Minor bug fixes for socket.c

While running a static code analysis tool (Parfait) on fetchmail, it found some
bugs:

Error: Memory leak (CWE 401)
   Memory leak of pointer 'plugin_copy' allocated with malloc((plugin_copy_len + 1))
        at line 137 of components/fetchmail/fetchmail-6.3.22/socket.c in function 'parse_plugin'.
          'plugin_copy' allocated at line 107 with malloc((plugin_copy_len + 1)).
          plugin_copy leaks when plugin_copy_offset >= plugin_copy_len at line 114.

Error: Null pointer dereference (CWE 476)
   Read from null pointer 'argvec'
        at line 189 of components/fetchmail/fetchmail-6.3.22/socket.c in function 'handle_plugin'.
          Function 'parse_plugin' may return constant 'NULL' at line 137, called at line 188.
          Null pointer introduced at line 137 in function 'parse_plugin'.
        at line 190 of components/fetchmail/fetchmail-6.3.22/socket.c in function 'handle_plugin'.
          Function 'parse_plugin' may return constant 'NULL' at line 137, called at line 188.
          Null pointer introduced at line 137 in function 'parse_plugin'.

(I realize these are on 6.3.22; I checked and verified that this portion of
the code is the same in 6.3.24.)

The attached patch fixes each of these.

(Note by Matthias Andree:
The NULL pointer dereference fix does not require error reporting,
because parse_plugin() will already have reported the out-of-memory
error that causes the NULL to be returned.)

1 files changed, 3 insertions, 0 deletions

diff --git a/socket.c b/socket.c
index 48201d38..58a8e15e 100644
--- a/socket.c
+++ b/socket.c
@@ -133,6 +133,7 @@ static char *const *parse_plugin(const char *plugin, const char *host, const cha
 	argvec = (char **)malloc(s);
 	if (!argvec)
 	{
+		free(plugin_copy);
 		report(stderr, GT_("fetchmail: malloc failed\n"));
 		return NULL;
 	}
@@ -186,6 +187,8 @@ static int handle_plugin(const char *host,
 		if (outlevel >= O_VERBOSE)
 		    report(stderr, GT_("running %s (host %s service %s)\n"), plugin, host, service);
 		argvec = parse_plugin(plugin,host,service);
+		if (argvec == NULL)
+			_exit(EXIT_FAILURE);
 		execvp(*argvec, argvec);
 		report(stderr, GT_("execvp(%s) failed\n"), *argvec);
 		_exit(EXIT_FAILURE);