CVE-2025-4878 Initialize pointers where possible

This is mostly mechanical change initializing all the pointers I was able to
find with some grep and manual review of sources and examples.

Used the following greps (which yield some false positives though):

    git grep "    \w* *\* *\w*;$"
    git grep " ssh_session \w*;"
    git grep " ssh_channel \w*;"
    git grep " struct ssh_iterator \*\w*;"
    git grep " ssh_bind \w*;"
    git grep " ssh_key \w*;"
    git grep " ssh_string \w*;"
    git grep " ssh_buffer \w*;"
    git grep " HMACCTX \w*;"
    git grep " SHACTX \w*;"
    grep -rinP '^(?!.*=)\s*(?:\w+\s+)*\w+\s*\*\s*\w+\s*;'

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

doc/authentication.dox

@@ -105,7 +105,7 @@ Here is a small example of password authentication:
 @code
 int authenticate_password(ssh_session session)
 {
-  char *password;
+  char *password = NULL;
   int rc;
 
   password = getpass("Enter your password: ");
@@ -218,7 +218,7 @@ int authenticate_kbdint(ssh_session session)
   rc = ssh_userauth_kbdint(session, NULL, NULL);
   while (rc == SSH_AUTH_INFO)
   {
-    const char *name, *instruction;
+    const char *name = NULL, *instruction = NULL;
     int nprompts, iprompt;
 
     name = ssh_userauth_kbdint_getname(session);
@@ -231,7 +231,7 @@ int authenticate_kbdint(ssh_session session)
       printf("%s\n", instruction);
     for (iprompt = 0; iprompt < nprompts; iprompt++)
     {
-      const char *prompt;
+      const char *prompt = NULL;
       char echo;
 
       prompt = ssh_userauth_kbdint_getprompt(session, iprompt, &echo);
@@ -251,7 +251,7 @@ int authenticate_kbdint(ssh_session session)
       }
       else
       {
-        char *ptr;
+        char *ptr = NULL;
 
         ptr = getpass(prompt);
         if (ssh_userauth_kbdint_setanswer(session, iprompt, ptr) < 0)
@@ -354,7 +354,7 @@ The following example shows how to retrieve and dispose the issue banner:
 int display_banner(ssh_session session)
 {
   int rc;
-  char *banner;
+  char *banner = NULL;
 
 /*
  *** Does not work without calling ssh_userauth_none() first ***

doc/command.dox

@@ -22,7 +22,7 @@ a SSH session that uses this channel:
 @code
 int show_remote_files(ssh_session session)
 {
-  ssh_channel channel;
+  ssh_channel channel = NULL;
   int rc;
 
   channel = ssh_channel_new(session);

doc/forwarding.dox

@@ -100,7 +100,7 @@ used to retrieve google's home page from the remote SSH server.
 @code
 int direct_forwarding(ssh_session session)
 {
-  ssh_channel forwarding_channel;
+  ssh_channel forwarding_channel = NULL;
   int rc = SSH_ERROR;
   char *http_get = "GET / HTTP/1.1\nHost: www.google.com\n\n";
   int nbytes, nwritten;
@@ -161,7 +161,7 @@ local libssh application, which handles them:
 int web_server(ssh_session session)
 {
   int rc;
-  ssh_channel channel;
+  ssh_channel channel = NULL;
   char buffer[256];
   int nbytes, nwritten;
   int port = 0;

doc/guided_tour.dox

@@ -79,7 +79,7 @@ Here is a small example of how to use it:
 
 int main()
 {
-  ssh_session my_ssh_session;
+  ssh_session my_ssh_session = NULL;
   int verbosity = SSH_LOG_PROTOCOL;
   int port = 22;
 
@@ -126,7 +126,7 @@ Here's an example:
 
 int main()
 {
-  ssh_session my_ssh_session;
+  ssh_session my_ssh_session = NULL;
   int rc;
 
   my_ssh_session = ssh_new();
@@ -190,8 +190,8 @@ int verify_knownhost(ssh_session session)
     ssh_key srv_pubkey = NULL;
     size_t hlen;
     char buf[10];
-    char *hexa;
-    char *p;
+    char *hexa = NULL;
+    char *p = NULL;
     int cmp;
     int rc;
 
@@ -317,9 +317,9 @@ The example below shows an authentication with password:
 
 int main()
 {
-  ssh_session my_ssh_session;
+  ssh_session my_ssh_session = NULL;
   int rc;
-  char *password;
+  char *password = NULL;
 
   // Open session and set options
   my_ssh_session = ssh_new();
@@ -380,7 +380,7 @@ The example below shows how to execute a remote command:
 @code
 int show_remote_processes(ssh_session session)
 {
-  ssh_channel channel;
+  ssh_channel channel = NULL;
   int rc;
   char buffer[256];
   int nbytes;

doc/shell.dox

@@ -26,7 +26,7 @@ The code sample below achieves these tasks:
 @code
 int shell_session(ssh_session session)
 {
-  ssh_channel channel;
+  ssh_channel channel = NULL;
   int rc;
 
   channel = ssh_channel_new(session);