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BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write

Status: upstream: reported C repro on 2026/03/06 06:36
Subsystems: netfs
[Documentation on labels]
Reported-by: syzbot+7227db0fbac9f348dba0@syzkaller.appspotmail.com
Fix commit: netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry
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: 8d21h, last: 12m
▶ ▼ Discussions (3)
Title Replies (including bot) Last reply
[PATCH] netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry 2 (2) 2026/03/09 09:22
[syzbot] [netfs?] kernel BUG in netfs_limit_iter 2 (6) 2026/03/07 14:12
[syzbot] [netfs?] BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write 1 (7) 2026/03/07 08:00
▶ ▼ Last patch testing requests (5)
Created Duration User Patch Repo Result
2026/03/07 07:27 19m dhowells@redhat.com patch git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git c107785c7e8d OK log
2026/03/07 03:58 20m kartikey406@gmail.com patch upstream OK log
2026/03/07 01:06 13m kartikey406@gmail.com patch upstream error
2026/03/07 00:41 12m kartikey406@gmail.com patch upstream error
2026/03/07 00:12 12m kartikey406@gmail.com patch upstream error

Sample crash report:
netfs: Couldn't get user pages (rc=-14)
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 31867067 P4D 31867067 PUD 0 
Oops: Oops: 0010 [#1] SMP KASAN NOPTI
CPU: 3 UID: 0 PID: 6079 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffc90003b7fb90 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88803bd3a5b0 RCX: ffffffff82c49d0a
RDX: ffff88802b9ca4c0 RSI: ffffffff82c49b9c RDI: ffff88803bd3a500
RBP: 0000000000140000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88803bd3a598
R13: dffffc0000000000 R14: ffff88803bd3a500 R15: ffff888023066580
FS:  00007f9e9a09f6c0(0000) GS:ffff8880d6644000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000002c65b000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 netfs_unbuffered_write+0xae5/0x2080 fs/netfs/direct_write.c:189
 netfs_unbuffered_write_iter_locked+0x801/0xab0 fs/netfs/direct_write.c:287
 netfs_unbuffered_write_iter+0x40c/0x710 fs/netfs/direct_write.c:377
 v9fs_file_write_iter+0xbf/0x100 fs/9p/vfs_file.c:409
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x6ac/0x1070 fs/read_write.c:688
 ksys_write+0x12a/0x250 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9e9919c799
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:00007f9e9a09f028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f9e99415fa0 RCX: 00007f9e9919c799
RDX: 000000000208e24b RSI: 0000200000000000 RDI: 0000000000000003
RBP: 00007f9e99232bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9e99416038 R14: 00007f9e99415fa0 R15: 00007fff05034208
 </TASK>
Modules linked in:
CR2: 0000000000000000
---[ end trace 0000000000000000 ]---
RIP: 0010:0x0
Code: Unable to access opcode bytes at 0xffffffffffffffd6.
RSP: 0018:ffffc90003b7fb90 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88803bd3a5b0 RCX: ffffffff82c49d0a
RDX: ffff88802b9ca4c0 RSI: ffffffff82c49b9c RDI: ffff88803bd3a500
RBP: 0000000000140000 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88803bd3a598
R13: dffffc0000000000 R14: ffff88803bd3a500 R15: ffff888023066580
FS:  00007f9e9a09f6c0(0000) GS:ffff8880d6644000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000002c65b000 CR4: 0000000000352ef0

Crashes (125):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/05 19:17 upstream c107785c7e8d d20b04c8 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/05 18:38 upstream c107785c7e8d d20b04c8 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/05 17:57 upstream c107785c7e8d d20b04c8 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/14 12:53 upstream 1c9982b49613 ee8d34d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/14 02:38 upstream 1c9982b49613 ee8d34d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/13 23:24 upstream b36eb6e3f5d8 351cb5cf .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/13 21:57 upstream b36eb6e3f5d8 351cb5cf .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/13 21:54 upstream b36eb6e3f5d8 351cb5cf .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/13 20:31 upstream b36eb6e3f5d8 351cb5cf .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/13 15:52 upstream 0257f64bdac7 351cb5cf .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/13 13:07 upstream 0257f64bdac7 2f7f359d .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/13 05:13 upstream 0257f64bdac7 2f7f359d .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/13 01:06 upstream 0257f64bdac7 2f7f359d .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/12 19:49 upstream 80234b5ab240 4efadf07 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/12 14:20 upstream 80234b5ab240 4efadf07 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/12 04:19 upstream 80234b5ab240 2d88ab01 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/11 23:38 upstream b29fb8829bff 2d88ab01 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/11 21:43 upstream b29fb8829bff 2d88ab01 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/11 19:07 upstream b29fb8829bff 2d88ab01 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/11 17:55 upstream b29fb8829bff 2d88ab01 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/11 15:54 upstream b29fb8829bff 2d88ab01 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/11 05:23 upstream b4f0dd314b39 86914af9 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/11 00:53 upstream b4f0dd314b39 4683d576 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/10 23:46 upstream b4f0dd314b39 4683d576 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/10 23:41 upstream b4f0dd314b39 4683d576 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/10 23:40 upstream b4f0dd314b39 4683d576 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/10 18:38 upstream 1f318b96cc84 4683d576 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/10 14:08 upstream 1f318b96cc84 4683d576 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/10 07:23 upstream 1f318b96cc84 6972f302 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/10 00:33 upstream 1f318b96cc84 176bead5 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/09 19:44 upstream 1f318b96cc84 176bead5 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/09 11:36 upstream 014441d1e4b2 5cb44a80 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/09 07:14 upstream 014441d1e4b2 5cb44a80 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/09 05:49 upstream 014441d1e4b2 5cb44a80 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/09 01:30 upstream 014441d1e4b2 5cb44a80 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/08 22:16 upstream c23719abc330 5cb44a80 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/14 14:22 upstream 1c9982b49613 ee8d34d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/14 11:47 upstream 1c9982b49613 ee8d34d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/14 11:32 upstream 1c9982b49613 ee8d34d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/14 11:08 upstream 1c9982b49613 ee8d34d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/14 11:06 upstream 1c9982b49613 ee8d34d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/14 08:41 upstream 1c9982b49613 ee8d34d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/14 05:38 upstream 1c9982b49613 ee8d34d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/14 03:49 upstream 1c9982b49613 ee8d34d6 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/13 14:42 upstream 0257f64bdac7 351cb5cf .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/12 03:15 upstream b29fb8829bff 2d88ab01 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/10 20:00 upstream 1f318b96cc84 4683d576 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
2026/03/10 10:10 upstream 1f318b96cc84 6972f302 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 BUG: unable to handle kernel NULL pointer dereference in netfs_unbuffered_write
* Struck through repros no longer work on HEAD.