PM / devfreq: Fix buffer overflow in trans_stat_show

commit 08e23d05fa6dc4fc13da0ccf09defdd4bbc92ff4 upstream.

Fix buffer overflow in trans_stat_show().

Convert simple snprintf to the more secure scnprintf with size of
PAGE_SIZE.

Add condition checking if we are exceeding PAGE_SIZE and exit early from
loop. Also add at the end a warning that we exceeded PAGE_SIZE and that
stats is disabled.

Return -EFBIG in the case where we don't have enough space to write the
full transition table.

Also document in the ABI that this function can return -EFBIG error.

Link: https://lore.kernel.org/all/20231024183016.14648-2-ansuelsmth@gmail.com/
Cc: stable@vger.kernel.org
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218041
Fixes: e552bbaf5b98 ("PM / devfreq: Add sysfs node for representing frequency transition information.")
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
index 5e6b74f..1e7e0bb 100644 (file)
--- a/Documentation/ABI/testing/sysfs-class-devfreq
+++ b/Documentation/ABI/testing/sysfs-class-devfreq
@@ -52,6 +52,9 @@ Description:
 
                        echo 0 > /sys/class/devfreq/.../trans_stat
 
+               If the transition table is bigger than PAGE_SIZE, reading
+               this will return an -EFBIG error.
+
 What:          /sys/class/devfreq/.../available_frequencies
 Date:          October 2012
 Contact:       Nishanth Menon <nm@ti.com>

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 474d818..81d9df8 100644 (file)
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -1688,7 +1688,7 @@ static ssize_t trans_stat_show(struct device *dev,
                               struct device_attribute *attr, char *buf)
 {
        struct devfreq *df = to_devfreq(dev);
-       ssize_t len;
+       ssize_t len = 0;
        int i, j;
        unsigned int max_state;
 
@@ -1697,7 +1697,7 @@ static ssize_t trans_stat_show(struct device *dev,
        max_state = df->max_state;
 
        if (max_state == 0)
-               return sprintf(buf, "Not Supported.\n");
+               return scnprintf(buf, PAGE_SIZE, "Not Supported.\n");
 
        mutex_lock(&df->lock);
        if (!df->stop_polling &&
@@ -1707,31 +1707,52 @@ static ssize_t trans_stat_show(struct device *dev,
        }
        mutex_unlock(&df->lock);
 
-       len = sprintf(buf, "     From  :   To\n");
-       len += sprintf(buf + len, "           :");
-       for (i = 0; i < max_state; i++)
-               len += sprintf(buf + len, "%10lu",
-                               df->freq_table[i]);
+       len += scnprintf(buf + len, PAGE_SIZE - len, "     From  :   To\n");
+       len += scnprintf(buf + len, PAGE_SIZE - len, "           :");
+       for (i = 0; i < max_state; i++) {
+               if (len >= PAGE_SIZE - 1)
+                       break;
+               len += scnprintf(buf + len, PAGE_SIZE - len, "%10lu",
+                                df->freq_table[i]);
+       }
+       if (len >= PAGE_SIZE - 1)
+               return PAGE_SIZE - 1;
 
-       len += sprintf(buf + len, "   time(ms)\n");
+       len += scnprintf(buf + len, PAGE_SIZE - len, "   time(ms)\n");
 
        for (i = 0; i < max_state; i++) {
+               if (len >= PAGE_SIZE - 1)
+                       break;
                if (df->freq_table[i] == df->previous_freq)
-                       len += sprintf(buf + len, "*");
+                       len += scnprintf(buf + len, PAGE_SIZE - len, "*");
                else
-                       len += sprintf(buf + len, " ");
+                       len += scnprintf(buf + len, PAGE_SIZE - len, " ");
+               if (len >= PAGE_SIZE - 1)
+                       break;
+
+               len += scnprintf(buf + len, PAGE_SIZE - len, "%10lu:",
+                                df->freq_table[i]);
+               for (j = 0; j < max_state; j++) {
+                       if (len >= PAGE_SIZE - 1)
+                               break;
+                       len += scnprintf(buf + len, PAGE_SIZE - len, "%10u",
+                                        df->stats.trans_table[(i * max_state) + j]);
+               }
+               if (len >= PAGE_SIZE - 1)
+                       break;
+               len += scnprintf(buf + len, PAGE_SIZE - len, "%10llu\n", (u64)
+                                jiffies64_to_msecs(df->stats.time_in_state[i]));
+       }
 
-               len += sprintf(buf + len, "%10lu:", df->freq_table[i]);
-               for (j = 0; j < max_state; j++)
-                       len += sprintf(buf + len, "%10u",
-                               df->stats.trans_table[(i * max_state) + j]);
+       if (len < PAGE_SIZE - 1)
+               len += scnprintf(buf + len, PAGE_SIZE - len, "Total transition : %u\n",
+                                df->stats.total_trans);
 
-               len += sprintf(buf + len, "%10llu\n", (u64)
-                       jiffies64_to_msecs(df->stats.time_in_state[i]));
+       if (len >= PAGE_SIZE - 1) {
+               pr_warn_once("devfreq transition table exceeds PAGE_SIZE. Disabling\n");
+               return -EFBIG;
        }
 
-       len += sprintf(buf + len, "Total transition : %u\n",
-                                       df->stats.total_trans);
        return len;
 }