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KASAN: use-after-free Read in check_dirent

Status: upstream: reported C repro on 2025/02/21 16:28
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+87078ad27cd8af3263cc@syzkaller.appspotmail.com
Fix commit: bcachefs: Fix UAF in check_dirent()
Patched on: [ci-upstream-linux-next-kasan-gce-root ci-upstream-rust-kasan-gce], missing on: [ci-qemu-gce-upstream-auto ci-qemu-native-arm64-kvm ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb]
First crash: 484d, last: 302d
Cause bisection: introduced by (bisect log) :
commit cf3da2d627037a0848e25dbaeaedfadfe534c7c4
Author: Kent Overstreet <kent.overstreet@linux.dev>
Date: Mon Dec 16 18:58:02 2024 +0000

  bcachefs: Handle -BCH_ERR_need_mark_replicas in gc

Crash: KASAN: use-after-free Read in bch2_check_dirents (log)
Repro: C syz .config
  
▶ ▼ ✨ AI Jobs (5)
ID Workflow Result Correct Bug Created Started Finished Revision Error
51bb1da8-fead-41d6-b5ee-e91e37412ba1 assessment-security 💥 KASAN: use-after-free Read in check_dirent 2026/06/18 00:38 2026/06/18 00:38 2026/06/18 01:11 b62b3ded1759f79b37600c5ffe2b0a81b919b0b0 
failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/b5449abc758e00f3e0...
truncated to first 200 bytes; open job for full error
6904e84f-ba5b-4139-b459-82abee1e14b7 assessment-security 💥 KASAN: use-after-free Read in check_dirent 2026/06/09 20:30 2026/06/09 20:30 2026/06/09 20:57 c36c07f6c1f2230a36374cbd22235f635e8f9284 
failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/b5449abc758e00f3e0...
truncated to first 200 bytes; open job for full error
b9a1648f-f428-4985-a93e-72c8db63a12e assessment-security 💥 KASAN: use-after-free Read in check_dirent 2026/06/02 20:43 2026/06/02 20:43 2026/06/02 21:17 62fe15281f5011cd203d8845b8767b10e7443aa5 
failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/b5449abc758e00f3e0...
truncated to first 200 bytes; open job for full error
1717c469-6dd4-4a2e-b92f-6dca44bf1e07 assessment-security 💥 KASAN: use-after-free Read in check_dirent 2026/05/30 13:24 2026/05/30 13:24 2026/05/30 13:59 6b4a844333e83556da95d61d7f207e7ef5cd4bc6 
failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/b5449abc758e00f3e0...
truncated to first 200 bytes; open job for full error
02d94297-f8b1-4b9e-a423-bdd4a0168260 assessment-security 💥 KASAN: use-after-free Read in check_dirent 2026/05/14 10:29 2026/05/14 10:29 2026/05/14 10:30 6ccb967e465e832a7bfd7a116ad00d52a0923a5d 
failed to run ["git" "pull" "origin" "HEAD" "--depth=1" "--allow-unrelated-histories"]: exit status 128
From /app/workdir/repo/linux
 * branch                HEAD       -> FETCH_HEAD
Updating files:  ...
truncated to first 200 bytes; open job for full error
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [bcachefs?] KASAN: use-after-free Read in check_dirent 1 (3) 2025/07/19 19:19
▶ ▼ Last patch testing requests (3)
Created Duration User Patch Repo Result
2025/05/29 21:35 29m retest repro upstream report log
2025/03/11 16:06 26m retest repro upstream report log
2025/03/11 16:06 23m retest repro upstream report log
▶ ▼ Fix bisection attempts (3)
Created Duration User Patch Repo Result
2025/07/16 19:17 2h18m bisect fix upstream OK (0) job log log
2025/06/15 17:26 5h01m bisect fix upstream OK (0) job log log
2025/05/15 17:13 3h28m bisect fix upstream OK (0) job log log

Sample crash report:
bcachefs (loop4): check_extents... done
bcachefs (loop4): check_dirents...
dirent points to missing inode:
u64s 8 type dirent 4096:6728544935518790663:U32_MAX len 0 ver 0: lost+found -> 4097 type dir, fixing
==================================================================
BUG: KASAN: use-after-free in check_dirent+0x2455/0x2620 fs/bcachefs/fsck.c:2443
Read of size 1 at addr ffff888066404048 by task syz-executor384/5844

CPU: 1 UID: 0 PID: 5844 Comm: syz-executor384 Not tainted 6.14.0-rc3-syzkaller-00137-g27eddbf34490 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0xc3/0x670 mm/kasan/report.c:521
 kasan_report+0xd9/0x110 mm/kasan/report.c:634
 check_dirent+0x2455/0x2620 fs/bcachefs/fsck.c:2443
 bch2_check_dirents+0x409/0x780 fs/bcachefs/fsck.c:2468
 bch2_run_recovery_pass+0x91/0x1a0 fs/bcachefs/recovery_passes.c:226
 bch2_run_recovery_passes+0x3f4/0x8f0 fs/bcachefs/recovery_passes.c:291
 bch2_fs_recovery+0x3c1b/0x43d0 fs/bcachefs/recovery.c:973
 bch2_fs_start+0x343/0x660 fs/bcachefs/super.c:1041
 bch2_fs_get_tree+0x1118/0x1760 fs/bcachefs/fs.c:2203
 vfs_get_tree+0x8e/0x340 fs/super.c:1814
 do_new_mount fs/namespace.c:3560 [inline]
 path_mount+0x14e6/0x1f10 fs/namespace.c:3887
 do_mount fs/namespace.c:3900 [inline]
 __do_sys_mount fs/namespace.c:4111 [inline]
 __se_sys_mount fs/namespace.c:4088 [inline]
 __x64_sys_mount+0x28f/0x310 fs/namespace.c:4088
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f54eae1a3ea
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 5e 04 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 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:00007ffda345d9a8 EFLAGS: 00000282 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ffda345d9c0 RCX: 00007f54eae1a3ea
RDX: 0000400000000000 RSI: 0000400000000040 RDI: 00007ffda345d9c0
RBP: 0000400000000000 R08: 00007ffda345da00 R09: 0000000000005956
R10: 0000000001000001 R11: 0000000000000282 R12: 0000400000000040
R13: 0000000000000004 R14: 0000000000000003 R15: 00007ffda345da00
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x66404
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 0000000000000000 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 5, migratetype Unmovable, gfp_mask 0x52800(GFP_NOWAIT|__GFP_NORETRY|__GFP_COMP), pid 5844, tgid 5844 (syz-executor384), ts 93104285109, free_ts 93483581928
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x181/0x1b0 mm/page_alloc.c:1551
 prep_new_page mm/page_alloc.c:1559 [inline]
 get_page_from_freelist+0xfce/0x2f80 mm/page_alloc.c:3477
 __alloc_frozen_pages_noprof+0x221/0x2470 mm/page_alloc.c:4739
 __alloc_pages_noprof+0xb/0x1b0 mm/page_alloc.c:4773
 __alloc_pages_node_noprof include/linux/gfp.h:265 [inline]
 alloc_pages_node_noprof include/linux/gfp.h:292 [inline]
 ___kmalloc_large_node+0x84/0x1b0 mm/slub.c:4239
 __kmalloc_large_node_noprof+0x1c/0x70 mm/slub.c:4266
 __do_kmalloc_node mm/slub.c:4282 [inline]
 __kmalloc_node_noprof.cold+0x5/0x5f mm/slub.c:4300
 __kvmalloc_node_noprof+0x6f/0x1a0 mm/util.c:662
 btree_bounce_alloc+0x11e/0x210 fs/bcachefs/btree_io.c:123
 btree_node_sort+0x1104/0x14f0 fs/bcachefs/btree_io.c:322
 bch2_btree_post_write_cleanup fs/bcachefs/btree_io.c:2293 [inline]
 bch2_btree_post_write_cleanup+0x145/0x600 fs/bcachefs/btree_io.c:2267
 bch2_btree_node_prep_for_write+0x35b/0x550 fs/bcachefs/btree_trans_commit.c:93
 bch2_trans_lock_write+0x6c5/0x8e0 fs/bcachefs/btree_trans_commit.c:129
 do_bch2_trans_commit fs/bcachefs/btree_trans_commit.c:862 [inline]
 __bch2_trans_commit+0x2264/0x7d70 fs/bcachefs/btree_trans_commit.c:1070
 bch2_trans_commit fs/bcachefs/btree_update.h:183 [inline]
 __bch2_str_hash_check_key+0x2097/0x3800 fs/bcachefs/str_hash.c:292
 bch2_str_hash_check_key fs/bcachefs/str_hash.h:415 [inline]
 check_dirent+0x12d3/0x2620 fs/bcachefs/fsck.c:2373
page last free pid 5844 tgid 5844 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1127 [inline]
 __free_pages_ok+0x62b/0xe50 mm/page_alloc.c:1271
 __folio_put+0x32a/0x450 mm/swap.c:112
 kvfree+0x47/0x50 mm/util.c:705
 btree_bounce_free fs/bcachefs/btree_io.c:111 [inline]
 btree_node_sort+0xf9f/0x14f0 fs/bcachefs/btree_io.c:379
 bch2_btree_post_write_cleanup fs/bcachefs/btree_io.c:2293 [inline]
 bch2_btree_post_write_cleanup+0x145/0x600 fs/bcachefs/btree_io.c:2267
 bch2_btree_node_prep_for_write+0x35b/0x550 fs/bcachefs/btree_trans_commit.c:93
 bch2_trans_lock_write+0x6c5/0x8e0 fs/bcachefs/btree_trans_commit.c:129
 do_bch2_trans_commit fs/bcachefs/btree_trans_commit.c:862 [inline]
 __bch2_trans_commit+0x2264/0x7d70 fs/bcachefs/btree_trans_commit.c:1070
 bch2_trans_commit fs/bcachefs/btree_update.h:183 [inline]
 check_dirent+0xff1/0x2620 fs/bcachefs/fsck.c:2438
 bch2_check_dirents+0x409/0x780 fs/bcachefs/fsck.c:2468
 bch2_run_recovery_pass+0x91/0x1a0 fs/bcachefs/recovery_passes.c:226
 bch2_run_recovery_passes+0x3f4/0x8f0 fs/bcachefs/recovery_passes.c:291
 bch2_fs_recovery+0x3c1b/0x43d0 fs/bcachefs/recovery.c:973
 bch2_fs_start+0x343/0x660 fs/bcachefs/super.c:1041
 bch2_fs_get_tree+0x1118/0x1760 fs/bcachefs/fs.c:2203
 vfs_get_tree+0x8e/0x340 fs/super.c:1814

Memory state around the buggy address:
 ffff888066403f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888066403f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888066404000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff888066404080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888066404100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================
directory 4096:4294967295 with wrong i_size: got 288, should be 352, fixing
 done
bcachefs (loop4): resume_logged_ops... done
bcachefs (loop4): delete_dead_inodes... done
bcachefs (loop4): Second fsck run was not clean
bcachefs (loop4): going read-only
bcachefs (loop4): finished waiting for writes to stop
bcachefs (loop4): flushing journal and stopping allocators, journal seq 23
bcachefs (loop4): flushing journal and stopping allocators complete, journal seq 24
bcachefs (loop4): clean shutdown complete, journal seq 25
bcachefs (loop4): marking filesystem clean
bcachefs (loop4): done starting filesystem
syz-executor384 (5844) used greatest stack depth: 15712 bytes left

Crashes (13):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/02/21 16:58 upstream 27eddbf34490 0808a665 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/02/21 12:25 upstream 27eddbf34490 0808a665 .config strace log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/08/22 08:26 upstream 3957a5720157 bf27483f .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/08/17 00:10 upstream 90d970cade8e 1804e95e .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/07/31 04:54 upstream e8d780dcd957 f8f2b4da .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/04/10 09:57 upstream 3b07108ada81 988b336c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/03/28 04:18 upstream 1a9239bb4253 6c09fb82 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/03/26 05:10 upstream 2df0c02dab82 89d30d73 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/03/20 05:45 upstream a7f2e10ecd8f 3b7445cf .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/02/25 13:38 upstream d082ecbc71e9 d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/02/25 13:31 upstream d082ecbc71e9 d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/02/21 02:22 upstream 27eddbf34490 0808a665 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
2025/02/21 02:22 upstream 27eddbf34490 0808a665 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: use-after-free Read in check_dirent
* Struck through repros no longer work on HEAD.