From 1c2f37ede69caad5b247265566477f757a35dd21 Mon Sep 17 00:00:00 2001
From: cspark <git@cspark.dev>
Date: Sat, 20 Jul 2024 22:09:44 +0100
Subject: [PATCH] Fix buffer overflow and properly init pixel array

---
 .gitignore |   3 ++-
 lib/bmp.c  |  17 +++++++++++++----
 lib/bmp.h  |   1 +
 test.bmp   | Bin 70 -> 0 bytes
 4 files changed, 16 insertions(+), 5 deletions(-)
 delete mode 100755 test.bmp

diff --git a/.gitignore b/.gitignore
index f8305e7..fe2a10e 100755
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
-a.out
\ No newline at end of file
+a.out
+*.bmp
diff --git a/lib/bmp.c b/lib/bmp.c
index e04a703..da45a5f 100644
--- a/lib/bmp.c
+++ b/lib/bmp.c
@@ -5,16 +5,20 @@
 #include "bmp.h"
 
 uint32_t calc_bitmap_pixel_array_size_bytes(bitmap *bitmap_in) {
-	/* We will assume that the bitmap bits per pixel is always a multiple of 8 and sizeof byte is always 8 */
+	/* We will assume that the bitmap bits per pixel is always a multiple of 8 and sizeof byte is always 8 bits */
 	uint32_t bytes_unpadded = (bitmap_in->image_width * bitmap_in->image_height * bitmap_in->bits_per_pixel) / 8;
 	return bytes_unpadded + (bytes_unpadded % 8); /* Add padding to ensure 4 byte allignment */
 };
 
 uint32_t calc_bitmap_file_size_bytes(bitmap *bitmap_in) {
-	/* We will assume that the bitmap bits per pixel is always a multiple of 8 and sizeof byte is always 8 */
+	/* We will assume that the bitmap bits per pixel is always a multiple of 8 and sizeof byte is always 8 bits */
 	return sizeof(bitmap) + calc_bitmap_pixel_array_size_bytes(bitmap_in) - 2 ; /* Take away two to account for compiler padding struct */
 };
 
+uint32_t calc_bitmap_header_size_bytes() {
+	return sizeof(bitmap) - 2 ; /* Take away two to account for compiler padding struct */
+};
+
 bitmap init_bitmap(int32_t image_width_in, int32_t image_height_in) {
 	bitmap new_bitmap;
 	/* Bitmap Info Header */
@@ -44,12 +48,17 @@ bitmap init_bitmap(int32_t image_width_in, int32_t image_height_in) {
 
 int write_to_bitmap(bitmap *bitmap_in, char *filename) {
 	int8_t write_status;
+	uint32_t current_byte; 
+	uint8_t blank_byte_buffer[1] = { 0 }; 
 	uint8_t *bitmap_in_byte_ptr = (uint8_t *)bitmap_in + 2; /* Offset by two to account for padding */
 	int8_t fd = open(filename, O_WRONLY | O_CREAT);
 	if (fd == -1)
 		return -1;
-	/* This is writing out of bounds (bitmap < bitmap_file_size), please fix */
-	write_status = write(fd, bitmap_in_byte_ptr, calc_bitmap_file_size_bytes(bitmap_in));
+	/* Write Header */
+	write_status = write(fd, bitmap_in_byte_ptr, calc_bitmap_header_size_bytes());
+	/* Write blank pixel array */
+	for (current_byte = bitmap_in->image_data_start_offset; current_byte < calc_bitmap_file_size_bytes(bitmap_in); ++current_byte) 
+		write_status = pwrite(fd, blank_byte_buffer, 1, current_byte);
 	if (fd == -1) {
 		close(fd);
 		return -1;
diff --git a/lib/bmp.h b/lib/bmp.h
index e67eda4..1f8570b 100644
--- a/lib/bmp.h
+++ b/lib/bmp.h
@@ -44,6 +44,7 @@ bitmap init_bitmap(int32_t image_width_in, int32_t image_height_in);
 
 uint32_t calc_bitmap_file_size_bytes(bitmap *bitmap_in);
 uint32_t calc_bitmap_pixel_array_size_bytes(bitmap *bitmap_in);
+uint32_t calc_bitmap_header_size_bytes();
 
 int write_to_bitmap(bitmap *bitmap_in, char *filename);
 
diff --git a/test.bmp b/test.bmp
deleted file mode 100755
index 8243851c2107e2545f820924c409817f06151a47..0000000000000000000000000000000000000000
GIT binary patch
literal 0
HcmV?d00001

literal 70
lcmZ?rbz^`4Ga#h_#7t1k$RGih5CD?G+z<>FKq45SYye#`0iFN=