sftp: fix segfault regression introduced by #4747

This fix adds a defensive check for the case where the char *name in
struct libssh2_knownhost is NULL

Fixes #5041
Closes #5062

1 files changed, 25 insertions, 16 deletions

diff --git a/lib/vssh/libssh2.c b/lib/vssh/libssh2.c
index 8e043747e..c487ccabb 100644
--- a/lib/vssh/libssh2.c
+++ b/lib/vssh/libssh2.c
@@ -694,31 +694,40 @@ static CURLcode ssh_force_knownhost_key_type(struct connectdata *conn)
     while(!libssh2_knownhost_get(sshc->kh, &store, store)) {
       /* For non-standard ports, the name will be enclosed in */
       /* square brackets, followed by a colon and the port */
-      if(store->name[0] == '[') {
-        kh_name_end = strstr(store->name, "]:");
-        if(!kh_name_end) {
-          infof(data, "Invalid host pattern %s in %s\n",
-                store->name, data->set.str[STRING_SSH_KNOWNHOSTS]);
-          continue;
-        }
-        port = atoi(kh_name_end + 2);
-        if(kh_name_end && (port == conn->remote_port)) {
-          kh_name_size = strlen(store->name) - 1 - strlen(kh_name_end);
-          if(strncmp(store->name + 1, conn->host.name, kh_name_size) == 0) {
+      if(store) {
+        if(store->name) {
+          if(store->name[0] == '[') {
+            kh_name_end = strstr(store->name, "]:");
+            if(!kh_name_end) {
+              infof(data, "Invalid host pattern %s in %s\n",
+                    store->name, data->set.str[STRING_SSH_KNOWNHOSTS]);
+              continue;
+            }
+            port = atoi(kh_name_end + 2);
+            if(kh_name_end && (port == conn->remote_port)) {
+              kh_name_size = strlen(store->name) - 1 - strlen(kh_name_end);
+              if(strncmp(store->name + 1,
+                 conn->host.name, kh_name_size) == 0) {
+                found = true;
+                break;
+              }
+            }
+          }
+          else if(strcmp(store->name, conn->host.name) == 0) {
             found = true;
             break;
           }
         }
-      }
-      else if(strcmp(store->name, conn->host.name) == 0) {
-        found = true;
-        break;
+        else {
+          found = true;
+          break;
+        }
       }
     }
 
     if(found) {
       infof(data, "Found host %s in %s\n",
-            store->name, data->set.str[STRING_SSH_KNOWNHOSTS]);
+            conn->host.name, data->set.str[STRING_SSH_KNOWNHOSTS]);
 
       switch(store->typemask & LIBSSH2_KNOWNHOST_KEY_MASK) {
 #ifdef LIBSSH2_KNOWNHOST_KEY_ED25519