[PATCH] Fix 100% CPU usage (again) due to log rotate

[PATCH] Fix 100% CPU usage (again) due to log rotate

[Steven Rostedt (VMware)]

If the num_logs is set to 0 and keep_logs is set, we go back into a
loop of MAX_INT! in rotate_logs().

commit 9145e97c ("Do not rotate logs when num_logs < 2.") fixed the
issue with not going further if num_logs is less than 2, because if
num_logs is zero, we trigger this bug because of the loop:

  for (i=num_logs - 1; i>1; i--) {

As i is an unsigned int, if num_logs is zero, we initialize i to
"0 - 1" or 4,294,967,295. Thus, runs this loop over 4 billion times!

But this caused a regressing if keep_logs is set, so this
num_logs < 2 was skipped if keep_logs is set, causing the huge loop
to run once again if num_logs is zero!

There's no reason i needs to be unsigned, if i is signed, then if we
pass in num_logs = 0, then i will start off as -1, and -1 > 1 will fail
the loop and fix the issue. I don't envision anyone wanting to
keep 2,147,483,648 log files around.

Fixes: a7f9f8b5 ("Fix auditd regression where keep_logs is limited by rotate_logs 2 file test")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
diff --git a/src/auditd-event.c b/src/auditd-event.c
index 1c93173..68eacd5 100644
--- a/src/auditd-event.c
+++ b/src/auditd-event.c
@@ -1012,8 +1012,8 @@ static void fix_disk_permissions(void)
  
 static void rotate_logs(unsigned int num_logs, unsigned int keep_logs)
 {
-	int rc;
-	unsigned int len, i;
+	int rc, i;
+	unsigned int len;
 	char *oldname, *newname;
 
 	/* Check that log rotation is enabled in the configuration file. There
@@ -1065,7 +1065,7 @@ static void rotate_logs(unsigned int num_logs, unsigned int keep_logs)
 		snprintf(oldname, len, "%s.1", config->log_file);
 
 	known_logs = 0;
-	for (i=num_logs - 1; i>1; i--) {
+	for (i=(int)num_logs - 1; i>1; i--) {
 		snprintf(oldname, len, "%s.%u", config->log_file, i-1);
 		snprintf(newname, len, "%s.%u", config->log_file, i);
 		/* if the old file exists */

Re: [PATCH] Fix 100% CPU usage (again) due to log rotate

[Steve Grubb]

On Fri, 25 Oct 2019 15:37:09 -0400
"Steven Rostedt (VMware)" <rostedt@goodmis.org> wrote:

> If the num_logs is set to 0 and keep_logs is set, we go back into a
> loop of MAX_INT! in rotate_logs().

Thanks. Applied.

-Steve

> commit 9145e97c ("Do not rotate logs when num_logs < 2.") fixed the
> issue with not going further if num_logs is less than 2, because if
> num_logs is zero, we trigger this bug because of the loop:
> 
>   for (i=num_logs - 1; i>1; i--) {
> 
> As i is an unsigned int, if num_logs is zero, we initialize i to
> "0 - 1" or 4,294,967,295. Thus, runs this loop over 4 billion times!
> 
> But this caused a regressing if keep_logs is set, so this
> num_logs < 2 was skipped if keep_logs is set, causing the huge loop
> to run once again if num_logs is zero!
> 
> There's no reason i needs to be unsigned, if i is signed, then if we
> pass in num_logs = 0, then i will start off as -1, and -1 > 1 will
> fail the loop and fix the issue. I don't envision anyone wanting to
> keep 2,147,483,648 log files around.
> 
> Fixes: a7f9f8b5 ("Fix auditd regression where keep_logs is limited by
> rotate_logs 2 file test") Signed-off-by: Steven Rostedt (VMware)
> <rostedt@goodmis.org> ---
> diff --git a/src/auditd-event.c b/src/auditd-event.c
> index 1c93173..68eacd5 100644
> --- a/src/auditd-event.c
> +++ b/src/auditd-event.c
> @@ -1012,8 +1012,8 @@ static void fix_disk_permissions(void)
>   
>  static void rotate_logs(unsigned int num_logs, unsigned int
> keep_logs) {
> -	int rc;
> -	unsigned int len, i;
> +	int rc, i;
> +	unsigned int len;
>  	char *oldname, *newname;
>  
>  	/* Check that log rotation is enabled in the configuration
> file. There @@ -1065,7 +1065,7 @@ static void rotate_logs(unsigned
> int num_logs, unsigned int keep_logs) snprintf(oldname, len, "%s.1",
> config->log_file); 
>  	known_logs = 0;
> -	for (i=num_logs - 1; i>1; i--) {
> +	for (i=(int)num_logs - 1; i>1; i--) {
>  		snprintf(oldname, len, "%s.%u", config->log_file,
> i-1); snprintf(newname, len, "%s.%u", config->log_file, i);
>  		/* if the old file exists */