[syzbot] [net?] general protection fault in rtnl_create_link

[syzbot] [net?] general protection fault in rtnl_create_link

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    eaa517b77e63 ethtool: cmis_cdb: Fix incorrect read / write..
git tree:       net
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1541f23f980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f2054704dd53fb80
dashboard link: https://syzkaller.appspot.com/bug?extid=de1c7d68a10e3f123bdd
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1429874c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1353f74c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8ff6a34dbd2f/disk-eaa517b7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/80dc0689a89b/vmlinux-eaa517b7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/093b749f228d/bzImage-eaa517b7.xz

The issue was bisected to:

commit 04efcee6ef8d0f01eef495db047e7216d6e6e38f
Author: Stanislav Fomichev <sdf@fomichev.me>
Date:   Fri Apr 4 16:11:22 2025 +0000

    net: hold instance lock during NETDEV_CHANGE

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=151db7e4580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=171db7e4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=131db7e4580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+de1c7d68a10e3f123bdd@syzkaller.appspotmail.com
Fixes: 04efcee6ef8d ("net: hold instance lock during NETDEV_CHANGE")

netlink: 4 bytes leftover after parsing attributes in process `syz-executor402'.
netlink: 'syz-executor402': attribute type 15 has an invalid length.
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000055: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000002a8-0x00000000000002af]
CPU: 0 UID: 0 PID: 5841 Comm: syz-executor402 Not tainted 6.14.0-syzkaller-13348-geaa517b77e63 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
RIP: 0010:netdev_need_ops_lock include/net/netdev_lock.h:33 [inline]
RIP: 0010:netdev_lock_ops include/net/netdev_lock.h:41 [inline]
RIP: 0010:rtnl_create_link+0x6af/0xea0 net/core/rtnetlink.c:3680
Code: 24 20 42 80 3c 28 00 74 08 48 89 df e8 4a 3a 3b f8 4c 89 64 24 28 bd a8 02 00 00 48 89 5c 24 08 48 03 2b 48 89 e8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 ef e8 22 3a 3b f8 45 31 e4 48 83 7d 00
RSP: 0018:ffffc900040b6e70 EFLAGS: 00010206
RAX: 0000000000000055 RBX: ffff888035860008 RCX: ffff888030a01e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00000000000002a8 R08: ffffffff89f245f9 R09: 1ffff92000816dfa
R10: dffffc0000000000 R11: fffff52000816dfb R12: ffff8880212e0080
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff888035860000
FS:  000055556170f380(0000) GS:ffff888124f96000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000045ad50 CR3: 000000007c1d2000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 rtnl_newlink_create+0x2f2/0xcb0 net/core/rtnetlink.c:3826
 __rtnl_newlink net/core/rtnetlink.c:3953 [inline]
 rtnl_newlink+0x18b0/0x1fe0 net/core/rtnetlink.c:4068
 rtnetlink_rcv_msg+0x80f/0xd70 net/core/rtnetlink.c:6958
 netlink_rcv_skb+0x208/0x480 net/netlink/af_netlink.c:2534
 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline]
 netlink_unicast+0x7f8/0x9a0 net/netlink/af_netlink.c:1339
 netlink_sendmsg+0x8c3/0xcd0 net/netlink/af_netlink.c:1883
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg+0x221/0x270 net/socket.c:727
 ____sys_sendmsg+0x523/0x860 net/socket.c:2566
 ___sys_sendmsg net/socket.c:2620 [inline]
 __sys_sendmsg+0x271/0x360 net/socket.c:2652
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff3d9feac39
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe861803d8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff3d9feac39
RDX: 0000000004000000 RSI: 0000200000000000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000006 R09: 0000000000000006
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000200000000110 R14: 0000200000000088 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:netdev_need_ops_lock include/net/netdev_lock.h:33 [inline]
RIP: 0010:netdev_lock_ops include/net/netdev_lock.h:41 [inline]
RIP: 0010:rtnl_create_link+0x6af/0xea0 net/core/rtnetlink.c:3680
Code: 24 20 42 80 3c 28 00 74 08 48 89 df e8 4a 3a 3b f8 4c 89 64 24 28 bd a8 02 00 00 48 89 5c 24 08 48 03 2b 48 89 e8 48 c1 e8 03 <42> 80 3c 28 00 74 08 48 89 ef e8 22 3a 3b f8 45 31 e4 48 83 7d 00
RSP: 0018:ffffc900040b6e70 EFLAGS: 00010206
RAX: 0000000000000055 RBX: ffff888035860008 RCX: ffff888030a01e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00000000000002a8 R08: ffffffff89f245f9 R09: 1ffff92000816dfa
R10: dffffc0000000000 R11: fffff52000816dfb R12: ffff8880212e0080
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff888035860000
FS:  000055556170f380(0000) GS:ffff888125096000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000140 CR3: 000000007c1d2000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	24 20                	and    $0x20,%al
   2:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1)
   7:	74 08                	je     0x11
   9:	48 89 df             	mov    %rbx,%rdi
   c:	e8 4a 3a 3b f8       	call   0xf83b3a5b
  11:	4c 89 64 24 28       	mov    %r12,0x28(%rsp)
  16:	bd a8 02 00 00       	mov    $0x2a8,%ebp
  1b:	48 89 5c 24 08       	mov    %rbx,0x8(%rsp)
  20:	48 03 2b             	add    (%rbx),%rbp
  23:	48 89 e8             	mov    %rbp,%rax
  26:	48 c1 e8 03          	shr    $0x3,%rax
* 2a:	42 80 3c 28 00       	cmpb   $0x0,(%rax,%r13,1) <-- trapping instruction
  2f:	74 08                	je     0x39
  31:	48 89 ef             	mov    %rbp,%rdi
  34:	e8 22 3a 3b f8       	call   0xf83b3a5b
  39:	45 31 e4             	xor    %r12d,%r12d
  3c:	48                   	rex.W
  3d:	83                   	.byte 0x83
  3e:	7d 00                	jge    0x40


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
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If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

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#syz undup

Re: [syzbot] [net?] general protection fault in rtnl_create_link

[Kuniyuki Iwashima]

From: syzbot <syzbot+de1c7d68a10e3f123bdd@syzkaller.appspotmail.com>
Date: Sun, 13 Apr 2025 19:14:29 -0700
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    eaa517b77e63 ethtool: cmis_cdb: Fix incorrect read / write..
> git tree:       net
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1541f23f980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f2054704dd53fb80
> dashboard link: https://syzkaller.appspot.com/bug?extid=de1c7d68a10e3f123bdd
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1429874c580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1353f74c580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/8ff6a34dbd2f/disk-eaa517b7.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/80dc0689a89b/vmlinux-eaa517b7.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/093b749f228d/bzImage-eaa517b7.xz
> 
> The issue was bisected to:
> 
> commit 04efcee6ef8d0f01eef495db047e7216d6e6e38f
> Author: Stanislav Fomichev <sdf@fomichev.me>
> Date:   Fri Apr 4 16:11:22 2025 +0000
> 
>     net: hold instance lock during NETDEV_CHANGE
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=151db7e4580000
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=171db7e4580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=131db7e4580000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+de1c7d68a10e3f123bdd@syzkaller.appspotmail.com
> Fixes: 04efcee6ef8d ("net: hold instance lock during NETDEV_CHANGE")
> 
> netlink: 4 bytes leftover after parsing attributes in process `syz-executor402'.
> netlink: 'syz-executor402': attribute type 15 has an invalid length.
> Oops: general protection fault, probably for non-canonical address 0xdffffc0000000055: 0000 [#1] SMP KASAN PTI
> KASAN: null-ptr-deref in range [0x00000000000002a8-0x00000000000002af]
> CPU: 0 UID: 0 PID: 5841 Comm: syz-executor402 Not tainted 6.14.0-syzkaller-13348-geaa517b77e63 #0 PREEMPT(full) 
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
> RIP: 0010:netdev_need_ops_lock include/net/netdev_lock.h:33 [inline]
> RIP: 0010:netdev_lock_ops include/net/netdev_lock.h:41 [inline]
> RIP: 0010:rtnl_create_link+0x6af/0xea0 net/core/rtnetlink.c:3680

#syz test

diff --git a/include/net/netdev_lock.h b/include/net/netdev_lock.h
index 5706835a660c..270e157a4a79 100644
--- a/include/net/netdev_lock.h
+++ b/include/net/netdev_lock.h
@@ -30,7 +30,8 @@ static inline bool netdev_need_ops_lock(const struct net_device *dev)
 	bool ret = dev->request_ops_lock || !!dev->queue_mgmt_ops;
 
 #if IS_ENABLED(CONFIG_NET_SHAPER)
-	ret |= !!dev->netdev_ops->net_shaper_ops;
+	if (dev->netdev_ops)
+		ret |= !!dev->netdev_ops->net_shaper_ops;
 #endif
 
 	return ret;

Re: [syzbot] [net?] general protection fault in rtnl_create_link

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
unregister_netdevice: waiting for DEV to become free

unregister_netdevice: waiting for batadv0 to become free. Usage count = 3


Tested on:

commit:         8c941f14 Merge branch 'there-are-some-bugfix-for-hibmc..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=15bab398580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=eecd7902e39d7933
dashboard link: https://syzkaller.appspot.com/bug?extid=de1c7d68a10e3f123bdd
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1661c0cc580000

Re: [syzbot] [net?] general protection fault in rtnl_create_link

[Jakub Kicinski]

On Sun, 13 Apr 2025 19:30:46 -0700 Kuniyuki Iwashima wrote:
> diff --git a/include/net/netdev_lock.h b/include/net/netdev_lock.h
> index 5706835a660c..270e157a4a79 100644
> --- a/include/net/netdev_lock.h
> +++ b/include/net/netdev_lock.h
> @@ -30,7 +30,8 @@ static inline bool netdev_need_ops_lock(const struct net_device *dev)
>  	bool ret = dev->request_ops_lock || !!dev->queue_mgmt_ops;
>  
>  #if IS_ENABLED(CONFIG_NET_SHAPER)
> -	ret |= !!dev->netdev_ops->net_shaper_ops;
> +	if (dev->netdev_ops)
> +		ret |= !!dev->netdev_ops->net_shaper_ops;
>  #endif

This is a bit surprising, we pretty much never validate if dev has ops.

I think we're guaranteed that IFF_UP will not be set if we just
allocated the device, so we can remove the locks in rtnl_create_link()
and to double confirm add a netdev_ops_assert_locked_or_invisible() 
in netif_state_change() ?

Re: [syzbot] [net?] general protection fault in rtnl_create_link

[Kuniyuki Iwashima]

From: Jakub Kicinski <kuba@kernel.org>
Date: Mon, 14 Apr 2025 10:37:27 -0700
> On Sun, 13 Apr 2025 19:30:46 -0700 Kuniyuki Iwashima wrote:
> > diff --git a/include/net/netdev_lock.h b/include/net/netdev_lock.h
> > index 5706835a660c..270e157a4a79 100644
> > --- a/include/net/netdev_lock.h
> > +++ b/include/net/netdev_lock.h
> > @@ -30,7 +30,8 @@ static inline bool netdev_need_ops_lock(const struct net_device *dev)
> >  	bool ret = dev->request_ops_lock || !!dev->queue_mgmt_ops;
> >  
> >  #if IS_ENABLED(CONFIG_NET_SHAPER)
> > -	ret |= !!dev->netdev_ops->net_shaper_ops;
> > +	if (dev->netdev_ops)
> > +		ret |= !!dev->netdev_ops->net_shaper_ops;
> >  #endif
> 
> This is a bit surprising, we pretty much never validate if dev has ops.
> 
> I think we're guaranteed that IFF_UP will not be set if we just
> allocated the device, so we can remove the locks in rtnl_create_link()
> and to double confirm add a netdev_ops_assert_locked_or_invisible() 
> in netif_state_change() ?

Removing the lock from NEWLINK makes sense, but my concern
was NETDEV_CHANGE, which will requires more caution ?

commit 04efcee6ef8d0f01eef495db047e7216d6e6e38f
Author: Stanislav Fomichev <sdf@fomichev.me>
Date:   Fri Apr 4 09:11:22 2025 -0700

    net: hold instance lock during NETDEV_CHANGE

Re: [syzbot] [net?] general protection fault in rtnl_create_link

[Jakub Kicinski]

On Mon, 14 Apr 2025 11:01:59 -0700 Kuniyuki Iwashima wrote:
> From: Jakub Kicinski <kuba@kernel.org>
> Date: Mon, 14 Apr 2025 10:37:27 -0700
> > On Sun, 13 Apr 2025 19:30:46 -0700 Kuniyuki Iwashima wrote:  
> > > diff --git a/include/net/netdev_lock.h b/include/net/netdev_lock.h
> > > index 5706835a660c..270e157a4a79 100644
> > > --- a/include/net/netdev_lock.h
> > > +++ b/include/net/netdev_lock.h
> > > @@ -30,7 +30,8 @@ static inline bool netdev_need_ops_lock(const struct net_device *dev)
> > >  	bool ret = dev->request_ops_lock || !!dev->queue_mgmt_ops;
> > >  
> > >  #if IS_ENABLED(CONFIG_NET_SHAPER)
> > > -	ret |= !!dev->netdev_ops->net_shaper_ops;
> > > +	if (dev->netdev_ops)
> > > +		ret |= !!dev->netdev_ops->net_shaper_ops;
> > >  #endif  
> > 
> > This is a bit surprising, we pretty much never validate if dev has ops.
> > 
> > I think we're guaranteed that IFF_UP will not be set if we just
> > allocated the device, so we can remove the locks in rtnl_create_link()
> > and to double confirm add a netdev_ops_assert_locked_or_invisible() 
> > in netif_state_change() ?  
> 
> Removing the lock from NEWLINK makes sense, but my concern
> was NETDEV_CHANGE, which will requires more caution ?
> 
> commit 04efcee6ef8d0f01eef495db047e7216d6e6e38f
> Author: Stanislav Fomichev <sdf@fomichev.me>
> Date:   Fri Apr 4 09:11:22 2025 -0700
> 
>     net: hold instance lock during NETDEV_CHANGE

How could we fire a notifier for a device that hasn't been initialized,
let alone registered?

I'm hoping that the _or_invisible assert in my suggestion will flag to
future developers trying to change netif_state_change() that the device
here may not be fully constructed.

Re: [syzbot] [net?] general protection fault in rtnl_create_link

[Kuniyuki Iwashima]

From: Jakub Kicinski <kuba@kernel.org>
Date: Mon, 14 Apr 2025 11:15:36 -0700
> On Mon, 14 Apr 2025 11:01:59 -0700 Kuniyuki Iwashima wrote:
> > From: Jakub Kicinski <kuba@kernel.org>
> > Date: Mon, 14 Apr 2025 10:37:27 -0700
> > > On Sun, 13 Apr 2025 19:30:46 -0700 Kuniyuki Iwashima wrote:  
> > > > diff --git a/include/net/netdev_lock.h b/include/net/netdev_lock.h
> > > > index 5706835a660c..270e157a4a79 100644
> > > > --- a/include/net/netdev_lock.h
> > > > +++ b/include/net/netdev_lock.h
> > > > @@ -30,7 +30,8 @@ static inline bool netdev_need_ops_lock(const struct net_device *dev)
> > > >  	bool ret = dev->request_ops_lock || !!dev->queue_mgmt_ops;
> > > >  
> > > >  #if IS_ENABLED(CONFIG_NET_SHAPER)
> > > > -	ret |= !!dev->netdev_ops->net_shaper_ops;
> > > > +	if (dev->netdev_ops)
> > > > +		ret |= !!dev->netdev_ops->net_shaper_ops;
> > > >  #endif  
> > > 
> > > This is a bit surprising, we pretty much never validate if dev has ops.
> > > 
> > > I think we're guaranteed that IFF_UP will not be set if we just
> > > allocated the device, so we can remove the locks in rtnl_create_link()
> > > and to double confirm add a netdev_ops_assert_locked_or_invisible() 
> > > in netif_state_change() ?  
> > 
> > Removing the lock from NEWLINK makes sense, but my concern
> > was NETDEV_CHANGE, which will requires more caution ?
> > 
> > commit 04efcee6ef8d0f01eef495db047e7216d6e6e38f
> > Author: Stanislav Fomichev <sdf@fomichev.me>
> > Date:   Fri Apr 4 09:11:22 2025 -0700
> > 
> >     net: hold instance lock during NETDEV_CHANGE
> 
> How could we fire a notifier for a device that hasn't been initialized,
> let alone registered?

Ah, now got it.  Exactly, we won't trigger NETDEV_CHANGE in the path,
rtnl_configure_link() is the place where IFF_UP is flagged later also
under the ops lock.


> 
> I'm hoping that the _or_invisible assert in my suggestion will flag to
> future developers trying to change netif_state_change() that the device
> here may not be fully constructed.

Totally agree now.