Re: [PATCH net] ipv6: reject malicious packets in ipv6_gso_segment()

[Dawid Osuchowski <dawid.osuchowski@linux.intel.com>]

On 2025-07-30 3:17 PM, Eric Dumazet wrote:
> syzbot was able to craft a packet with very long IPv6 extension headers
> leading to an overflow of skb->transport_header.
> 
> This 16bit field has a limited range.
> 
> Add skb_reset_transport_header_careful() helper and use it
> from ipv6_gso_segment()
> 
> WARNING: CPU: 0 PID: 5871 at ./include/linux/skbuff.h:3032 skb_reset_transport_header include/linux/skbuff.h:3032 [inline]
> WARNING: CPU: 0 PID: 5871 at ./include/linux/skbuff.h:3032 ipv6_gso_segment+0x15e2/0x21e0 net/ipv6/ip6_offload.c:151
> Modules linked in:
> CPU: 0 UID: 0 PID: 5871 Comm: syz-executor211 Not tainted 6.16.0-rc6-syzkaller-g7abc678e3084 #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
>   RIP: 0010:skb_reset_transport_header include/linux/skbuff.h:3032 [inline]
>   RIP: 0010:ipv6_gso_segment+0x15e2/0x21e0 net/ipv6/ip6_offload.c:151
> Call Trace:
>   <TASK>
>    skb_mac_gso_segment+0x31c/0x640 net/core/gso.c:53
>    nsh_gso_segment+0x54a/0xe10 net/nsh/nsh.c:110
>    skb_mac_gso_segment+0x31c/0x640 net/core/gso.c:53
>    __skb_gso_segment+0x342/0x510 net/core/gso.c:124
>    skb_gso_segment include/net/gso.h:83 [inline]
>    validate_xmit_skb+0x857/0x11b0 net/core/dev.c:3950
>    validate_xmit_skb_list+0x84/0x120 net/core/dev.c:4000
>    sch_direct_xmit+0xd3/0x4b0 net/sched/sch_generic.c:329
>    __dev_xmit_skb net/core/dev.c:4102 [inline]
>    __dev_queue_xmit+0x17b6/0x3a70 net/core/dev.c:4679
> 
> Fixes: d1da932ed4ec ("ipv6: Separate ipv6 offload support")
> Reported-by: syzbot+af43e647fd835acc02df@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/688a1a05.050a0220.5d226.0008.GAE@google.com/T/#u
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Dawid Osuchowski <dawid.osuchowski@linux.intel.com>

Thanks,
Dawid