syzbot


KMSAN: uninit-value in xlog_verify_head

Status: upstream: reported on 2026/04/02 18:55
Subsystems: xfs
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+b7dfbed0c6c2b5e9fd34@syzkaller.appspotmail.com
Fix commit: cc9af5e461ea xfs: use null daddr for unset first bad log block
Patched on: [ci-qemu-gce-upstream-auto ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-snapshot-upstream-root 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-linux-next-kasan-gce-root ci-upstream-rust-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce], missing on: [ci-qemu-native-arm64-kvm ci-qemu2-riscv64 ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci2-upstream-usb]
First crash: 97d, last: 97d
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
54e54d68-fb87-42e2-983c-d1ec2e9b8dce assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ✅ NetworkTrigger: ❌ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ KMSAN: uninit-value in xlog_verify_head 2026/05/30 21:38 2026/05/30 21:38 2026/05/30 22:36 6b4a844333e83556da95d61d7f207e7ef5cd4bc6

			
		
8d464bff-5cf4-4ca1-9c41-284d40a140fc assessment-security 💥 KMSAN: uninit-value in xlog_verify_head 2026/05/14 11:54 2026/05/14 11:54 2026/05/14 11:56 6ccb967e465e832a7bfd7a116ad00d52a0923a5d
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/09d1caa061cb53c83a...
truncated to first 200 bytes; open job for full error
Discussions (4)
Title Replies (including bot) Last reply
[PATCH v2] xfs: use null daddr for unset first bad log block 4 (4) 2026/07/01 12:50
[PATCH] xfs: initialize first bad log block in head verification 3 (3) 2026/06/30 10:01
[PATCH] xfs: reject CRC validation when the log header cannot be retrieved 4 (4) 2026/04/07 07:47
[syzbot] [xfs?] KMSAN: uninit-value in xlog_verify_head 0 (1) 2026/04/02 18:55

Sample crash report:
XFS (loop4): Mounting V5 Filesystem d7dc424e-7990-42cb-9f91-9cb7200a101d
=====================================================
BUG: KMSAN: uninit-value in xlog_verify_head+0x6c3/0x910 fs/xfs/xfs_log_recover.c:1058
 xlog_verify_head+0x6c3/0x910 fs/xfs/xfs_log_recover.c:1058
 xlog_find_tail+0xc2e/0x1a50 fs/xfs/xfs_log_recover.c:1315
 xlog_recover+0x6d/0x800 fs/xfs/xfs_log_recover.c:3426
 xfs_log_mount+0x4da/0x880 fs/xfs/xfs_log.c:617
 xfs_mountfs+0x1599/0x2d00 fs/xfs/xfs_mount.c:1034
 xfs_fs_fill_super+0x2603/0x2be0 fs/xfs/xfs_super.c:1938
 get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
 get_tree_bdev+0x38/0x50 fs/super.c:1717
 xfs_fs_get_tree+0x35/0x40 fs/xfs/xfs_super.c:1985
 vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3763 [inline]
 do_new_mount+0x885/0x1dd0 fs/namespace.c:3839
 path_mount+0x7a2/0x20b0 fs/namespace.c:4159
 do_mount fs/namespace.c:4172 [inline]
 __do_sys_mount fs/namespace.c:4361 [inline]
 __se_sys_mount+0x704/0x7f0 fs/namespace.c:4338
 __ia32_sys_mount+0xe2/0x150 fs/namespace.c:4338
 ia32_sys_call+0x27fe/0x4360 arch/x86/include/generated/asm/syscalls_32.h:22
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x17f/0x3f0 arch/x86/entry/syscall_32.c:307
 do_fast_syscall_32+0x37/0x80 arch/x86/entry/syscall_32.c:332
 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:370
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e

Uninit was stored to memory at:
 xlog_verify_head+0x6bc/0x910 fs/xfs/xfs_log_recover.c:1058
 xlog_find_tail+0xc2e/0x1a50 fs/xfs/xfs_log_recover.c:1315
 xlog_recover+0x6d/0x800 fs/xfs/xfs_log_recover.c:3426
 xfs_log_mount+0x4da/0x880 fs/xfs/xfs_log.c:617
 xfs_mountfs+0x1599/0x2d00 fs/xfs/xfs_mount.c:1034
 xfs_fs_fill_super+0x2603/0x2be0 fs/xfs/xfs_super.c:1938
 get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
 get_tree_bdev+0x38/0x50 fs/super.c:1717
 xfs_fs_get_tree+0x35/0x40 fs/xfs/xfs_super.c:1985
 vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3763 [inline]
 do_new_mount+0x885/0x1dd0 fs/namespace.c:3839
 path_mount+0x7a2/0x20b0 fs/namespace.c:4159
 do_mount fs/namespace.c:4172 [inline]
 __do_sys_mount fs/namespace.c:4361 [inline]
 __se_sys_mount+0x704/0x7f0 fs/namespace.c:4338
 __ia32_sys_mount+0xe2/0x150 fs/namespace.c:4338
 ia32_sys_call+0x27fe/0x4360 arch/x86/include/generated/asm/syscalls_32.h:22
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x17f/0x3f0 arch/x86/entry/syscall_32.c:307
 do_fast_syscall_32+0x37/0x80 arch/x86/entry/syscall_32.c:332
 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:370
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e

Local variable tmp_rhead_blk created at:
 xlog_verify_head+0x81/0x910 fs/xfs/xfs_log_recover.c:1032
 xlog_find_tail+0xc2e/0x1a50 fs/xfs/xfs_log_recover.c:1315

CPU: 1 UID: 0 PID: 7664 Comm: syz.4.285 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
=====================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/29 18:48 upstream cbfffcca2bf0 356bdfc9 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-386-root KMSAN: uninit-value in xlog_verify_head
* Struck through repros no longer work on HEAD.