net/tls: add a TX lock

TLS TX needs to release and re-acquire the socket lock if send buffer
fills up.

TLS SW TX path currently depends on only allowing one thread to enter
the function by the abuse of sk_write_pending. If another writer is
already waiting for memory no new ones are allowed in.

This has two problems:
 - writers don't wake other threads up when they leave the kernel;
   meaning that this scheme works for single extra thread (second
   application thread or delayed work) because memory becoming
   available will send a wake up request, but as Mallesham and
   Pooja report with larger number of threads it leads to threads
   being put to sleep indefinitely;
 - the delayed work does not get _scheduled_ but it may _run_ when
   other writers are present leading to crashes as writers don't
   expect state to change under their feet (same records get pushed
   and freed multiple times); it's hard to reliably bail from the
   work, however, because the mere presence of a writer does not
   guarantee that the writer will push pending records before exiting.

Ensuring wakeups always happen will make the code basically open
code a mutex. Just use a mutex.

The TLS HW TX path does not have any locking (not even the
sk_write_pending hack), yet it uses a per-socket sg_tx_data
array to push records.

Fixes: a42055e8d2c3 ("net/tls: Add support for async encryption of records for performance")
Reported-by: Mallesham  Jatharakonda <mallesh537@gmail.com>
Reported-by: Pooja Trivedi <poojatrivedi@gmail.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 15 insertions, 14 deletions

diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index 5a3715ddc592..683d00837693 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -523,8 +523,10 @@ last_record:
 int tls_device_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 {
         unsigned char record_type = TLS_RECORD_TYPE_DATA;
+        struct tls_context *tls_ctx = tls_get_ctx(sk);
         int rc;
 
+        mutex_lock(&tls_ctx->tx_lock);
         lock_sock(sk);
 
         if (unlikely(msg->msg_controllen)) {
@@ -538,12 +540,14 @@ int tls_device_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
 
 out:
         release_sock(sk);
+        mutex_unlock(&tls_ctx->tx_lock);
         return rc;
 }
 
 int tls_device_sendpage(struct sock *sk, struct page *page,
                         int offset, size_t size, int flags)
 {
+        struct tls_context *tls_ctx = tls_get_ctx(sk);
         struct iov_iter msg_iter;
         char *kaddr = kmap(page);
         struct kvec iov;
@@ -552,6 +556,7 @@ int tls_device_sendpage(struct sock *sk, struct page *page,
         if (flags & MSG_SENDPAGE_NOTLAST)
                 flags |= MSG_MORE;
 
+        mutex_lock(&tls_ctx->tx_lock);
         lock_sock(sk);
 
         if (flags & MSG_OOB) {
@@ -568,6 +573,7 @@ int tls_device_sendpage(struct sock *sk, struct page *page,
 
 out:
         release_sock(sk);
+        mutex_unlock(&tls_ctx->tx_lock);
         return rc;
 }
 
diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
index ac88877dcade..0775ae40fcfb 100644
--- a/net/tls/tls_main.c
+++ b/net/tls/tls_main.c
@@ -267,6 +267,7 @@ void tls_ctx_free(struct sock *sk, struct tls_context *ctx)
 
         memzero_explicit(&ctx->crypto_send, sizeof(ctx->crypto_send));
         memzero_explicit(&ctx->crypto_recv, sizeof(ctx->crypto_recv));
+        mutex_destroy(&ctx->tx_lock);
 
         if (sk)
                 kfree_rcu(ctx, rcu);
@@ -612,6 +613,7 @@ static struct tls_context *create_ctx(struct sock *sk)
         if (!ctx)
                 return NULL;
 
+        mutex_init(&ctx->tx_lock);
         rcu_assign_pointer(icsk->icsk_ulp_data, ctx);
         ctx->sk_proto = sk->sk_prot;
         return ctx;
diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
index e155b792df0b..446f23c1f3ce 100644
--- a/net/tls/tls_sw.c
+++ b/net/tls/tls_sw.c
@@ -897,15 +897,9 @@ int tls_sw_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
         if (msg->msg_flags & ~(MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL))
                 return -ENOTSUPP;
 
+        mutex_lock(&tls_ctx->tx_lock);
         lock_sock(sk);
 
-        /* Wait till there is any pending write on socket */
-        if (unlikely(sk->sk_write_pending)) {
-                ret = wait_on_pending_writer(sk, &timeo);
-                if (unlikely(ret))
-                        goto send_end;
-        }
-
         if (unlikely(msg->msg_controllen)) {
                 ret = tls_proccess_cmsg(sk, msg, &record_type);
                 if (ret) {
@@ -1091,6 +1085,7 @@ send_end:
         ret = sk_stream_error(sk, msg->msg_flags, ret);
 
         release_sock(sk);
+        mutex_unlock(&tls_ctx->tx_lock);
         return copied ? copied : ret;
 }
 
@@ -1114,13 +1109,6 @@ static int tls_sw_do_sendpage(struct sock *sk, struct page *page,
         eor = !(flags & (MSG_MORE | MSG_SENDPAGE_NOTLAST));
         sk_clear_bit(SOCKWQ_ASYNC_NOSPACE, sk);
 
-        /* Wait till there is any pending write on socket */
-        if (unlikely(sk->sk_write_pending)) {
-                ret = wait_on_pending_writer(sk, &timeo);
-                if (unlikely(ret))
-                        goto sendpage_end;
-        }
-
         /* Call the sk_stream functions to manage the sndbuf mem. */
         while (size > 0) {
                 size_t copy, required_size;
@@ -1219,15 +1207,18 @@ sendpage_end:
 int tls_sw_sendpage(struct sock *sk, struct page *page,
                     int offset, size_t size, int flags)
 {
+        struct tls_context *tls_ctx = tls_get_ctx(sk);
         int ret;
 
         if (flags & ~(MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL |
                       MSG_SENDPAGE_NOTLAST | MSG_SENDPAGE_NOPOLICY))
                 return -ENOTSUPP;
 
+        mutex_lock(&tls_ctx->tx_lock);
         lock_sock(sk);
         ret = tls_sw_do_sendpage(sk, page, offset, size, flags);
         release_sock(sk);
+        mutex_unlock(&tls_ctx->tx_lock);
         return ret;
 }
 
@@ -2170,9 +2161,11 @@ static void tx_work_handler(struct work_struct *work)
 
         if (!test_and_clear_bit(BIT_TX_SCHEDULED, &ctx->tx_bitmask))
                 return;
+        mutex_lock(&tls_ctx->tx_lock);
         lock_sock(sk);
         tls_tx_records(sk, -1);
         release_sock(sk);
+        mutex_unlock(&tls_ctx->tx_lock);
 }
 
 void tls_sw_write_space(struct sock *sk, struct tls_context *ctx)