[syzbot] [net?] BUG: unable to handle kernel paging request in nsim_drv_port_add (2)

[syzbot] [net?] BUG: unable to handle kernel paging request in nsim_drv_port_add (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    36aad21d50d1 Merge tag 'ksmbd-for-7.4-rc1-part2' of git://..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1332b159580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=dc4462df6d1062fe
dashboard link: https://syzkaller.appspot.com/bug?extid=b3fca27eb4005f0111f4
compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1194b795580000

AI-generated root cause summary:
In netdevsim, sysfs device attributes such as 'new_port' and 'del_port' are
exposed at the device level on nsim_bus_dev without holding device_lock or
checking if the driver is bound. An access via sysfs after the driver has been
unbound, after a failed probe, or concurrently with device removal finds drvdata
set to NULL; passing this NULL pointer to priv_to_devlink() computes a negative
offset from NULL, triggering a kernel page fault crash when attempting to
acquire devlink->lock.

full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=b3fca27eb4005f0111f4

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b3fca27eb4005f0111f4@syzkaller.appspotmail.com

BUG: unable to handle page fault for address: fffffffffffffeb0
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD f1b3067 P4D f1b3067 PUD f1b5067 PMD 0 
Oops: Oops: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 6031 Comm: syz-executor405 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/15/2026
RIP: 0010:__lock_acquire+0x41/0x2de0 kernel/locking/lockdep.c:5140
Code: 2d 12 48 89 84 24 e0 00 00 00 65 48 8b 05 0f e3 2d 12 48 89 44 24 08 45 31 f6 83 3d 28 dc 32 0f 00 0f 84 90 14 00 00 48 89 fb <48> 8b 07 48 3d a0 69 92 94 0f 84 7e 14 00 00 45 89 cd 89 cd 41 89
RSP: 0018:ffffc900046978d8 EFLAGS: 00010002
RAX: ffff88801ff11f40 RBX: fffffffffffffeb0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: fffffffffffffeb0
RBP: ffff88801ff11f40 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000100 R11: 0000000000000007 R12: fffffffffffffeb0
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000246
FS:  000055558a5ef400(0000) GS:ffff888124716000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffffffffeb0 CR3: 00000000452a0000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 __mutex_lock_common kernel/locking/rtmutex_api.c:561 [inline]
 mutex_lock_nested+0x55/0x1d0 kernel/locking/rtmutex_api.c:580
 nsim_drv_port_add+0x5a/0x140 drivers/net/netdevsim/dev.c:1760
 new_port_store+0x1a5/0x280 drivers/net/netdevsim/bus.c:96
 kernfs_fop_write_iter+0x3a5/0x540 fs/kernfs/file.c:345
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x61e/0xbb0 fs/read_write.c:687
 ksys_write+0x156/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efc00506777
Code: 48 89 fa 4c 89 df e8 58 1c 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007fff1f51a010 EFLAGS: 00000202 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000055558a5ef400 RCX: 00007efc00506777
RDX: 0000000000000002 RSI: 00007efc005586de RDI: 0000000000000003
RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007fff1f51a228
R13: 0000000000000002 R14: 00007efc005825a0 R15: 0000000000000002
 </TASK>
Modules linked in:
CR2: fffffffffffffeb0
---[ end trace 0000000000000000 ]---
RIP: 0010:__lock_acquire+0x41/0x2de0 kernel/locking/lockdep.c:5140
Code: 2d 12 48 89 84 24 e0 00 00 00 65 48 8b 05 0f e3 2d 12 48 89 44 24 08 45 31 f6 83 3d 28 dc 32 0f 00 0f 84 90 14 00 00 48 89 fb <48> 8b 07 48 3d a0 69 92 94 0f 84 7e 14 00 00 45 89 cd 89 cd 41 89
RSP: 0018:ffffc900046978d8 EFLAGS: 00010002
RAX: ffff88801ff11f40 RBX: fffffffffffffeb0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: fffffffffffffeb0
RBP: ffff88801ff11f40 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000100 R11: 0000000000000007 R12: fffffffffffffeb0
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000246
FS:  000055558a5ef400(0000) GS:ffff888124716000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffffffffeb0 CR3: 00000000452a0000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	2d 12 48 89 84       	sub    $0x84894812,%eax
   5:	24 e0                	and    $0xe0,%al
   7:	00 00                	add    %al,(%rax)
   9:	00 65 48             	add    %ah,0x48(%rbp)
   c:	8b 05 0f e3 2d 12    	mov    0x122de30f(%rip),%eax        # 0x122de321
  12:	48 89 44 24 08       	mov    %rax,0x8(%rsp)
  17:	45 31 f6             	xor    %r14d,%r14d
  1a:	83 3d 28 dc 32 0f 00 	cmpl   $0x0,0xf32dc28(%rip)        # 0xf32dc49
  21:	0f 84 90 14 00 00    	je     0x14b7
  27:	48 89 fb             	mov    %rdi,%rbx
* 2a:	48 8b 07             	mov    (%rdi),%rax <-- trapping instruction
  2d:	48 3d a0 69 92 94    	cmp    $0xffffffff949269a0,%rax
  33:	0f 84 7e 14 00 00    	je     0x14b7
  39:	45 89 cd             	mov    %r9d,%r13d
  3c:	89 cd                	mov    %ecx,%ebp
  3e:	41                   	rex.B
  3f:	89                   	.byte 0x89


---
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Re: [syzbot] [net?] BUG: unable to handle kernel paging request in nsim_drv_port_add (2)

[Jiayuan Chen]

On 11/1/26 3:01 PM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    36aad21d50d1 Merge tag 'ksmbd-for-7.4-rc1-part2' of git://..
> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> console output: https://syzkaller.appspot.com/x/log.txt?x=1332b159580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=dc4462df6d1062fe
> dashboard link: https://syzkaller.appspot.com/bug?extid=b3fca27eb4005f0111f4
> compiler:       Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1194b795580000
>
> AI-generated root cause summary:
> In netdevsim, sysfs device attributes such as 'new_port' and 'del_port' are
> exposed at the device level on nsim_bus_dev without holding device_lock or
> checking if the driver is bound. An access via sysfs after the driver has been
> unbound, after a failed probe, or concurrently with device removal finds drvdata
> set to NULL; passing this NULL pointer to priv_to_devlink() computes a negative
> offset from NULL, triggering a kernel page fault crash when attempting to
> acquire devlink->lock.
>
> full analysis:  https://syzkaller.appspot.com/x/ai_root_cause?x=b3fca27eb4005f0111f4


This looks like the same issue Jiacheng's pending patch addresses,

new_port/del_port don't take device_lock nor check drvdata, so a write
after unbind hits a NULL nsim_dev:

https://lore.kernel.org/netdev/20261012135941.78329-1-stitch@zju.edu.cn/