cpufreq: stats: Fix buffer overflow detection in trans_stats()

Commit 3c0897c180c6 ("cpufreq: Use scnprintf() for avoiding potential
buffer overflow") switched from snprintf to the more secure scnprintf
but never updated the exit condition for PAGE_SIZE.

As the commit say and as scnprintf document, what scnprintf returns what
is actually written not counting the '\0' end char. This results in the
case of len exceeding the size, len set to PAGE_SIZE - 1, as it can be
written at max PAGE_SIZE - 1 (as '\0' is not counted)

Because of len is never set to PAGE_SIZE, the function never break early,
never prints the warning and never return -EFBIG.

Fix this by changing the condition to PAGE_SIZE - 1 to correctly trigger
the error.

Cc: 5.10+ <stable@vger.kernel.org> # 5.10+
Fixes: 3c0897c180c6 ("cpufreq: Use scnprintf() for avoiding potential buffer overflow")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
index a33df3c66c88c24be2da6285889da216c9fee2a5..40a9ff18da068c278e6e86311ccc8846993af717 100644 (file)
--- a/drivers/cpufreq/cpufreq_stats.c
+++ b/drivers/cpufreq/cpufreq_stats.c
@@ -131,23 +131,23 @@ static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf)
        len += sysfs_emit_at(buf, len, "   From  :    To\n");
        len += sysfs_emit_at(buf, len, "         : ");
        for (i = 0; i < stats->state_num; i++) {
-               if (len >= PAGE_SIZE)
+               if (len >= PAGE_SIZE - 1)
                        break;
                len += sysfs_emit_at(buf, len, "%9u ", stats->freq_table[i]);
        }
-       if (len >= PAGE_SIZE)
-               return PAGE_SIZE;
+       if (len >= PAGE_SIZE - 1)
+               return PAGE_SIZE - 1;
 
        len += sysfs_emit_at(buf, len, "\n");
 
        for (i = 0; i < stats->state_num; i++) {
-               if (len >= PAGE_SIZE)
+               if (len >= PAGE_SIZE - 1)
                        break;
 
                len += sysfs_emit_at(buf, len, "%9u: ", stats->freq_table[i]);
 
                for (j = 0; j < stats->state_num; j++) {
-                       if (len >= PAGE_SIZE)
+                       if (len >= PAGE_SIZE - 1)
                                break;
 
                        if (pending)
@@ -157,12 +157,12 @@ static ssize_t show_trans_table(struct cpufreq_policy *policy, char *buf)
 
                        len += sysfs_emit_at(buf, len, "%9u ", count);
                }
-               if (len >= PAGE_SIZE)
+               if (len >= PAGE_SIZE - 1)
                        break;
                len += sysfs_emit_at(buf, len, "\n");
        }
 
-       if (len >= PAGE_SIZE) {
+       if (len >= PAGE_SIZE - 1) {
                pr_warn_once("cpufreq transition table exceeds PAGE_SIZE. Disabling\n");
                return -EFBIG;
        }