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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: 303d, last: 1d09h
▶ ▼ 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 616d 616d 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 ext4 19 C done 7 21h27m 231d 0/29 upstream: reported C repro on 2025/05/25 18:12
android-5-15 KASAN: use-after-free Read in ext4_ext_insert_extent origin:lts 19 syz 1 191d 205d 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 792d 788d 0/29 auto-obsoleted due to no activity on 2024/02/09 07:34
▶ ▼ Last patch testing requests (8)
Created Duration User Patch Repo Result
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
2025/06/22 01:01 8m retest repro android13-5.10-lts report log
2025/03/29 21:37 9m retest repro android13-5.10-lts report log
2025/03/29 21:37 7m retest repro android13-5.10-lts report log
▶ ▼ Fix bisection attempts (1)
Created Duration User Patch Repo Result
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+0x2841/0x4530 fs/ext4/extents.c:2153
Read of size 241296 at addr ffff88812fe0ec3c by task syz.4.676/2940

CPU: 1 PID: 2940 Comm: syz.4.676 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x169/0x1d8 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0xe2/0x130 mm/kasan/report.c:452
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x280/0x290 mm/kasan/generic.c:189
 memmove+0x2d/0x70 mm/kasan/shadow.c:54
 ext4_ext_insert_extent+0x2841/0x4530 fs/ext4/extents.c:2153
 ext4_ext_map_blocks+0x17b5/0x5d80 fs/ext4/extents.c:4356
 ext4_map_blocks+0x978/0x1bc0 fs/ext4/inode.c:674
 _ext4_get_block+0x1bb/0x4b0 fs/ext4/inode.c:817
 ext4_get_block+0x39/0x50 fs/ext4/inode.c:834
 ext4_block_write_begin+0x567/0x1330 fs/ext4/inode.c:1101
 ext4_write_begin+0x651/0x15a0 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x455/0xe80 fs/ext4/inode.c:3033
 generic_perform_write+0x2be/0x510 mm/filemap.c:3509
 ext4_buffered_write_iter+0x4b8/0x640 fs/ext4/file.c:271
 ext4_file_write_iter+0x536/0x1980 fs/ext4/file.c:-1
 call_write_iter include/linux/fs.h:2066 [inline]
 new_sync_write fs/read_write.c:518 [inline]
 vfs_write+0x725/0xd60 fs/read_write.c:605
 ksys_write+0x140/0x240 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+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f7ff6273749
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:00007f7ff60e3038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f7ff64c9fa0 RCX: 00007f7ff6273749
RDX: 000000000208e24b RSI: 0000200000000040 RDI: 0000000000000005
RBP: 00007f7ff62f7f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7ff64ca038 R14: 00007f7ff64c9fa0 R15: 00007ffd913b9528

The buggy address belongs to the page:
page:ffffea0004bf8380 refcount:2 mapcount:0 mapping:ffff888110717590 index:0x3f pfn:0x12fe0e
aops:def_blk_aops ino:0
flags: 0x4000000000002014(uptodate|lru|private)
raw: 4000000000002014 ffffea0004576bc8 ffffea000494f988 ffff888110717590
raw: 000000000000003f ffff88811c646b28 00000002ffffffff ffff888125ae0000
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff888125ae0000
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 2940, ts 356785234828, free_ts 356710757366
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x179/0x180 mm/page_alloc.c:2462
 get_page_from_freelist+0x2235/0x23d0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x268/0x5f0 mm/page_alloc.c:5370
 __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+0x642/0x930 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+0x212/0x780 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+0x1084/0x4530 fs/ext4/extents.c:2098
 ext4_ext_map_blocks+0x17b5/0x5d80 fs/ext4/extents.c:4356
 ext4_map_blocks+0x978/0x1bc0 fs/ext4/inode.c:674
 _ext4_get_block+0x1bb/0x4b0 fs/ext4/inode.c:817
 ext4_get_block+0x39/0x50 fs/ext4/inode.c:834
 ext4_block_write_begin+0x567/0x1330 fs/ext4/inode.c:1101
 ext4_write_begin+0x651/0x15a0 fs/ext4/ext4_jbd2.h:-1
 ext4_da_write_begin+0x455/0xe80 fs/ext4/inode.c:3033
 generic_perform_write+0x2be/0x510 mm/filemap.c:3509
 ext4_buffered_write_iter+0x4b8/0x640 fs/ext4/file.c:271
 ext4_file_write_iter+0x536/0x1980 fs/ext4/file.c:-1
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+0x2b7/0x2d0 mm/page_alloc.c:3336
 free_unref_page_list+0x12e/0x9b0 mm/page_alloc.c:3443
 release_pages+0xe38/0xe80 mm/swap.c:1103
 free_pages_and_swap_cache+0x86/0xa0 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+0x175/0x300 mm/mmu_gather.c:326
 exit_mmap+0x2fc/0x540 mm/mmap.c:3387
 __mmput+0x93/0x2f0 kernel/fork.c:1153
 mmput+0x4e/0x150 kernel/fork.c:1176
 exit_mm kernel/exit.c:539 [inline]
 do_exit+0x9ae/0x2480 kernel/exit.c:859
 do_group_exit+0x141/0x310 kernel/exit.c:986
 get_signal+0xf7d/0x12e0 kernel/signal.c:2793
 arch_do_signal_or_restart+0xbf/0x10f0 arch/x86/kernel/signal.c:805
 handle_signal_work kernel/entry/common.c:145 [inline]
 exit_to_user_mode_loop+0xa2/0xe0 kernel/entry/common.c:169
 exit_to_user_mode_prepare+0x76/0xa0 kernel/entry/common.c:199
 syscall_exit_to_user_mode+0x1d/0x40 kernel/entry/common.c:274
 do_syscall_64+0x3d/0x40 arch/x86/entry/common.c:56

Memory state around the buggy address:
 ffff88812fe0ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88812fe0ff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88812fe10000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff88812fe10080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88812fe10100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
EXT4-fs error (device loop4): ext4_free_blocks:5685: comm syz.4.676: Freeing blocks not in datazone - block = 2276332667268, count = 9932
EXT4-fs error (device loop4): ext4_free_blocks:5685: comm syz.4.676: Freeing blocks not in datazone - block = 0, count = 192

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
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
2025/03/15 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
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
* Struck through repros no longer work on HEAD.