auth: Fix buffer overflow in afsconf_Open

If we fallback to the .AFSCONF file in the user's homedirectory,
the results of getenv("HOME") are copied into a fixed length string,
without checking for overflows.

Instead of risking this, just use asprintf to dynamically construct
a string, and free it when we are done.

Caught by coverity (#985905)

Change-Id: Id8769ede841165d3ff3104143e55767d550d6f87
Reviewed-on: http://gerrit.openafs.org/9292
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>

diff --git a/src/auth/cellconfig.c b/src/auth/cellconfig.c
index b0f7d39..08cc6be 100644 (file)
--- a/src/auth/cellconfig.c
+++ b/src/auth/cellconfig.c
@@ -461,10 +461,18 @@ afsconf_Open(const char *adir)
                fgets(afs_confdir, 128, fp);
                fclose(fp);
            } else {
-               char pathname[256];
+               char *pathname = NULL;
+
+               asprintf(&pathname, "%s/%s", home_dir, ".AFSCONF");
+               if (pathname == NULL) {
+                   free(tdir);
+                   UNLOCK_GLOBAL_MUTEX;
+                   return (struct afsconf_dir *) 0;
+               }
 
-               sprintf(pathname, "%s/%s", home_dir, ".AFSCONF");
                fp = fopen(pathname, "r");
+               free(pathname);
+
                if (fp == 0) {
                    /* Our last chance is the "/.AFSCONF" file */
                    fp = fopen("/.AFSCONF", "r");