Re: [PATCH 2/2] net/tcp: Disable TCP-MD5 static key on tcp_md5sig_info destruction

From: Eric Dumazet
Date: Wed Nov 02 2022 - 17:25:39 EST

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In reply to: Dmitry Safonov: "[PATCH 2/2] net/tcp: Disable TCP-MD5 static key on tcp_md5sig_info destruction"
Next in thread: Dmitry Safonov: "Re: [PATCH 2/2] net/tcp: Disable TCP-MD5 static key on tcp_md5sig_info destruction"
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On Wed, Nov 2, 2022 at 2:14 PM Dmitry Safonov <dima@xxxxxxxxxx> wrote:
>
> To do that, separate two scenarios:
> - where it's the first MD5 key on the system, which means that enabling
> of the static key may need to sleep;
> - copying of an existing key from a listening socket to the request
> socket upon receiving a signed TCP segment, where static key was
> already enabled (when the key was added to the listening socket).
>
> Now the life-time of the static branch for TCP-MD5 is until:
> - last tcp_md5sig_info is destroyed
> - last socket in time-wait state with MD5 key is closed.
>
> Which means that after all sockets with TCP-MD5 keys are gone, the
> system gets back the performance of disabled md5-key static branch.
>
> Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx>
> ---
> include/net/tcp.h | 10 ++++---
> net/ipv4/tcp.c | 5 +---
> net/ipv4/tcp_ipv4.c | 56 ++++++++++++++++++++++++++++++----------
> net/ipv4/tcp_minisocks.c | 9 ++++---
> net/ipv4/tcp_output.c | 4 +--
> net/ipv6/tcp_ipv6.c | 10 +++----
> 6 files changed, 63 insertions(+), 31 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 14d45661a84d..a0cdf013782a 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -1675,7 +1675,11 @@ int tcp_v4_md5_hash_skb(char *md5_hash, const struct tcp_md5sig_key *key,
> const struct sock *sk, const struct sk_buff *skb);
> int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
> int family, u8 prefixlen, int l3index, u8 flags,
> - const u8 *newkey, u8 newkeylen, gfp_t gfp);
> + const u8 *newkey, u8 newkeylen);
> +int tcp_md5_key_copy(struct sock *sk, const union tcp_md5_addr *addr,
> + int family, u8 prefixlen, int l3index,
> + struct tcp_md5sig_key *key);
> +
> int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr,
> int family, u8 prefixlen, int l3index, u8 flags);
> struct tcp_md5sig_key *tcp_v4_md5_lookup(const struct sock *sk,
> @@ -1683,7 +1687,7 @@ struct tcp_md5sig_key *tcp_v4_md5_lookup(const struct sock *sk,
>
> #ifdef CONFIG_TCP_MD5SIG
> #include <linux/jump_label.h>
> -extern struct static_key_false tcp_md5_needed;
> +extern struct static_key_false_deferred tcp_md5_needed;
> struct tcp_md5sig_key *__tcp_md5_do_lookup(const struct sock *sk, int l3index,
> const union tcp_md5_addr *addr,
> int family);
> @@ -1691,7 +1695,7 @@ static inline struct tcp_md5sig_key *
> tcp_md5_do_lookup(const struct sock *sk, int l3index,
> const union tcp_md5_addr *addr, int family)
> {
> - if (!static_branch_unlikely(&tcp_md5_needed))
> + if (!static_branch_unlikely(&tcp_md5_needed.key))
> return NULL;
> return __tcp_md5_do_lookup(sk, l3index, addr, family);
> }
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index ef14efa1fb70..936ed566cc89 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -4460,11 +4460,8 @@ bool tcp_alloc_md5sig_pool(void)
> if (unlikely(!READ_ONCE(tcp_md5sig_pool_populated))) {
> mutex_lock(&tcp_md5sig_mutex);
>
> - if (!tcp_md5sig_pool_populated) {
> + if (!tcp_md5sig_pool_populated)
> __tcp_alloc_md5sig_pool();
> - if (tcp_md5sig_pool_populated)
> - static_branch_inc(&tcp_md5_needed);
> - }
>
> mutex_unlock(&tcp_md5sig_mutex);
> }
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index fae80b1a1796..f812d507fc9a 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -1064,7 +1064,7 @@ static void tcp_v4_reqsk_destructor(struct request_sock *req)
> * We need to maintain these in the sk structure.
> */
>
> -DEFINE_STATIC_KEY_FALSE(tcp_md5_needed);
> +DEFINE_STATIC_KEY_DEFERRED_FALSE(tcp_md5_needed, HZ);
> EXPORT_SYMBOL(tcp_md5_needed);
>
> static bool better_md5_match(struct tcp_md5sig_key *old, struct tcp_md5sig_key *new)
> @@ -1177,9 +1177,6 @@ static int tcp_md5sig_info_add(struct sock *sk, gfp_t gfp)
> struct tcp_sock *tp = tcp_sk(sk);
> struct tcp_md5sig_info *md5sig;
>
> - if (rcu_dereference_protected(tp->md5sig_info, lockdep_sock_is_held(sk)))
> - return 0;
> -
> md5sig = kmalloc(sizeof(*md5sig), gfp);
> if (!md5sig)
> return -ENOMEM;
> @@ -1191,9 +1188,9 @@ static int tcp_md5sig_info_add(struct sock *sk, gfp_t gfp)
> }
>
> /* This can be called on a newly created socket, from other files */
> -int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
> - int family, u8 prefixlen, int l3index, u8 flags,
> - const u8 *newkey, u8 newkeylen, gfp_t gfp)
> +static int __tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
> + int family, u8 prefixlen, int l3index, u8 flags,
> + const u8 *newkey, u8 newkeylen, gfp_t gfp)
> {
> /* Add Key to the list */
> struct tcp_md5sig_key *key;
> @@ -1220,9 +1217,6 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
> return 0;
> }
>
> - if (tcp_md5sig_info_add(sk, gfp))
> - return -ENOMEM;
> -
> md5sig = rcu_dereference_protected(tp->md5sig_info,
> lockdep_sock_is_held(sk));
>
> @@ -1246,8 +1240,44 @@ int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
> hlist_add_head_rcu(&key->node, &md5sig->head);
> return 0;
> }
> +
> +int tcp_md5_do_add(struct sock *sk, const union tcp_md5_addr *addr,
> + int family, u8 prefixlen, int l3index, u8 flags,
> + const u8 *newkey, u8 newkeylen)
> +{
> + struct tcp_sock *tp = tcp_sk(sk);
> +
> + if (!rcu_dereference_protected(tp->md5sig_info, lockdep_sock_is_held(sk))) {
> + if (tcp_md5sig_info_add(sk, GFP_KERNEL))
> + return -ENOMEM;
> +
> + static_branch_inc(&tcp_md5_needed.key);
> + }
> +
> + return __tcp_md5_do_add(sk, addr, family, prefixlen, l3index, flags,
> + newkey, newkeylen, GFP_KERNEL);
> +}
> EXPORT_SYMBOL(tcp_md5_do_add);
>
> +int tcp_md5_key_copy(struct sock *sk, const union tcp_md5_addr *addr,
> + int family, u8 prefixlen, int l3index,
> + struct tcp_md5sig_key *key)
> +{
> + struct tcp_sock *tp = tcp_sk(sk);
> +
> + if (!rcu_dereference_protected(tp->md5sig_info, lockdep_sock_is_held(sk))) {
> + if (tcp_md5sig_info_add(sk, sk_gfp_mask(sk, GFP_ATOMIC)))
> + return -ENOMEM;
> +
> + atomic_inc(&tcp_md5_needed.key.key.enabled);

static_branch_inc ?

> + }
> +
> + return __tcp_md5_do_add(sk, addr, family, prefixlen, l3index,
> + key->flags, key->key, key->keylen,
> + sk_gfp_mask(sk, GFP_ATOMIC));
> +}
> +EXPORT_SYMBOL(tcp_md5_key_copy);
> +
> int tcp_md5_do_del(struct sock *sk, const union tcp_md5_addr *addr, int family,
> u8 prefixlen, int l3index, u8 flags)
> {
> @@ -1334,7 +1364,7 @@ static int tcp_v4_parse_md5_keys(struct sock *sk, int optname,
> return -EINVAL;
>
> return tcp_md5_do_add(sk, addr, AF_INET, prefixlen, l3index, flags,
> - cmd.tcpm_key, cmd.tcpm_keylen, GFP_KERNEL);
> + cmd.tcpm_key, cmd.tcpm_keylen);
> }
>
> static int tcp_v4_md5_hash_headers(struct tcp_md5sig_pool *hp,
> @@ -1591,8 +1621,7 @@ struct sock *tcp_v4_syn_recv_sock(const struct sock *sk, struct sk_buff *skb,
> * memory, then we end up not copying the key
> * across. Shucks.
> */
> - tcp_md5_do_add(newsk, addr, AF_INET, 32, l3index, key->flags,
> - key->key, key->keylen, GFP_ATOMIC);
> + tcp_md5_key_copy(newsk, addr, AF_INET, 32, l3index, key);
> sk_gso_disable(newsk);
> }
> #endif
> @@ -2284,6 +2313,7 @@ void tcp_v4_destroy_sock(struct sock *sk)
> tcp_clear_md5_list(sk);
> kfree_rcu(rcu_dereference_protected(tp->md5sig_info, 1), rcu);
> tp->md5sig_info = NULL;
> + static_branch_slow_dec_deferred(&tcp_md5_needed);
> }
> #endif
>
> diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
> index c375f603a16c..fb500160b8d2 100644
> --- a/net/ipv4/tcp_minisocks.c
> +++ b/net/ipv4/tcp_minisocks.c
> @@ -291,13 +291,14 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
> */
> do {
> tcptw->tw_md5_key = NULL;
> - if (static_branch_unlikely(&tcp_md5_needed)) {
> + if (static_branch_unlikely(&tcp_md5_needed.key)) {
> struct tcp_md5sig_key *key;
>
> key = tp->af_specific->md5_lookup(sk, sk);
> if (key) {
> tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC);
> BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool());
> + atomic_inc(&tcp_md5_needed.key.key.enabled);

static_branch_inc

> }
> }
> } while (0);
> @@ -337,11 +338,13 @@ EXPORT_SYMBOL(tcp_time_wait);
> void tcp_twsk_destructor(struct sock *sk)
> {
> #ifdef CONFIG_TCP_MD5SIG
> - if (static_branch_unlikely(&tcp_md5_needed)) {
> + if (static_branch_unlikely(&tcp_md5_needed.key)) {
> struct tcp_timewait_sock *twsk = tcp_twsk(sk);
>
> - if (twsk->tw_md5_key)
> + if (twsk->tw_md5_key) {

Orthogonal to this patch, but I wonder why we do not clear
twsk->tw_md5_key before kfree_rcu()

It seems a lookup could catch the invalid pointer.

> kfree_rcu(twsk->tw_md5_key, rcu);
> + static_branch_slow_dec_deferred(&tcp_md5_needed);
> + }
> }
> #endif
> }
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index c69f4d966024..86e71c8c76bc 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -766,7 +766,7 @@ static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
>
> *md5 = NULL;
> #ifdef CONFIG_TCP_MD5SIG
> - if (static_branch_unlikely(&tcp_md5_needed) &&
> + if (static_branch_unlikely(&tcp_md5_needed.key) &&
> rcu_access_pointer(tp->md5sig_info)) {
> *md5 = tp->af_specific->md5_lookup(sk, sk);
> if (*md5) {
> @@ -922,7 +922,7 @@ static unsigned int tcp_established_options(struct sock *sk, struct sk_buff *skb
>
> *md5 = NULL;
> #ifdef CONFIG_TCP_MD5SIG
> - if (static_branch_unlikely(&tcp_md5_needed) &&
> + if (static_branch_unlikely(&tcp_md5_needed.key) &&
> rcu_access_pointer(tp->md5sig_info)) {
> *md5 = tp->af_specific->md5_lookup(sk, sk);
> if (*md5) {
> diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
> index 2a3f9296df1e..3e3bdc120fc8 100644
> --- a/net/ipv6/tcp_ipv6.c
> +++ b/net/ipv6/tcp_ipv6.c
> @@ -677,12 +677,11 @@ static int tcp_v6_parse_md5_keys(struct sock *sk, int optname,
> if (ipv6_addr_v4mapped(&sin6->sin6_addr))
> return tcp_md5_do_add(sk, (union tcp_md5_addr *)&sin6->sin6_addr.s6_addr32[3],
> AF_INET, prefixlen, l3index, flags,
> - cmd.tcpm_key, cmd.tcpm_keylen,
> - GFP_KERNEL);
> + cmd.tcpm_key, cmd.tcpm_keylen);
>
> return tcp_md5_do_add(sk, (union tcp_md5_addr *)&sin6->sin6_addr,
> AF_INET6, prefixlen, l3index, flags,
> - cmd.tcpm_key, cmd.tcpm_keylen, GFP_KERNEL);
> + cmd.tcpm_key, cmd.tcpm_keylen);
> }
>
> static int tcp_v6_md5_hash_headers(struct tcp_md5sig_pool *hp,
> @@ -1382,9 +1381,8 @@ static struct sock *tcp_v6_syn_recv_sock(const struct sock *sk, struct sk_buff *
> * memory, then we end up not copying the key
> * across. Shucks.
> */
> - tcp_md5_do_add(newsk, (union tcp_md5_addr *)&newsk->sk_v6_daddr,
> - AF_INET6, 128, l3index, key->flags, key->key, key->keylen,
> - sk_gfp_mask(sk, GFP_ATOMIC));
> + tcp_md5_key_copy(newsk, (union tcp_md5_addr *)&newsk->sk_v6_daddr,
> + AF_INET6, 128, l3index, key);
> }
> #endif
>
> --
> 2.38.1
>

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In reply to: Dmitry Safonov: "[PATCH 2/2] net/tcp: Disable TCP-MD5 static key on tcp_md5sig_info destruction"
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