libpq: Fix minor TOCTOU violation

petere · petere · commit e882bcae032d · 2024-08-16T06:41:17.000+02:00
libpq checks the permissions of the password file before opening it. The way this is done in two separate operations, a static analyzer would flag as a time-of-check-time-of-use violation. In practice, you can't do anything with that, but it still seems better style to fix it. To fix it, open the file first and then check the permissions on the opened file handle. Reviewed-by: Aleksander Alekseev <aleksander@timescale.com> Reviewed-by: Andreas Karlsson <andreas@proxel.se> Discussion: https://www.postgresql.org/message-id/flat/a3356054-14ae-4e7a-acc6-249d19dac20b%40eisentraut.org
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
@@ -7452,7 +7452,9 @@ passwordFromFile(const char *hostname, const char *port, const char *dbname,
 				 const char *username, const char *pgpassfile)
 {
 	FILE	   *fp;
+#ifndef WIN32
 	struct stat stat_buf;
+#endif
 	PQExpBufferData buf;
 
 	if (dbname == NULL || dbname[0] == '\0')
@@ -7477,10 +7479,14 @@ passwordFromFile(const char *hostname, const char *port, const char *dbname,
 		port = DEF_PGPORT_STR;
 
 	/* If password file cannot be opened, ignore it. */
-	if (stat(pgpassfile, &stat_buf) != 0)
+	fp = fopen(pgpassfile, "r");
+	if (fp == NULL)
 		return NULL;
 
 #ifndef WIN32
+	if (fstat(fileno(fp), &stat_buf) != 0)
+		return NULL;
+
 	if (!S_ISREG(stat_buf.st_mode))
 	{
 		fprintf(stderr,
@@ -7505,10 +7511,6 @@ passwordFromFile(const char *hostname, const char *port, const char *dbname,
 	 */
 #endif
 
-	fp = fopen(pgpassfile, "r");
-	if (fp == NULL)
-		return NULL;
-
 	/* Use an expansible buffer to accommodate any reasonable line length */
 	initPQExpBuffer(&buf);
 
