general protection fault in netfs_prepare_write

Status: moderation: reported on 2026/08/07 10:04
Subsystems: netfs
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+d4c6ec1e452ec783f0d3@syzkaller.appspotmail.com
First crash: 7d06h, last: 1d10h
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
e70dcca3 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ✅ VMHostTrigger: ❌ ❓ general protection fault in netfs_prepare_write 2026/08/09 10:28 2026/08/09 10:28 2026/08/09 11:07 5d63f80b
ef6572da assessment-security 💥 general protection fault in netfs_prepare_write 2026/08/05 00:05 2026/08/05 00:05 2026/08/05 00:05 d4abbeac

Sample crash report:
RBP: 00007f6c82c24090 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007f6c82026038 R14: 00007f6c82025fa0 R15: 00007ffe5771d4c8
 </TASK>
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000015: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x00000000000000a8-0x00000000000000af]
CPU: 3 UID: 0 PID: 8019 Comm: syz.3.668 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:netfs_prepare_write+0xbc/0x7b0 fs/netfs/write_issue.c:173
Code: e1 07 38 ca 7f 08 84 d2 0f 85 04 06 00 00 48 8d bb ad 00 00 00 0f b6 45 52 48 ba 00 00 00 00 00 fc ff df 48 89 f9 48 c1 e9 03 <0f> b6 14 11 48 89 f9 83 e1 07 38 ca 7f 08 84 d2 0f 85 c1 05 00 00
RSP: 0018:ffffc90003437b40 EFLAGS: 00010203
RAX: 0000000000000005 RBX: 0000000000000000 RCX: 0000000000000015
RDX: dffffc0000000000 RSI: ffffffff82cb9199 RDI: 00000000000000ad
RBP: ffff88802421b1a0 R08: 00000000ffffffff R09: fffffbfff1dbdcfe
R10: ffffffff8edee7f3 R11: 0000000000000000 R12: ffff88802421b0c0
R13: ffff88802421b278 R14: 0000000000000000 R15: ffff88802421b1f2
FS:  00007f6c82c246c0(0000) GS:ffff8880d60ec000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000060841000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 netfs_unbuffered_write+0x75c/0x2020 fs/netfs/direct_write.c:111
 netfs_unbuffered_write_iter_locked+0x7d6/0xa80 fs/netfs/direct_write.c:290
 netfs_unbuffered_write_iter+0x442/0x720 fs/netfs/direct_write.c:382
 v9fs_file_write_iter+0xbf/0x100 fs/9p/vfs_file.c:409
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6ac/0x1050 fs/read_write.c:687
 ksys_write+0x12a/0x250 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6c81d9e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f6c82c24028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f6c82025fa0 RCX: 00007f6c81d9e0d9
RDX: 0000000000000012 RSI: 0000200000000000 RDI: 0000000000000003
RBP: 00007f6c82c24090 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007f6c82026038 R14: 00007f6c82025fa0 R15: 00007ffe5771d4c8
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:netfs_prepare_write+0xbc/0x7b0 fs/netfs/write_issue.c:173
Code: e1 07 38 ca 7f 08 84 d2 0f 85 04 06 00 00 48 8d bb ad 00 00 00 0f b6 45 52 48 ba 00 00 00 00 00 fc ff df 48 89 f9 48 c1 e9 03 <0f> b6 14 11 48 89 f9 83 e1 07 38 ca 7f 08 84 d2 0f 85 c1 05 00 00
RSP: 0018:ffffc90003437b40 EFLAGS: 00010203
RAX: 0000000000000005 RBX: 0000000000000000 RCX: 0000000000000015
RDX: dffffc0000000000 RSI: ffffffff82cb9199 RDI: 00000000000000ad
RBP: ffff88802421b1a0 R08: 00000000ffffffff R09: fffffbfff1dbdcfe
R10: ffffffff8edee7f3 R11: 0000000000000000 R12: ffff88802421b0c0
R13: ffff88802421b278 R14: 0000000000000000 R15: ffff88802421b1f2
FS:  00007f6c82c246c0(0000) GS:ffff8880d60ec000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055e4a6be8480 CR3: 0000000060841000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
   0:	e1 07                	loope  0x9
   2:	38 ca                	cmp    %cl,%dl
   4:	7f 08                	jg     0xe
   6:	84 d2                	test   %dl,%dl
   8:	0f 85 04 06 00 00    	jne    0x612
   e:	48 8d bb ad 00 00 00 	lea    0xad(%rbx),%rdi
  15:	0f b6 45 52          	movzbl 0x52(%rbp),%eax
  19:	48 ba 00 00 00 00 00 	movabs $0xdffffc0000000000,%rdx
  20:	fc ff df
  23:	48 89 f9             	mov    %rdi,%rcx
  26:	48 c1 e9 03          	shr    $0x3,%rcx
* 2a:	0f b6 14 11          	movzbl (%rcx,%rdx,1),%edx <-- trapping instruction
  2e:	48 89 f9             	mov    %rdi,%rcx
  31:	83 e1 07             	and    $0x7,%ecx
  34:	38 ca                	cmp    %cl,%dl
  36:	7f 08                	jg     0x40
  38:	84 d2                	test   %dl,%dl
  3a:	0f 85 c1 05 00 00    	jne    0x601

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/09 05:49 upstream 06cf61899d64 5d63f80b .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream general protection fault in netfs_prepare_write
2026/08/03 10:01 upstream 075b74841bd0 e611ffe1 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream general protection fault in netfs_prepare_write
* Struck through repros no longer work on HEAD.