:539 [inline]
 do_exit+0xbda/0x2a50 kernel/exit.c:850
 do_group_exit+0x141/0x310 kernel/exit.c:985
 get_signal+0x10a0/0x1410 kernel/signal.c:2793
 arch_do_signal_or_restart+0xbd/0x17c0 arch/x86/kernel/signal.c:805
 handle_signal_work kernel/entry/common.c:145 [inline]
 exit_to_user_mode_loop+0x9b/0xd0 kernel/entry/common.c:169
 exit_to_user_mode_prepare kernel/entry/common.c:199 [inline]
 syscall_exit_to_user_mode+0xa2/0x1a0 kernel/entry/common.c:274
 do_syscall_64+0x40/0x70 arch/x86/entry/common.c:56
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Memory state around the buggy address:
 ffff888130e09f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888130e09f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888130e0a000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
                   ^
 ffff888130e0a080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888130e0a100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/03/15 19:16 android13-5.10-lts fc9aa81462ee e2826670 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci2-android-5-10 KASAN: use-after-free Read in ext4_ext_insert_extent
2025/03/14 06:09 android13-5.10-lts 3f5f2283d684 e2826670 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci2-android-5-10 KASAN: use-after-free Read in ext4_ext_insert_extent
2026/01/10 17:00 android13-5.10-lts e253c52bbdfc d6526ea3 .config console log report syz / log [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci2-android-5-10 KASAN: use-after-free Read in ext4_ext_insert_extent
2025/11/26 22:22 android13-5.10-lts 9286af17ed5f d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in ext4_ext_insert_extent
2026/03/05 21:02 android13-5.10-lts dad37bbb13a8 d20b04c8 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: slab-out-of-bounds Read in ext4_ext_insert_extent
* Struck through repros no longer work on HEAD.