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authorRich Felker <dalias@aerifal.cx>2011-02-18 17:04:56 -0500
committerRich Felker <dalias@aerifal.cx>2011-02-18 17:04:56 -0500
commit446b4207cc7a30d8a4d5b2445a5a1b27d440f55d (patch)
tree3bc2e2969267d28e3c5b841c25e025afbb1623d4 /src
parent3e9e30166f22f8fb0d5664500bb52a00d1a3c6a3 (diff)
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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.
Diffstat (limited to 'src')
-rw-r--r--src/temp/mkdtemp.c4
-rw-r--r--src/temp/mkstemp.c5
-rw-r--r--src/temp/mktemp.c28
3 files changed, 21 insertions, 16 deletions
diff --git a/src/temp/mkdtemp.c b/src/temp/mkdtemp.c
index 162d98b0..f2ecc510 100644
--- a/src/temp/mkdtemp.c
+++ b/src/temp/mkdtemp.c
@@ -12,7 +12,8 @@ char *__mktemp(char *);
char *mkdtemp(char *template)
{
- for (;;) {
+ int retries = 100;
+ while (retries--) {
if (!__mktemp(template)) return 0;
if (!mkdir(template, 0700)) return template;
if (errno != EEXIST) return 0;
@@ -20,4 +21,5 @@ char *mkdtemp(char *template)
* that we have a valid template string */
strcpy(template+strlen(template)-6, "XXXXXX");
}
+ return 0;
}
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);
diff --git a/src/temp/mktemp.c b/src/temp/mktemp.c
index 1078b9df..1462a16c 100644
--- a/src/temp/mktemp.c
+++ b/src/temp/mktemp.c
@@ -4,28 +4,30 @@
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
+#include <time.h>
+#include <stdint.h>
#include "libc.h"
char *__mktemp(char *template)
{
- static int lock;
- static int index;
- int l = strlen(template);
+ struct timespec ts;
+ size_t l = strlen(template);
+ int retries = 10000;
+ unsigned long r;
if (l < 6 || strcmp(template+l-6, "XXXXXX")) {
errno = EINVAL;
- return NULL;
+ return 0;
}
- LOCK(&lock);
- for (; index < 1000000; index++) {
- snprintf(template+l-6, 6, "%06d", index);
- if (access(template, F_OK) != 0) {
- UNLOCK(&lock);
- return template;
- }
+ clock_gettime(CLOCK_REALTIME, &ts);
+ r = ts.tv_nsec + (uintptr_t)&ts / 16 + (uintptr_t)template;
+ while (retries--) {
+ snprintf(template+l-6, 7, "%06lX", r & 0xffffff);
+ if (access(template, F_OK) < 0) return template;
+ r = r * 1103515245 + 12345;
}
- UNLOCK(&lock);
- return NULL;
+ errno = EEXIST;
+ return 0;
}
weak_alias(__mktemp, mktemp);