Re: [PATCH net v3] gtp: serialize PDP context updates

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Tue, Aug 11, 2026 at 10:20:12AM +0800, Qing Ming wrote:
> PDP contexts can be deleted through GTP_CMD_DELPDP or while the GTP
> network device is being unregistered. The latter is serialized by RTNL,
> but the generic-netlink delete path only holds RCU.
> 
> Running both paths concurrently can therefore make both paths delete the
> same PDP context. The issue was found through static analysis and
> reproduced on a KASAN-enabled kernel by a two-thread program
> racing GTP_CMD_DELPDP against RTM_DELLINK:
> 
>   Oops: general protection fault, probably for non-canonical address
>   KASAN: maybe wild-memory-access in range
>          [0xdead000000000120-0xdead000000000127]
>   RIP: gtp_genl_del_pdp+0x1c1/0x420 [gtp]
>   RBP: dead000000000122
> 
> The second deletion dereferenced the poisoned hlist pprev pointer.
> 
> Serialize PDP context updates with a mutex shared by gtp_pdp_add(),
> gtp_genl_del_pdp(), and gtp_dellink().
> 
> Fixes: 459aa660eb1d ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)")
> Assisted-by: Codex:gpt-5
> Signed-off-by: Qing Ming <a0yami@mailbox.org>
> ---
> v3:
> - Rebase onto net/main.
> 
> v2: https://lore.kernel.org/netdev/20260808124322.5800-1-a0yami@mailbox.org/
> - Use a dedicated mutex instead of RTNL.
> - Protect PDP add, delete, and link teardown with the same mutex.
> 
>  drivers/net/gtp.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
> index 9a12cc53da00..8ee516debeed 100644
> --- a/drivers/net/gtp.c
> +++ b/drivers/net/gtp.c
[...]
> @@ -2134,6 +2140,8 @@ static int gtp_genl_del_pdp(struct sk_buff *skb, struct genl_info *info)
>  	if (!info->attrs[GTPA_VERSION])
>  		return -EINVAL;
>  
> +	mutex_lock(&gtp_pdp_lock);
> +
>  	rcu_read_lock();

This rcu_read_lock() can go away after adding this new mutex.

>  	pctx = gtp_find_pdp(sock_net(skb->sk), info->attrs);
> @@ -2154,6 +2162,7 @@ static int gtp_genl_del_pdp(struct sk_buff *skb, struct genl_info *info)
>  
>  out_unlock:
>  	rcu_read_unlock();

This can go away too, for gtp_genl_del_pdp(), the mutex replaces this
incorrect rcu read size lock.

Thanks.

> +	mutex_unlock(&gtp_pdp_lock);
>  	return err;
>  }
>  
> -- 
> 2.53.0
>