mm/kmemleak: fix possible wrong memory scanning period

This commit contains 3 modifications:

1. Convert the type of jiffies_scan_wait to "unsigned long".

2. Use READ/WRITE_ONCE() for accessing "jiffies_scan_wait".

3. Fix the possible wrong memory scanning period.  If you set a large
   memory scanning period like blow, then the "secs" variable will be
   non-zero, however the value of "jiffies_scan_wait" will be zero.

    echo "scan=0x10000000" > /sys/kernel/debug/kmemleak

It is because the type of the msecs_to_jiffies()'s parameter is "unsigned
int", and the "secs * 1000" is larger than its max value.  This in turn
leads a unexpected jiffies_scan_wait, maybe zero.  We corret it by
replacing kstrtoul() with kstrtouint(), and check the msecs to prevent it
larger than UINT_MAX.

Link: https://lkml.kernel.org/r/20210613174022.23044-1-yanfei.xu@windriver.com
Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 92a2d48..228a2fb 100644 (file)
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -219,7 +219,7 @@ static struct task_struct *scan_thread;
 static unsigned long jiffies_min_age;
 static unsigned long jiffies_last_scan;
 /* delay between automatic memory scannings */
-static signed long jiffies_scan_wait;
+static unsigned long jiffies_scan_wait;
 /* enables or disables the task stacks scanning */
 static int kmemleak_stack_scan = 1;
 /* protects the memory scanning, parameters and debug/kmemleak file access */
@@ -1567,7 +1567,7 @@ static int kmemleak_scan_thread(void *arg)
        }
 
        while (!kthread_should_stop()) {
-               signed long timeout = jiffies_scan_wait;
+               signed long timeout = READ_ONCE(jiffies_scan_wait);
 
                mutex_lock(&scan_mutex);
                kmemleak_scan();
@@ -1807,14 +1807,20 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
        else if (strncmp(buf, "scan=off", 8) == 0)
                stop_scan_thread();
        else if (strncmp(buf, "scan=", 5) == 0) {
-               unsigned long secs;
+               unsigned secs;
+               unsigned long msecs;
 
-               ret = kstrtoul(buf + 5, 0, &secs);
+               ret = kstrtouint(buf + 5, 0, &secs);
                if (ret < 0)
                        goto out;
+
+               msecs = secs * MSEC_PER_SEC;
+               if (msecs > UINT_MAX)
+                       msecs = UINT_MAX;
+
                stop_scan_thread();
-               if (secs) {
-                       jiffies_scan_wait = msecs_to_jiffies(secs * 1000);
+               if (msecs) {
+                       WRITE_ONCE(jiffies_scan_wait, msecs_to_jiffies(msecs));
                        start_scan_thread();
                }
        } else if (strncmp(buf, "scan", 4) == 0)