pam_xauth: avoid building argv inside run_coprocess

Passing an indeterminate number of arguments via varargs to a function is
dependent on the compiler implementation. Instead, as we are handing off
the argv to execv directly anyway without further processing we can
build this array inline at the call site instead.

Doing so actually also avoids a previous limitation of the old
implementation where long argument lists could have been truncated
silently to their first nine arguments. The new implementation does not
impose such a limit on the caller.

Signed-off-by: Benny Baumann <BenBE@geshi.org>

1 files changed, 8 insertions, 18 deletions

diff --git a/modules/pam_xauth/pam_xauth.c b/modules/pam_xauth/pam_xauth.c
index 9d7369c0..35bc5aeb 100644
--- a/modules/pam_xauth/pam_xauth.c
+++ b/modules/pam_xauth/pam_xauth.c
@@ -87,14 +87,13 @@ static const char * const xauthpaths[] = {
  * given input on stdin, and storing any output it generates. */
 static int
 run_coprocess(pam_handle_t *pamh, const char *input, char **output,
-	      uid_t uid, gid_t gid, const char *command, ...)
+	      uid_t uid, gid_t gid, const char *command, const char *argv[])
 {
 	int ipipe[2], opipe[2], i;
 	char buf[LINE_MAX];
 	pid_t child;
 	char *buffer = NULL;
 	size_t buffer_size = 0;
-	va_list ap;
 	struct sigaction newsa, oldsa;
 
 	*output = NULL;
@@ -134,9 +133,6 @@ run_coprocess(pam_handle_t *pamh, const char *input, char **output,
 	}
 
 	if (child == 0) {
-		/* We're the child. */
-		size_t j;
-		const char *args[10] = {};
 		/* Drop privileges. */
 		if (setgid(gid) == -1)
 		  {
@@ -176,18 +172,9 @@ run_coprocess(pam_handle_t *pamh, const char *input, char **output,
 						    PAM_MODUTIL_NULL_FD) < 0) {
 		    _exit(1);
 		}
-		/* Convert the varargs list into a regular array of strings. */
-		va_start(ap, command);
-		args[0] = command;
-		for (j = 1; j < PAM_ARRAY_SIZE(args) - 1; j++) {
-			args[j] = va_arg(ap, const char*);
-			if (args[j] == NULL) {
-				break;
-			}
-		}
 		/* Run the command. */
 		DIAG_PUSH_IGNORE_CAST_QUAL;
-		execv(command, (char *const *) args);
+		execv(command, (char *const *) argv);
 		DIAG_POP_IGNORE_CAST_QUAL;
 		/* Never reached. */
 		_exit(1);
@@ -550,8 +537,9 @@ pam_sm_open_session (pam_handle_t *pamh, int flags UNUSED,
 	}
 	if (run_coprocess(pamh, NULL, &cookie,
 			  getuid(), getgid(),
+			  xauth, (const char *[]) {
 			  xauth, "-f", cookiefile, "nlist", display,
-			  NULL) == 0) {
+			  NULL}) == 0) {
 #ifdef WITH_SELINUX
 		char *context_raw = NULL;
 #endif
@@ -608,8 +596,9 @@ pam_sm_open_session (pam_handle_t *pamh, int flags UNUSED,
 					}
 					run_coprocess(pamh, NULL, &cookie,
 						      getuid(), getgid(),
+						      xauth, (const char *[]) {
 						      xauth, "-f", cookiefile,
-						      "nlist", t, NULL);
+						      "nlist", t, NULL});
 				}
 				free(t);
 				t = NULL;
@@ -750,7 +739,8 @@ pam_sm_open_session (pam_handle_t *pamh, int flags UNUSED,
 		}
 		run_coprocess(pamh, cookie, &tmp,
 			      tpwd->pw_uid, tpwd->pw_gid,
-			      xauth, "-f", cookiefile, "nmerge", "-", NULL);
+			      xauth, (const char *[]) {
+			      xauth, "-f", cookiefile, "nmerge", "-", NULL});
 
 		/* We don't need to keep a copy of these around any more. */
 		cookiefile = NULL;