Re: [PATCH net] llc: do not use skb_get() before dev_queue_xmit()

[Simon Horman <horms@kernel.org>]

On Thu, Feb 27, 2025 at 08:26:42AM +0000, Eric Dumazet wrote:
> syzbot is able to crash hosts [1], using llc and devices
> not supporting IFF_TX_SKB_SHARING.
> 
> In this case, e1000 driver calls eth_skb_pad(), while
> the skb is shared.
> 
> Simply replace skb_get() by skb_clone() in net/llc/llc_s_ac.c
> 
> Note that e1000 driver might have an issue with pktgen,
> because it does not clear IFF_TX_SKB_SHARING, this is an
> orthogonal change.
> 
> We need to audit other skb_get() uses in net/llc.
> 
> [1]
> 
> kernel BUG at net/core/skbuff.c:2178 !
> Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI
> CPU: 0 UID: 0 PID: 16371 Comm: syz.2.2764 Not tainted 6.14.0-rc4-syzkaller-00052-gac9c34d1e45a #0
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
>  RIP: 0010:pskb_expand_head+0x6ce/0x1240 net/core/skbuff.c:2178
> Call Trace:
>  <TASK>
>   __skb_pad+0x18a/0x610 net/core/skbuff.c:2466
>   __skb_put_padto include/linux/skbuff.h:3843 [inline]
>   skb_put_padto include/linux/skbuff.h:3862 [inline]
>   eth_skb_pad include/linux/etherdevice.h:656 [inline]
>   e1000_xmit_frame+0x2d99/0x5800 drivers/net/ethernet/intel/e1000/e1000_main.c:3128
>   __netdev_start_xmit include/linux/netdevice.h:5151 [inline]
>   netdev_start_xmit include/linux/netdevice.h:5160 [inline]
>   xmit_one net/core/dev.c:3806 [inline]
>   dev_hard_start_xmit+0x9a/0x7b0 net/core/dev.c:3822
>   sch_direct_xmit+0x1ae/0xc30 net/sched/sch_generic.c:343
>   __dev_xmit_skb net/core/dev.c:4045 [inline]
>   __dev_queue_xmit+0x13d4/0x43e0 net/core/dev.c:4621
>   dev_queue_xmit include/linux/netdevice.h:3313 [inline]
>   llc_sap_action_send_test_c+0x268/0x320 net/llc/llc_s_ac.c:144
>   llc_exec_sap_trans_actions net/llc/llc_sap.c:153 [inline]
>   llc_sap_next_state net/llc/llc_sap.c:182 [inline]
>   llc_sap_state_process+0x239/0x510 net/llc/llc_sap.c:209
>   llc_ui_sendmsg+0xd0d/0x14e0 net/llc/af_llc.c:993
>   sock_sendmsg_nosec net/socket.c:718 [inline]
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: syzbot+da65c993ae113742a25f@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/67c020c0.050a0220.222324.0011.GAE@google.com/T/#u
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Simon Horman <horms@kernel.org>