TCP input - fix stack buffer overflow in acceptor.

Author: BonnyAD9

src/plugins/input/tcp/src/Acceptor.cpp

@@ -32,6 +32,11 @@
 
 namespace tcp_in {
 
+/** Constexpr implementation of std::max for 3 size_t values. */
+constexpr size_t max(size_t a, size_t b, size_t c) {
+    return a > b ? (a > c ? a : c) : (b > c ? b : c);
+}
+
 Acceptor::Acceptor(ClientManager &clients, ipx_ctx_t *ctx) :
     m_epoll(),
     m_sockets(),
@@ -74,9 +79,11 @@ void Acceptor::add_address(IpAddress &adr, uint16_t port, bool ipv6_only) {
 }
 
 UniqueFd Acceptor::bind_address(IpAddress &addr, uint16_t port, bool ipv6_only) {
-    sockaddr saddr{};
-    auto v4 = reinterpret_cast<sockaddr_in *>(&saddr);
-    auto v6 = reinterpret_cast<sockaddr_in6 *>(&saddr);
+    // Allocate enough data to fit any of the structures.
+    std::array<char, max(sizeof(sockaddr), sizeof(sockaddr_in), sizeof(sockaddr_in6))> addr_data;
+    auto saddr = reinterpret_cast<sockaddr *>(addr_data.data());
+    auto v4 = reinterpret_cast<sockaddr_in *>(saddr);
+    auto v6 = reinterpret_cast<sockaddr_in6 *>(saddr);
     size_t addr_len;
 
     if (addr.version == IpVersion::IP4) {
@@ -94,7 +101,7 @@ UniqueFd Acceptor::bind_address(IpAddress &addr, uint16_t port, bool ipv6_only)
 
     const char *err_str;
 
-    UniqueFd sd(socket(saddr.sa_family, SOCK_STREAM, 0));
+    UniqueFd sd(socket(saddr->sa_family, SOCK_STREAM, 0));
     if (!sd) {
         ipx_strerror(errno, err_str);
         throw std::runtime_error("Failed to create socket: " + std::string(err_str));
@@ -128,7 +135,7 @@ UniqueFd Acceptor::bind_address(IpAddress &addr, uint16_t port, bool ipv6_only)
     std::array<char, INET6_ADDRSTRLEN> addr_str{};
     inet_ntop(static_cast<int>(addr.version), &addr.v6, addr_str.begin(), INET6_ADDRSTRLEN);
 
-    if (bind(sd.get(), &saddr, addr_len) == -1) {
+    if (bind(sd.get(), saddr, addr_len) == -1) {
         ipx_strerror(errno, err_str);
         throw std::runtime_error(
             "Failed to bind to socket (local IP: "