Re: [PATCH v2] net/smc: release the internal TCP sock on IPPROTO_SMC socket creation failure

[Sidraya Jayagond <sidraya@linux.ibm.com>]

On 13/08/26 11:34 am, Chuyf26 wrote:
> IPPROTO_SMC sockets create an internal TCP sock ("clcsock") from the
> proto->init hook. When socket creation fails after proto->init has
> run - e.g. a cgroup BPF program attached to BPF_CGROUP_INET_SOCK_CREATE
> denies the socket - sk_common_release() only invokes sk_prot->destroy
> if it is set, but neither smc_inet_prot nor smc_inet6_prot defines it,
> and smc_destruct() returns early unless sk_state is SMC_CLOSED. As a
> result, every failing socket(AF_INET, SOCK_STREAM, IPPROTO_SMC) call
> leaks one tcp_sock, so an unprivileged task able to attach a deny-all
> BPF_CGROUP_INET_SOCK_CREATE program to its own cgroup can grow kernel
> memory unboundedly.
> 
> Add a .destroy hook to both protos that releases the clcsock via
> smc_clcsock_release(), which is safe here because it skips a NULL
> clcsock under clcsock_release_lock. Also initialize clcsock to NULL
> when setting the sock up: the smc_sock slab is SLAB_TYPESAFE_BY_RCU,
> so recycled objects are not zeroed.
> 
> Fixes: d25a92ccae6b ("net/smc: Introduce IPPROTO_SMC")
> Reported-by: Abaci <abaci@linux.alibaba.com>
> Assisted-by: abaci:qwen3.8-max
> Signed-off-by: Chuyf26 <Chuyf26@linux.alibaba.com>
> ---
>  net/smc/smc_inet.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/net/smc/smc_inet.c b/net/smc/smc_inet.c
> index a94084b..b94a194 100644
> --- a/net/smc/smc_inet.c
> +++ b/net/smc/smc_inet.c
> @@ -15,13 +15,16 @@
>  
>  #include "smc_inet.h"
>  #include "smc.h"
> +#include "smc_close.h"
>  
>  static int smc_inet_init_sock(struct sock *sk);
> +static void smc_inet_destroy_sock(struct sock *sk);
>  
>  static struct proto smc_inet_prot = {
>  	.name		= "INET_SMC",
>  	.owner		= THIS_MODULE,
>  	.init		= smc_inet_init_sock,
> +	.destroy	= smc_inet_destroy_sock,
>  	.hash		= smc_hash_sk,
>  	.unhash		= smc_unhash_sk,
>  	.release_cb	= smc_release_cb,
> @@ -68,6 +71,7 @@ static struct proto smc_inet6_prot = {
>  	.name		= "INET6_SMC",
>  	.owner		= THIS_MODULE,
>  	.init		= smc_inet_init_sock,
> +	.destroy	= smc_inet_destroy_sock,
>  	.hash		= smc_hash_sk,
>  	.unhash		= smc_unhash_sk,
>  	.release_cb	= smc_release_cb,
> @@ -109,6 +113,14 @@ static struct inet_protosw smc_inet6_protosw = {
>  static int smc_inet_init_sock(struct sock *sk)
>  {
>  	struct net *net = sock_net(sk);
> +	struct smc_sock *smc = smc_sk(sk);
> +
> +	/*
> +	 * The smc_sock slab is SLAB_TYPESAFE_BY_RCU and recycled objects
> +	 * are not zeroed. .destroy may run even if .init never completed,
> +	 * so make sure smc_clcsock_release() sees a valid clcsock.
> +	 */
> +	smc->clcsock = NULL;
>  
>  	/* init common smc sock */
>  	smc_sk_init(net, sk, IPPROTO_SMC);
> @@ -116,6 +128,17 @@ static int smc_inet_init_sock(struct sock *sk)
>  	return smc_create_clcsk(net, sk, sk->sk_family);
>  }
>  
> +static void smc_inet_destroy_sock(struct sock *sk)
> +{
> +	/*
> +	 * If inet_create()/inet6_create() fail after .init has created the
> +	 * internal TCP sock (e.g. rejected by a cgroup BPF program),
> +	 * sk_common_release() ends up here. Release the TCP sock, otherwise
> +	 * it leaks on every failed IPPROTO_SMC socket() call.
> +	 */
> +	smc_clcsock_release(smc_sk(sk));
> +}
> +
>  int __init smc_inet_init(void)
>  {
>  	int rc;

Thank you for fixing this.
Reviewed-by: Sidraya Jayagond <sidraya@linux.ibm.com>