[PATCH 5.10 113/138] PM / devfreq: Fix buffer overflow in trans_stat_show

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christian Marangi <ansuelsmth@gmail.com>

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: Sasha Levin <sashal@kernel.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 Documentation/ABI/testing/sysfs-class-devfreq |    3 +
 drivers/devfreq/devfreq.c                     |   59 +++++++++++++++++---------
 2 files changed, 43 insertions(+), 19 deletions(-)

--- a/Documentation/ABI/testing/sysfs-class-devfreq
+++ b/Documentation/ABI/testing/sysfs-class-devfreq
@@ -66,6 +66,9 @@ 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/.../userspace/set_freq
 Date:		September 2011
 Contact:	MyungJoo Ham <myungjoo.ham@samsung.com>
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -1639,7 +1639,7 @@ static ssize_t trans_stat_show(struct de
 			       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;
 
@@ -1648,7 +1648,7 @@ static ssize_t trans_stat_show(struct de
 	max_state = df->profile->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 &&
@@ -1658,33 +1658,54 @@ static ssize_t trans_stat_show(struct de
 	}
 	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->profile->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->profile->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->profile->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, " ");
 		}
-		len += sprintf(buf + len, "%10lu:",
-				df->profile->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)
+			break;
+
+		len += scnprintf(buf + len, PAGE_SIZE - len, "%10lu:",
+				 df->profile->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, "%10llu\n", (u64)
-			jiffies64_to_msecs(df->stats.time_in_state[i]));
+	if (len < PAGE_SIZE - 1)
+		len += scnprintf(buf + len, PAGE_SIZE - len, "Total transition : %u\n",
+				 df->stats.total_trans);
+
+	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;
 }