tools.c: refactored verify_ramdisk_digest()

This consists of several changes at once:
- purged unneccessary variables;
- fixed variable and function types;
- more readable return values;
- improved error logging;
- optimized hash printout just in case.

The original version of this patch fixed an off-by-one
issue too (it's been committed separately now).

cdrom.c

@@ -67,7 +67,9 @@ static int mount_that_cd_device(char * dev_name)
 /* test_that_cd() returns 0 on success */
 static int test_that_cd(int no_digest)
 {
-	if (IS_VERIFICATION && !no_digest) return !verify_ramdisk_digest(get_ramdisk_path(NULL), get_param_valued("hash"));
+	if (IS_VERIFICATION && !no_digest)
+		return verify_ramdisk_digest(get_ramdisk_path(NULL),
+				get_param_valued("hash")) == RETURN_ERROR;
 	log_message("test file on cd: %s\n", get_ramdisk_path(NULL));
 	return access(get_ramdisk_path(NULL), R_OK);
 }

tools.c

@@ -355,51 +355,60 @@ char * get_ramdisk_path(const char *mount_path)
 }
 
 /* This function is used to protect against stage2 (aka ramdisk) spoofing */
-int verify_ramdisk_digest(const char *filename, const char *sha256_hash)
+enum return_type verify_ramdisk_digest(const char *filename, const char *sha256_hash)
 {
-	FILE *fp;
-	char buffer[8192];
-	size_t len;
-	sha256_context ctx;
-	uint8 digest[32];
-	char computed_hash[64+1];
-	char * wait_msg = "Verifying stage2 authenticity...";
+	if (!sha256_hash)
+		return RETURN_ERROR;
+
+	int fd;
 	struct stat st;
-	int bytes_read = 0;
-	int ramdisk_size;
 
-	if(sha256_hash == NULL) return 0;
-
-	if(stat(filename, &st)) return 0;
-	ramdisk_size = st.st_size;
-
-	fp = fopen(filename, "rb");
-	if(fp == NULL) return 0;
-
-	init_progression(wait_msg, ramdisk_size);
-	sha256_starts(&ctx);
-	while((len = fread(buffer, 1, sizeof(buffer), fp)) > 0)
-	{
-		if(ferror(fp))
-		{
-			fclose(fp);
-			log_message("error reading ramdisk");
-			remove_wait_message();
-			return 0;
-		}
-		sha256_update(&ctx, buffer, len);
-		update_progression((int)(bytes_read += len));
+	if ((fd = open(filename, O_RDONLY)) < 0 || fstat(fd, &st)) {
+		log_message("verify_ramdisk_digest: %s: %m", filename);
+		close(fd);
+		return RETURN_ERROR;
 	}
-	sha256_finish(&ctx, digest);
+
+	init_progression("Verifying stage2 authenticity...", st.st_size);
+
+	sha256_context ctx;
+	sha256_starts(&ctx);
+
+	ssize_t bytes_read = 0, total_bytes_read = 0;
+	unsigned char buffer[8192];
+
+	while ((bytes_read = read(fd, buffer, sizeof(buffer)))) {
+		if (bytes_read < 0) {
+			if (EINTR == errno)
+				continue;
+			log_message("verify_ramdisk_digest: %s: %m", filename);
+			close(fd);
+			remove_wait_message();
+			return RETURN_ERROR;
+		}
+		sha256_update(&ctx, buffer, bytes_read);
+		total_bytes_read += bytes_read;
+		update_progression(total_bytes_read);
+	}
+
+	close(fd);
 	end_progression();
 
-	fclose(fp);
+	uint8 digest[256/8];
+	sha256_finish(&ctx, digest);
 
-	len = 0;
-	int i = 0;
-	for (i; i < 32; i++) len += sprintf(computed_hash + len, "%02x", digest[i]);
+	const char *hex = "0123456789abcdef";
+	unsigned i;
+	char computed_hash[sizeof(digest)*2 + 1];
+	char *dest = computed_hash;
 
-	return (strcmp(computed_hash, sha256_hash) == 0);
+	for (i = 0; i < sizeof(digest); ++i) {
+		*(dest++) = hex[(digest[i] >> 4) & 0xf];
+		*(dest++) = hex[digest[i] & 0xf];
+	}
+	*dest = '\0';
+
+	return strcmp(computed_hash, sha256_hash) ? RETURN_ERROR : RETURN_OK;
 }
 
 enum return_type load_ramdisk(char *mount_path)

tools.h

@@ -43,7 +43,7 @@ char ** list_directory(char * direct);
 int string_array_length(char ** a);
 int do_losetup(char * device, char * target);
 char * get_ramdisk_path(const char *);
-int verify_ramdisk_digest(const char *filename, const char *sha256_hash);
+enum return_type verify_ramdisk_digest(const char *filename, const char *sha256_hash);
 int splash_verbose();
 int update_splash(char * state);
 int prepare_progress(void);