linux-kernel - Re: [syzbot] [batman?] KMSAN: uninit-value in skb

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Message-ID: <6925ee6a.a70a0220.2ea503.008e.GAE@google.com>
Date: Tue, 25 Nov 2025 09:59:06 -0800
From: syzbot <syzbot+2fa344348a579b779e05@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, ssranevjti@...il.com, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [batman?] KMSAN: uninit-value in skb_clone

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in skb_clone

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: 6008 Comm: syz.0.23 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 f3 28 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:ffffc9000d67f200 EFLAGS: 00010207
RAX: ffffffff89223591 RBX: 0000000000000000 RCX: ffff88803362c900
RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000000
RBP: 000000000000007e R08: ffffffff8f7d0f77 R09: 1ffffffff1efa1ee
R10: dffffc0000000000 R11: fffffbfff1efa1ef R12: dffffc0000000000
R13: 0000000000000820 R14: 000000000000000f R15: ffff888049098f00
FS:  00007f65d4fbc6c0(0000) GS:ffff88808d72f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f65d4fbbfc8 CR3: 0000000056473000 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:745
 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: 0033:0x7f65d598e1ff
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:00007f65d4fbc000 EFLAGS: 00000293 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f65d5be6180 RCX: 00007f65d598e1ff
RDX: 000000000000003e RSI: 0000200000000500 RDI: 00000000000000c8
RBP: 00007f65d4fbc090 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000003e R11: 0000000000000293 R12: 0000000000000001
R13: 00007f65d5be6218 R14: 00007f65d5be6180 R15: 00007ffeb6e64a58
 </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 f3 28 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:ffffc9000d67f200 EFLAGS: 00010207
RAX: ffffffff89223591 RBX: 0000000000000000 RCX: ffff88803362c900
RDX: 0000000000000000 RSI: 0000000000000820 RDI: 0000000000000000
RBP: 000000000000007e R08: ffffffff8f7d0f77 R09: 1ffffffff1efa1ee
R10: dffffc0000000000 R11: fffffbfff1efa1ef R12: dffffc0000000000
R13: 0000000000000820 R14: 000000000000000f R15: ffff888049098f00
FS:  00007f65d4fbc6c0(0000) GS:ffff88808d72f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f65d4fbbfc8 CR3: 0000000056473000 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 f3 28 05 f9       	call   0xf9052903
  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


Tested on:

commit:         30f09200 Merge tag 'arm64-fixes' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15e6cf42580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a1db0fea040c2a9f
dashboard link: https://syzkaller.appspot.com/bug?extid=2fa344348a579b779e05
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1281a612580000