Hello,

Hello Daniel,

thanks for the notice of the buffer length - will fix it and test again.

The report from the tool mentioned that it is an issue also for multi-process, but of course more critical for multi-threaded:

"The time related functions such as gmtime fill data into a tm struct or char array in shared memory and then returns a pointer to that memory. If the function is called from multiple places in the same program, and especially if it is called from multiple threads in the same program, then the calls will overwrite each other's data."

Therefore I think that it is definitely safer, especially as there might be libraries that use it as well, that we don't see.

When is single process, not multi-threading, there can be an issue when keeping a global variable with the result of ctime() (and the other functions) and using it later expecting the same result, while in between the executed code could have been used the same function.

But in the functions you did the change, there were local operations within the scope of the functions and the result of the time-related functions was copied. There is no other function from other library executed that could overwrite the value.

Anyhow, in the current Kamailio architecture is not making anything safer compared with the old variant. Maybe for the future were multi-threading is added to some extent. Overall I am fine with the change, just wanted to be sure was like a cosmetic change, not something that created problems.

Cheers,
Daniel

We probably don't need to backport it, thought.

Cheers,

Henning

Am 20.09.19 um 11:03 schrieb Daniel-Constantin Mierla:

Hello,

were these changes to use ctime_r() (and in other commits gmtime_r(),
localtime_r(), asctime_r()) required to fix existing issues or more like
a preference to use them? Because Kamailio is multiprocess and thread
safety should not be a concern, otherwise there might be a lot of other
place to take care of thread safety...

Anyhow, there are out of bound writes introduced as the buffers must be
at least 26 chars long, not 25 -- those need to be fixed.

Cheers,
Daniel

On 20.09.19 00:04, Henning Westerholt wrote:

Module: kamailio
Branch: master
Commit: dc2acb895538131e99c770da6f7448cb5a46fc32
URL: https://github.com/kamailio/kamailio/commit/dc2acb895538131e99c770da6f7448cb5a46fc32

Author: Henning Westerholt <hw@skalatan.de>
Committer: Henning Westerholt <hw@skalatan.de>
Date: 2019-09-19T23:49:32+02:00

core: replace glibc time function calls with the thread-safe versions

- replace glibc time function calls with the thread-safe versions, to prevent
  race conditions from multi-process / multi-threaded access
- used in 'kamcmd core.uptime' rpc cmd, no functional change, locally tested

---

Modified: src/core/core_cmd.c

---

Diff:  https://github.com/kamailio/kamailio/commit/dc2acb895538131e99c770da6f7448cb5a46fc32.diff
Patch: https://github.com/kamailio/kamailio/commit/dc2acb895538131e99c770da6f7448cb5a46fc32.patch

---

diff --git a/src/core/core_cmd.c b/src/core/core_cmd.c
index 5b1c4624ed..717e240fde 100644
--- a/src/core/core_cmd.c
+++ b/src/core/core_cmd.c
@@ -224,8 +224,7 @@ static const char* dst_blst_stats_get_doc[] = {
 #endif
 
 
-
-#define MAX_CTIME_LEN 128
+#define MAX_CTIME_LEN 25
 
 /* up time */
 static char up_since_ctime[MAX_CTIME_LEN];
@@ -381,13 +380,14 @@ static void core_uptime(rpc_t* rpc, void* c)
 {
 	void* s;
 	time_t now;
+	char buf[MAX_CTIME_LEN];
 	str snow;
+	snow.s = buf;
 
 	time(&now);
 
 	if (rpc->add(c, "{", &s) < 0) return;
-	snow.s = ctime(&now);
-	if(snow.s) {
+	if(ctime_r(&now, snow.s)) {
 		snow.len = strlen(snow.s);
 		if(snow.len>2 && snow.s[snow.len-1]=='\n') snow.len--;
 		rpc->struct_add(s, "S", "now", &snow);
@@ -1187,21 +1187,14 @@ int register_core_rpcs(void)
 
 int rpc_init_time(void)
 {
-	char *t;
-	t=ctime(&up_since);
-	if (strlen(t)+1>=MAX_CTIME_LEN) {
-		ERR("Too long data %d\n", (int)strlen(t));
+	char t[MAX_CTIME_LEN];
+	int len;
+	if (! ctime_r(&up_since, t)) {
+		ERR("Invalid time value\n");
 		return -1;
 	}
 	strcpy(up_since_ctime, t);
-	t = up_since_ctime + strlen(up_since_ctime);
-	while(t>up_since_ctime) {
-		if(*t=='\0' || *t=='\r' || *t=='\n') {
-			*t = '\0';
-		} else {
-			break;
-		}
-		t--;
-	}
+	len = strlen(up_since_ctime);
+	if(len>2 && up_since_ctime[len-1]=='\n') up_since_ctime[len-1]='\0';
 	return 0;
 }


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-- 
Daniel-Constantin Mierla -- www.asipto.com
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