Fix out of bound OLED font access (#8145)

* Fix out of bound OLED font access

The default font is 1344 bytes, or a total of 224 glyphs (each 6-bytes wide).
OLED_FONT_END defaults to 224, which if used will then index off the end of
the font array. So either the documentation or code is wrong.

Instead of figuring out the rewording of the documentation, just change
the OLED_FONT_END default value to 223, to match the documentation and code.

* Add static assert to check array size

Build bomb if the font array size doesn't match to the defines.

2 files changed, 5 insertions, 3 deletions

diff --git a/drivers/oled/oled_driver.c b/drivers/oled/oled_driver.c
index f20f4629a..e541228ea 100644
--- a/drivers/oled/oled_driver.c
+++ b/drivers/oled/oled_driver.c
@@ -392,6 +392,8 @@ void oled_write_char(const char data, bool invert) {
     static uint8_t oled_temp_buffer[OLED_FONT_WIDTH];
     memcpy(&oled_temp_buffer, oled_cursor, OLED_FONT_WIDTH);
 
+    _Static_assert(sizeof(font) >= ((OLED_FONT_END + 1 - OLED_FONT_START) * OLED_FONT_WIDTH), "OLED_FONT_END references outside array");
+
     // set the reder buffer data
     uint8_t cast_data = (uint8_t)data;  // font based on unsigned type for index
     if (cast_data < OLED_FONT_START || cast_data > OLED_FONT_END) {
@@ -585,4 +587,4 @@ void oled_task(void) {
 #endif
 }
 
-__attribute__((weak)) void oled_task_user(void) {}
\ No newline at end of file
+__attribute__((weak)) void oled_task_user(void) {}
diff --git a/drivers/oled/oled_driver.h b/drivers/oled/oled_driver.h
index f490f367a..e8a718857 100644
--- a/drivers/oled/oled_driver.h
+++ b/drivers/oled/oled_driver.h
@@ -131,7 +131,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #endif
 // unsigned char value of the last character in the font file
 #if !defined(OLED_FONT_END)
-#    define OLED_FONT_END 224
+#    define OLED_FONT_END 223
 #endif
 // Font render width
 #if !defined(OLED_FONT_WIDTH)
@@ -260,4 +260,4 @@ bool oled_scroll_off(void);
 uint8_t oled_max_chars(void);
 
 // Returns the maximum number of lines that will fit on the oled
-uint8_t oled_max_lines(void);
\ No newline at end of file
+uint8_t oled_max_lines(void);