BUG/MEDIUM: ssl: wrong eviction from the session cache tree

When using WolfSSL, there are some cases were the SSL_CTX_sess_new_cb is
called with an existing session ID. These cases are not met with
OpenSSL.

When the ID is found in the session tree during the insertion, the
shared_block len is not set to 0 and is not used. However if later the
block is reused, since the len is not set to 0, the release callback
will be called an ebmb_delete will be tried on the block, even if it's
not in the tree, provoking a crash.

The code was buggy from the beginning, but the case never happen with
openssl which changes the ID.

Must be backported in every maintained branches.

src/ssl_sock.c

@@ -4211,6 +4211,7 @@ static int sh_ssl_sess_store(unsigned char *s_id, unsigned char *data, int data_
 	if (oldsh_ssl_sess != sh_ssl_sess) {
 		 /* NOTE: Row couldn't be in use because we lock read & write function */
 		/* release the reserved row */
+		first->len = 0; /* the len must be liberated in order not to call the release callback on it */
 		shctx_row_dec_hot(ssl_shctx, first);
 		/* replace the previous session already in the tree */
 		sh_ssl_sess = oldsh_ssl_sess;