major improvements to temp file name generator

use current time in nanoseconds and some potentially-random (if aslr
is enabled) pointer values for the initial tempfile name generation,
and step via a cheap linear prng on collisions. limit the number of
retry attempts to prevent denial of service attacks even if an
attacker can guess the filenames.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/temp/mkstemp.c b/src/temp/mkstemp.c
index 34642569..2ab3020b 100644
--- a/src/temp/mkstemp.c
+++ b/src/temp/mkstemp.c
@@ -11,8 +11,8 @@ char *__mktemp(char *);
 
 int mkstemp(char *template)
 {
-	int fd;
-	for (;;) {
+	int fd, retries = 100;
+	while (retries--) {
 		if (!__mktemp(template)) return 0;
 		if ((fd = open(template, O_RDWR | O_CREAT | O_EXCL, 0600))>=0)
 			return fd;
@@ -21,6 +21,7 @@ int mkstemp(char *template)
 		 * that we have a valid template string */
 		strcpy(template+strlen(template)-6, "XXXXXX");
 	}
+	return -1;
 }
 
 LFS64(mkstemp);