session: sanity check public API arguments

Closes #2346

docs/libssh2_session_banner_set.md

@@ -42,6 +42,8 @@ number, it is not really a failure per se.
 # ERRORS
 
 *LIBSSH2_ERROR_ALLOC* - An internal memory allocation call failed.
+*LIBSSH2_ERROR_BAD_USE* - If `session` is NULL.
+*LIBSSH2_ERROR_OUT_OF_BOUNDARY* - If banner is oversized (\> 4 MiB).
 
 # AVAILABILITY
 

docs/libssh2_session_callback_set.md

@@ -37,4 +37,4 @@ which is expecting and returning a function pointer.
 # RETURN VALUE
 
 Pointer to previous callback handler. Returns NULL if no prior callback
-handler was set or the callback type was unknown.
+handler was set, the callback type was unknown, or `session` is NULL.

docs/libssh2_session_callback_set2.md

@@ -168,4 +168,4 @@ can call libssh2_agent_sign(3) to perform signing.
 # RETURN VALUE
 
 Pointer to previous callback handler. Returns NULL if no prior callback
-handler was set or the callback type was unknown.
+handler was set, the callback type was unknown, or `session` is NULL.

docs/libssh2_session_handshake.md

@@ -38,6 +38,8 @@ Returns 0 on success, negative on failure.
 
 # ERRORS
 
+*LIBSSH2_ERROR_BAD_USE* - If `session` is NULL.
+
 *LIBSSH2_ERROR_SOCKET_NONE* - The socket is invalid.
 
 *LIBSSH2_ERROR_BANNER_SEND* - Unable to send banner to remote host.

docs/libssh2_session_method_pref.md

@@ -45,6 +45,8 @@ LIBSSH2_ERROR_EAGAIN is a negative number, it is not really a failure per se.
 
 # ERRORS
 
+*LIBSSH2_ERROR_BAD_USE* - If `session` or `prefs` are NULL.
+
 *LIBSSH2_ERROR_INVAL* - The requested method type was invalid.
 
 *LIBSSH2_ERROR_ALLOC* - An internal memory allocation call failed.

src/kex.c

@@ -3773,9 +3773,14 @@ int libssh2_session_method_pref(LIBSSH2_SESSION *session, int method_type,
 {
     char **prefvar, *s, *newprefs;
     char *tmpprefs = NULL;
-    size_t prefs_len = strlen(prefs);
+    size_t prefs_len;
     const struct common_method **mlist;
 
+    if(!session || !prefs)
+        return LIBSSH2_ERROR_BAD_USE;
+
+    prefs_len = strlen(prefs);
+
     switch(method_type) {
     case LIBSSH2_METHOD_KEX:
         prefvar = &session->kex_prefs;

src/session.c

@@ -335,12 +335,20 @@ static int session_get_socket_nonblocking(libssh2_socket_t sockfd)
  */
 int libssh2_session_banner_set(LIBSSH2_SESSION *session, const char *banner)
 {
-    size_t banner_len = banner ? strlen(banner) : 0;
+    size_t banner_len;
+
+    if(!session)
+        return LIBSSH2_ERROR_BAD_USE;
+
+    banner_len = banner ? strlen(banner) : 0;
+
+    if(banner_len > (4 * 1024 * 1024))
+        return LIBSSH2_ERROR_OUT_OF_BOUNDARY;
 
     if(session->local.banner)
         SSH2_SAFEFREE(session, session->local.banner);
 
-    if(!banner_len)
+    if(!banner || !banner_len)
         return 0;
 
     session->local.banner = SSH2_ALLOC(session, banner_len + 3);
@@ -433,6 +441,9 @@ libssh2_cb_generic *libssh2_session_callback_set2(LIBSSH2_SESSION *session,
 {
     libssh2_cb_generic *oldcb;
 
+    if(!session)
+        return NULL;
+
     switch(cbtype) {
     case LIBSSH2_CALLBACK_IGNORE:
         oldcb = (libssh2_cb_generic *)session->ssh_msg_ignore;
@@ -792,6 +803,9 @@ int libssh2_session_handshake(LIBSSH2_SESSION *session, libssh2_socket_t sock)
 {
     int rc;
 
+    if(!session)
+        return LIBSSH2_ERROR_BAD_USE;
+
     BLOCK_ADJUST(rc, session, session_startup(session, sock));
 
     return rc;
@@ -1032,6 +1046,9 @@ int libssh2_session_free(LIBSSH2_SESSION *session)
 {
     int rc;
 
+    if(!session)
+        return LIBSSH2_ERROR_BAD_USE;
+
     BLOCK_ADJUST(rc, session, session_free(session));
 
     return rc;
@@ -1093,6 +1110,10 @@ int libssh2_session_disconnect_ex(LIBSSH2_SESSION *session, int reason,
                                   const char *description, const char *lang)
 {
     int rc;
+
+    if(!session)
+        return LIBSSH2_ERROR_BAD_USE;
+
     session->state &= ~SSH2_STATE_INITIAL_KEX;
     session->state &= ~SSH2_STATE_EXCHANGING_KEYS;
     BLOCK_ADJUST(rc, session,
@@ -1112,6 +1133,9 @@ const char *libssh2_session_methods(LIBSSH2_SESSION *session, int method_type)
     /* All methods have char *name as their first element */
     const struct kex_method *method = NULL;
 
+    if(!session)
+        return NULL;
+
     switch(method_type) {
     case LIBSSH2_METHOD_KEX:
         method = session->kex;
@@ -1170,6 +1194,9 @@ const char *libssh2_session_methods(LIBSSH2_SESSION *session, int method_type)
  */
 void **libssh2_session_abstract(LIBSSH2_SESSION *session)
 {
+    if(!session)
+        return NULL;
+
     return &session->abstract;
 }
 
@@ -1183,6 +1210,9 @@ int libssh2_session_last_error(LIBSSH2_SESSION *session, char **errmsg,
 {
     size_t msglen = 0;
 
+    if(!session)
+        return LIBSSH2_ERROR_BAD_USE;
+
     /* No error to report */
     if(!session->err_code) {
         if(errmsg) {
@@ -1227,6 +1257,9 @@ int libssh2_session_last_error(LIBSSH2_SESSION *session, char **errmsg,
  */
 int libssh2_session_last_errno(LIBSSH2_SESSION *session)
 {
+    if(!session)
+        return LIBSSH2_ERROR_BAD_USE;
+
     return session->err_code;
 }
 
@@ -1250,6 +1283,9 @@ int libssh2_session_set_last_error(LIBSSH2_SESSION *session,
  */
 int libssh2_session_flag(LIBSSH2_SESSION *session, int flag, int value)
 {
+    if(!session)
+        return LIBSSH2_ERROR_BAD_USE;
+
     switch(flag) {
     case LIBSSH2_FLAG_SIGPIPE:
         session->flag.sigpipe = value;
@@ -1288,6 +1324,9 @@ int ssh2_session_set_blocking(LIBSSH2_SESSION *session, int blocking)
  */
 void libssh2_session_set_blocking(LIBSSH2_SESSION *session, int blocking)
 {
+    if(!session)
+        return;
+
     (void)ssh2_session_set_blocking(session, blocking);
 }
 
@@ -1296,6 +1335,9 @@ void libssh2_session_set_blocking(LIBSSH2_SESSION *session, int blocking)
  */
 int libssh2_session_get_blocking(LIBSSH2_SESSION *session)
 {
+    if(!session)
+        return 0;
+
     return session->api_block_mode;
 }
 
@@ -1305,6 +1347,9 @@ int libssh2_session_get_blocking(LIBSSH2_SESSION *session)
  */
 void libssh2_session_set_timeout(LIBSSH2_SESSION *session, long timeout)
 {
+    if(!session)
+        return;
+
     session->api_timeout = timeout;
 }
 
@@ -1313,6 +1358,9 @@ void libssh2_session_set_timeout(LIBSSH2_SESSION *session, long timeout)
  */
 long libssh2_session_get_timeout(LIBSSH2_SESSION *session)
 {
+    if(!session)
+        return 0;
+
     return session->api_timeout;
 }
 
@@ -1322,6 +1370,9 @@ long libssh2_session_get_timeout(LIBSSH2_SESSION *session)
  */
 void libssh2_session_set_read_timeout(LIBSSH2_SESSION *session, long timeout)
 {
+    if(!session)
+        return;
+
     if(timeout <= 0)
         timeout = SSH2_DEFAULT_READ_TIMEOUT;
 
@@ -1333,6 +1384,9 @@ void libssh2_session_set_read_timeout(LIBSSH2_SESSION *session, long timeout)
  */
 long libssh2_session_get_read_timeout(LIBSSH2_SESSION *session)
 {
+    if(!session)
+        return 0;
+
     return session->packet_read_timeout;
 }
 
@@ -1730,6 +1784,9 @@ int libssh2_poll(LIBSSH2_POLLFD *fds, unsigned int nfds, long timeout)
  */
 int libssh2_session_block_directions(LIBSSH2_SESSION *session)
 {
+    if(!session)
+        return 0;
+
     return session->socket_block_directions;
 }
 
@@ -1738,7 +1795,7 @@ int libssh2_session_block_directions(LIBSSH2_SESSION *session)
  */
 const char *libssh2_session_banner_get(LIBSSH2_SESSION *session)
 {
-    if(!session)  /* to avoid a coredump when session is NULL */
+    if(!session)
         return NULL;
 
     if(!session->remote.banner)