From 67c45f41b61503a4e7a27d8321d151275d36fbce Mon Sep 17 00:00:00 2001
From: "Vanya A. Sergeev" <v@sergeev.io>
Date: Fri, 10 Oct 2025 23:28:10 -0500
Subject: [PATCH] gpio: fix null termination of internal buffers in sysfs impl

unlikely to be encountered, but handled correctly now.
---
 src/gpio_sysfs.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/src/gpio_sysfs.c b/src/gpio_sysfs.c
index 83d36ad..42dce66 100644
--- a/src/gpio_sysfs.c
+++ b/src/gpio_sysfs.c
@@ -174,17 +174,17 @@ static int gpio_sysfs_get_direction(gpio_t *gpio, gpio_direction_t *direction) {
     if ((fd = open(gpio_path, O_RDONLY)) < 0)
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errno, "Opening GPIO 'direction'");
 
-    if ((ret = read(fd, buf, sizeof(buf))) < 0) {
+    if ((ret = read(fd, buf, sizeof(buf) - 1)) < 0) {
         int errsv = errno;
         close(fd);
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errsv, "Reading GPIO 'direction'");
     }
 
+    buf[ret] = '\0';
+
     if (close(fd) < 0)
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errno, "Closing GPIO 'direction'");
 
-    buf[ret] = '\0';
-
     if (strcmp(buf, "in\n") == 0)
         *direction = GPIO_DIR_IN;
     else if (strcmp(buf, "out\n") == 0)
@@ -240,17 +240,17 @@ static int gpio_sysfs_get_edge(gpio_t *gpio, gpio_edge_t *edge) {
     if ((fd = open(gpio_path, O_RDONLY)) < 0)
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errno, "Opening GPIO 'edge'");
 
-    if ((ret = read(fd, buf, sizeof(buf))) < 0) {
+    if ((ret = read(fd, buf, sizeof(buf) - 1)) < 0) {
         int errsv = errno;
         close(fd);
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errsv, "Reading GPIO 'edge'");
     }
 
+    buf[ret] = '\0';
+
     if (close(fd) < 0)
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errno, "Closing GPIO 'edge'");
 
-    buf[ret] = '\0';
-
     if (strcmp(buf, "none\n") == 0)
         *edge = GPIO_EDGE_NONE;
     else if (strcmp(buf, "rising\n") == 0)
@@ -339,7 +339,7 @@ static int gpio_sysfs_get_inverted(gpio_t *gpio, bool *inverted) {
     if ((fd = open(gpio_path, O_RDONLY)) < 0)
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errno, "Opening GPIO 'active_low'");
 
-    if ((ret = read(fd, buf, sizeof(buf))) < 0) {
+    if ((ret = read(fd, buf, sizeof(buf) - 1)) < 0) {
         int errsv = errno;
         close(fd);
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errsv, "Reading GPIO 'active_low'");
@@ -348,8 +348,6 @@ static int gpio_sysfs_get_inverted(gpio_t *gpio, bool *inverted) {
     if (close(fd) < 0)
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errno, "Closing GPIO 'active_low'");
 
-    buf[ret] = '\0';
-
     if (buf[0] == '0')
         *inverted = false;
     else if (buf[0] == '1')
@@ -434,17 +432,17 @@ static int gpio_sysfs_chip_label(gpio_t *gpio, char *str, size_t len) {
     if ((fd = open(gpio_path, O_RDONLY)) < 0)
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errno, "Opening GPIO chip 'label'");
 
-    if ((ret = read(fd, str, len)) < 0) {
+    if ((ret = read(fd, str, len - 1)) < 0) {
         int errsv = errno;
         close(fd);
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errsv, "Reading GPIO chip 'label'");
     }
 
+    str[ret] = '\0';
+
     if (close(fd) < 0)
         return _gpio_error(gpio, GPIO_ERROR_QUERY, errno, "Closing GPIO 'label'");
 
-    str[ret - 1] = '\0';
-
     return 0;
 }