From fb4f429493d6e942652951c94ace2c3d57ccc726 Mon Sep 17 00:00:00 2001
From: LoRd_MuldeR <mulder2@gmx.de>
Date: Tue, 1 Dec 2020 03:03:49 +0100
Subject: [PATCH] Ignore excess bytes, if length of input file is *not* an
 integer multiple of 8.

---
 frontend/src/main.c  |  6 +++++-
 frontend/src/utils.c | 10 ++++++++++
 frontend/src/utils.h |  1 +
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/frontend/src/main.c b/frontend/src/main.c
index 420768d..339352f 100644
--- a/frontend/src/main.c
+++ b/frontend/src/main.c
@@ -358,6 +358,10 @@ static int decrypt(const char* const passphrase, const CHR* const input_path, co
 		FPUTS(T("Error: Input file is too small! Truncated?\n\n"), stderr);
 		goto clean_up;
 	}
+	else if ((file_size % sizeof(uint64_t)) != 0)
+	{
+		FPRINTF(stderr, T("Warning: File size is *not* an integer multiple of %u, ignoring excess bytes!\n\n"), sizeof(uint64_t));
+	}
 
 	FPUTS(T("Decrypting file contents, please be patient... "), stderr);
 	fflush(stderr);
@@ -379,7 +383,7 @@ static int decrypt(const char* const passphrase, const CHR* const input_path, co
 	clock_t clk_now, clk_update = clock();
 	uint64_t crc_actual = CRC_INITIALIZER, bytes_read = sizeof(uint64_t);
 	uint8_t buffer[BUFFER_SIZE];
-	const uint64_t read_limit = file_size - (2U * sizeof(uint64_t));
+	const uint64_t read_limit = round_down(file_size, sizeof(uint64_t)) - (2U * sizeof(uint64_t));
 
 	FPRINTF(stderr, T("%5.1f%% "), 0.0);
 	fflush(stderr);
diff --git a/frontend/src/utils.c b/frontend/src/utils.c
index 016db2d..c2494c1 100644
--- a/frontend/src/utils.c
+++ b/frontend/src/utils.c
@@ -177,3 +177,13 @@ const CHR* get_file_name(const CHR* path)
 	}
 	return path;
 }
+
+// ==========================================================================
+// Math functions
+// ==========================================================================
+
+uint64_t round_down(const uint64_t value, const uint64_t base)
+{
+	const uint64_t modulus = value % base;
+	return modulus ? (value - modulus) : value;
+}
diff --git a/frontend/src/utils.h b/frontend/src/utils.h
index 01e60a1..b4556a3 100644
--- a/frontend/src/utils.h
+++ b/frontend/src/utils.h
@@ -17,6 +17,7 @@ uint64_t swap_bytes_u64(const uint64_t value);
 char* CHR_to_utf8(const CHR *const input);
 uint64_t get_file_size(FILE* const file);
 const CHR *get_file_name(const CHR *path);
+uint64_t round_down(const uint64_t value, const uint64_t base);
 
 #define GET_NIBBLE(X) ((X) & 0x0F)
 #define SET_NIBBLE(X, Y) do { X = ((X) & 0xF0) | ((Y) & 0x0F); } while(0)