syzbot


KMSAN: uninit-value in skb_clone

Status: upstream: reported C repro on 2025/11/25 16:32
Subsystems: batman
[Documentation on labels]
Reported-by: syzbot+2fa344348a579b779e05@syzkaller.appspotmail.com
Fix commit: net/hsr: fix NULL pointer dereference in prp_get_untagged_frame()
Patched on: [ci-upstream-linux-next-kasan-gce-root ci-upstream-net-this-kasan-gce 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 ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb]
First crash: 22d, last: 21d
Discussions (4)
Title Replies (including bot) Last reply
[PATCH net v3] net/hsr: fix NULL pointer dereference in prp_get_untagged_frame() 4 (4) 2025/12/04 10:20
[PATCH net v2] net/hsr: fix NULL pointer dereference in skb_clone with hw tag insertion 3 (3) 2025/11/29 16:29
[syzbot] [batman?] KMSAN: uninit-value in skb_clone 3 (7) 2025/11/29 16:23
[PATCH] hsr: fix NULL pointer dereference in skb_clone with hw tag insertion 3 (3) 2025/11/27 15:20
Similar bugs (8)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.14 general protection fault in skb_clone 2 C 1 1021d 1154d 0/1 upstream: reported C repro on 2022/10/17 02:33
upstream BUG: unable to handle kernel paging request in skb_clone net 8 2 1584d 1628d 0/29 closed as invalid on 2021/10/04 21:36
linux-4.19 general protection fault in skb_clone 2 C error 2 1154d 1463d 0/1 upstream: reported C repro on 2021/12/12 07:38
upstream general protection fault in skb_clone (4) net 10 C unreliable 41 1166d 1463d 0/29 closed as invalid on 2022/10/12 18:15
upstream general protection fault in skb_clone (5) net 10 C done 7 1139d 1157d 22/29 fixed on 2023/02/24 13:50
upstream general protection fault in skb_clone 2 syz 3 3042d 3041d 3/29 fixed on 2017/10/24 19:00
upstream general protection fault in skb_clone (3) net 2 44 2026d 2028d 15/29 fixed on 2020/07/17 17:58
upstream general protection fault in skb_clone (2) hams 2 1 2210d 2207d 0/29 auto-closed as invalid on 2020/03/25 12:28
Last patch testing requests (3)
Created Duration User Patch Repo Result
2025/11/29 16:01 20m ssranevjti@gmail.com patch upstream OK log
2025/11/25 20:03 20m ssranevjti@gmail.com patch upstream OK log
2025/11/25 17:42 16m ssranevjti@gmail.com patch upstream report log

Sample crash report:
syz_tun: entered promiscuous mode
bond0: (slave syz_tun): Enslaving as an active interface with an up link
Oops: general protection fault, probably for non-canonical address 0xdffffc000000000f: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000078-0x000000000000007f]
CPU: 0 UID: 0 PID: 5625 Comm: syz.1.18 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:skb_clone+0xd7/0x3a0 net/core/skbuff.c:2041
Code: 03 42 80 3c 20 00 74 08 4c 89 f7 e8 23 29 05 f9 49 83 3e 00 0f 85 a0 01 00 00 e8 94 dd 9d f8 48 8d 6b 7e 49 89 ee 49 c1 ee 03 <43> 0f b6 04 26 84 c0 0f 85 d1 01 00 00 44 0f b6 7d 00 41 83 e7 0c
RSP: 0018:ffffc9000d00f200 EFLAGS: 00010207
RAX: ffffffff892235a1 RBX: 0000000000000000 RCX: ffff88803372a480
RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000000
RBP: 000000000000007e R08: ffffffff8f7d0f77 R09: 1ffffffff1efa1ee
R10: dffffc0000000000 R11: fffffbfff1efa1ef R12: dffffc0000000000
R13: 0000000000000820 R14: 000000000000000f R15: ffff88805144cc00
FS:  0000555557f6d500(0000) GS:ffff88808d72f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555581d35808 CR3: 000000005040e000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 hsr_forward_do net/hsr/hsr_forward.c:-1 [inline]
 hsr_forward_skb+0x1013/0x2860 net/hsr/hsr_forward.c:741
 hsr_handle_frame+0x6ce/0xa70 net/hsr/hsr_slave.c:84
 __netif_receive_skb_core+0x10b9/0x4380 net/core/dev.c:5966
 __netif_receive_skb_one_core net/core/dev.c:6077 [inline]
 __netif_receive_skb+0x72/0x380 net/core/dev.c:6192
 netif_receive_skb_internal net/core/dev.c:6278 [inline]
 netif_receive_skb+0x1cb/0x790 net/core/dev.c:6337
 tun_rx_batched+0x1b9/0x730 drivers/net/tun.c:1485
 tun_get_user+0x2b65/0x3e90 drivers/net/tun.c:1953
 tun_chr_write_iter+0x113/0x200 drivers/net/tun.c:1999
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x5c9/0xb30 fs/read_write.c:686
 ksys_write+0x145/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0449f8e1ff
Code: 89 54 24 18 48 89 74 24 10 89 7c 24 08 e8 f9 92 02 00 48 8b 54 24 18 48 8b 74 24 10 41 89 c0 8b 7c 24 08 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 31 44 89 c7 48 89 44 24 08 e8 4c 93 02 00 48
RSP: 002b:00007ffd7ad94c90 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f044a1e5fa0 RCX: 00007f0449f8e1ff
RDX: 000000000000003e RSI: 0000200000000500 RDI: 00000000000000c8
RBP: 00007ffd7ad94d20 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000003e R11: 0000000000000293 R12: 0000000000000001
R13: 00007f044a1e5fa0 R14: 00007f044a1e5fa0 R15: 0000000000000003
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:skb_clone+0xd7/0x3a0 net/core/skbuff.c:2041
Code: 03 42 80 3c 20 00 74 08 4c 89 f7 e8 23 29 05 f9 49 83 3e 00 0f 85 a0 01 00 00 e8 94 dd 9d f8 48 8d 6b 7e 49 89 ee 49 c1 ee 03 <43> 0f b6 04 26 84 c0 0f 85 d1 01 00 00 44 0f b6 7d 00 41 83 e7 0c
RSP: 0018:ffffc9000d00f200 EFLAGS: 00010207
RAX: ffffffff892235a1 RBX: 0000000000000000 RCX: ffff88803372a480
RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000000
RBP: 000000000000007e R08: ffffffff8f7d0f77 R09: 1ffffffff1efa1ee
R10: dffffc0000000000 R11: fffffbfff1efa1ef R12: dffffc0000000000
R13: 0000000000000820 R14: 000000000000000f R15: ffff88805144cc00
FS:  0000555557f6d500(0000) GS:ffff88808d72f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555581d35808 CR3: 000000005040e000 CR4: 0000000000352ef0
----------------
Code disassembly (best guess):
   0:	03 42 80             	add    -0x80(%rdx),%eax
   3:	3c 20                	cmp    $0x20,%al
   5:	00 74 08 4c          	add    %dh,0x4c(%rax,%rcx,1)
   9:	89 f7                	mov    %esi,%edi
   b:	e8 23 29 05 f9       	call   0xf9052933
  10:	49 83 3e 00          	cmpq   $0x0,(%r14)
  14:	0f 85 a0 01 00 00    	jne    0x1ba
  1a:	e8 94 dd 9d f8       	call   0xf89dddb3
  1f:	48 8d 6b 7e          	lea    0x7e(%rbx),%rbp
  23:	49 89 ee             	mov    %rbp,%r14
  26:	49 c1 ee 03          	shr    $0x3,%r14
* 2a:	43 0f b6 04 26       	movzbl (%r14,%r12,1),%eax <-- trapping instruction
  2f:	84 c0                	test   %al,%al
  31:	0f 85 d1 01 00 00    	jne    0x208
  37:	44 0f b6 7d 00       	movzbl 0x0(%rbp),%r15d
  3c:	41 83 e7 0c          	and    $0xc,%r15d

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/23 15:01 upstream d13f3ac64efb 4fb8ef37 .config console log report syz / log C [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root general protection fault in skb_clone
2025/11/21 16:27 upstream fd95357fd8c6 c31c1b0b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kmsan-gce-386-root KMSAN: uninit-value in skb_clone
2025/11/23 14:12 upstream d13f3ac64efb 4fb8ef37 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root general protection fault in skb_clone
* Struck through repros no longer work on HEAD.