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

Status: fixed on 2023/06/08 14:41
Subsystems: ext4
[Documentation on labels]
Reported-by: syzbot+bf4bb7731ef73b83a3b4@syzkaller.appspotmail.com
Fix commit: 835659598c67 ext4: fix use-after-free read in ext4_find_extent for bigalloc + inline
First crash: 1317d, last: 1188d
Cause bisection: failed (error log, bisect log)
  
▶ ▼ Discussions (5)
Title Replies (including bot) Last reply
Re: [RESEND PATCH] ext4: fix use-after-free Read in ext4_find_extent for bigalloc + inline 1 (1) 2023/04/30 17:59
[RESEND PATCH] ext4: fix use-after-free Read in ext4_find_extent for bigalloc + inline 1 (1) 2023/04/06 11:16
[PATCH] ext4: fix use-after-free Read in ext4_find_extent for bigalloc + inline 4 (4) 2023/03/03 01:12
[PATCH] ext4: Verify extent header in ext4_find_extent() 3 (3) 2023/01/03 17:33
[syzbot] [ext4?] KASAN: use-after-free Read in ext4_find_extent (2) 0 (1) 2022/12/31 07:08
▶ ▼ 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 syz, C 2 439d 537d 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 syz, C error inconclusive 141 2d13h 1318d 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 syz, C error done 3 647d 1144d 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 syz, C inconclusive 7 35d 1112d 0/3 upstream: reported C repro on 2023/07/19 14:49
linux-6.6 KASAN: use-after-free Read in ext4_find_extent 19 syz, C error 8 221d 222d 0/2 auto-obsoleted due to no activity on 2026/04/15 02:12
upstream KASAN: use-after-free Read in ext4_find_extent ext4 19 2 1750d 1811d 0/29 auto-closed as invalid on 2022/02/17 05:19
android-6-1 KASAN: use-after-free Read in ext4_find_extent (2) origin:lts 19 syz, C 35 22d 431d 0/2 upstream: reported C repro on 2025/05/31 08:45
linux-6.1 KASAN: use-after-free Read in ext4_find_extent origin:upstream missing-backport 19 syz, C done 69 131d 1051d 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 syz, C error 142 2d03h 1318d 0/2 upstream: reported C repro on 2022/12/26 07:59
upstream KASAN: use-after-free Read in ext4_find_extent (4) prio:high ext4 19 syz, C done error 307 128d 582d 0/29 auto-obsoleted due to no activity on 2026/06/22 22:43
upstream KASAN: use-after-free Read in ext4_find_extent (3) prio:low ext4 19 syz, C error done 31 953d 1134d 25/29 fixed on 2024/01/30 23:26
android-54 KASAN: slab-out-of-bounds Read in ext4_find_extent ext4 17 syz, C 1 1132d 1318d 0/2 auto-obsoleted due to no activity on 2023/10/08 03:20
▶ ▼ Fix bisection attempts (3)
Created Duration User Patch Repo Result
2023/04/03 02:23 1h02m bisect fix upstream OK (0) job log log
2023/03/04 01:41 41m bisect fix upstream OK (0) job log log
2023/02/01 22:22 41m bisect fix upstream OK (0) job log log

Sample crash report:
loop0: detected capacity change from 0 to 2048
EXT4-fs (loop0): mounted filesystem 00000000-0000-0000-0000-000000000000 without journal. Quota mode: none.
==================================================================
BUG: KASAN: use-after-free in ext4_ext_binsearch_idx fs/ext4/extents.c:768 [inline]
BUG: KASAN: use-after-free in ext4_find_extent+0x76e/0xd90 fs/ext4/extents.c:931
Read of size 4 at addr ffff888073644750 by task syz-executor420/5067

CPU: 0 PID: 5067 Comm: syz-executor420 Not tainted 6.2.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1b1/0x290 lib/dump_stack.c:106
 print_address_description+0x74/0x340 mm/kasan/report.c:306
 print_report+0x107/0x1f0 mm/kasan/report.c:417
 kasan_report+0xcd/0x100 mm/kasan/report.c:517
 ext4_ext_binsearch_idx fs/ext4/extents.c:768 [inline]
 ext4_find_extent+0x76e/0xd90 fs/ext4/extents.c:931
 ext4_clu_mapped+0x117/0x970 fs/ext4/extents.c:5809
 ext4_insert_delayed_block fs/ext4/inode.c:1696 [inline]
 ext4_da_map_blocks fs/ext4/inode.c:1806 [inline]
 ext4_da_get_block_prep+0x9e8/0x13c0 fs/ext4/inode.c:1870
 ext4_block_write_begin+0x6a8/0x2290 fs/ext4/inode.c:1098
 ext4_da_write_begin+0x539/0x760 fs/ext4/inode.c:3082
 generic_perform_write+0x2e4/0x5e0 mm/filemap.c:3772
 ext4_buffered_write_iter+0x122/0x3a0 fs/ext4/file.c:285
 ext4_file_write_iter+0x1d0/0x18f0
 call_write_iter include/linux/fs.h:2186 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x7dc/0xc50 fs/read_write.c:584
 ksys_write+0x177/0x2a0 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f4b7a9737b9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 14 00 00 90 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 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc5cac3668 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f4b7a9737b9
RDX: 00000000175d9003 RSI: 0000000020000200 RDI: 0000000000000004
RBP: 00007f4b7a933050 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000079f R11: 0000000000000246 R12: 00007f4b7a9330e0
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

The buggy address belongs to the physical page:
page:ffffea0001cd9100 refcount:0 mapcount:0 mapping:0000000000000000 index:0x2 pfn:0x73644
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea0001cd9148 ffffea0001cd90c8 0000000000000000
raw: 0000000000000002 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 0x8(__GFP_MOVABLE), pid 1, tgid 1 (swapper/0), ts 12379768059, free_ts 13547634018
 split_map_pages+0x25b/0x540 mm/compaction.c:97
 isolate_freepages_range+0x4ac/0x510 mm/compaction.c:735
 alloc_contig_range+0x6a9/0x980 mm/page_alloc.c:9363
 __alloc_contig_pages mm/page_alloc.c:9386 [inline]
 alloc_contig_pages+0x3c8/0x4e0 mm/page_alloc.c:9463
 debug_vm_pgtable_alloc_huge_page+0xcd/0x120 mm/debug_vm_pgtable.c:1065
 init_args+0xa3a/0xdc0 mm/debug_vm_pgtable.c:1188
 debug_vm_pgtable+0x9a/0x4a0 mm/debug_vm_pgtable.c:1226
 do_one_initcall+0x1d1/0x410 init/main.c:1306
 do_initcall_level+0x168/0x220 init/main.c:1379
 do_initcalls+0x43/0x90 init/main.c:1395
 kernel_init_freeable+0x428/0x5e0 init/main.c:1634
 kernel_init+0x19/0x2b0 init/main.c:1522
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1446 [inline]
 free_pcp_prepare+0x751/0x780 mm/page_alloc.c:1496
 free_unref_page_prepare mm/page_alloc.c:3369 [inline]
 free_unref_page+0x19/0x4c0 mm/page_alloc.c:3464
 free_contig_range+0xa3/0x160 mm/page_alloc.c:9485
 destroy_args+0xfe/0x940 mm/debug_vm_pgtable.c:998
 debug_vm_pgtable+0x43d/0x4a0 mm/debug_vm_pgtable.c:1318
 do_one_initcall+0x1d1/0x410 init/main.c:1306
 do_initcall_level+0x168/0x220 init/main.c:1379
 do_initcalls+0x43/0x90 init/main.c:1395
 kernel_init_freeable+0x428/0x5e0 init/main.c:1634
 kernel_init+0x19/0x2b0 init/main.c:1522
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

Memory state around the buggy address:
 ffff888073644600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888073644680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888073644700: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                                 ^
 ffff888073644780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888073644800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2022/12/27 07:04 upstream 1b929c02afd3 9da18ae8 .config strace log report syz C [disk image] [vmlinux] [kernel image] [mounted in repro] ci2-upstream-fs KASAN: use-after-free Read in ext4_find_extent
2023/05/04 23:49 upstream 1a5304fecee5 518a39a6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs KASAN: use-after-free Read in ext4_find_extent
* Struck through repros no longer work on HEAD.