[Tarantool-patches] [PATCH] Fix base64 decoder output buffer overrun (reads)

[Sergey Nikiforov <void@tarantool.org>]

It also caused data corruption.

Also:
Fixed read access beyond decode table (noticed along the way).
Minimized number of condition checks in internal loops (performance).

Fixes: #3069
---
 third_party/base64.c | 57 ++++++++++++++++++++++++++++++--------------
 1 file changed, 39 insertions(+), 18 deletions(-)

diff --git a/third_party/base64.c b/third_party/base64.c
index 8ecab23eb..ab644df22 100644
--- a/third_party/base64.c
+++ b/third_party/base64.c
@@ -222,7 +222,8 @@ base64_decode_value(int value)
 		32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43,
 		44, 45, 46, 47, 48, 49, 50, 51
 	};
-	static const int decoding_size = sizeof(decoding);
+	static const int decoding_size =
+		sizeof(decoding) / sizeof(decoding[0]);
 	int codepos = value;
 	codepos -= 43;
 	if (codepos < 0 || codepos >= decoding_size)
@@ -247,8 +248,9 @@ base64_decode_block(const char *in_base64, int in_len,
 	char *out_pos = out_bin;
 	char *out_end = out_bin + out_len;
 	int fragment;
+	char curr_byte;
 
-	*out_pos = state->result;
+	curr_byte = state->result;
 
 	switch (state->step)
 	{
@@ -256,52 +258,71 @@ base64_decode_block(const char *in_base64, int in_len,
 		{
 	case step_a:
 			do {
-				if (in_pos == in_end || out_pos >= out_end)
+				if (in_pos >= in_end)
 				{
 					state->step = step_a;
-					state->result = *out_pos;
+					state->result = curr_byte;
 					return out_pos - out_bin;
 				}
 				fragment = base64_decode_value(*in_pos++);
 			} while (fragment < 0);
-			*out_pos    = (fragment & 0x03f) << 2;
+			curr_byte = (fragment & 0x03f) << 2;
 	case step_b:
 			do {
-				if (in_pos == in_end || out_pos >= out_end)
+				if (in_pos >= in_end)
 				{
 					state->step = step_b;
-					state->result = *out_pos;
+					state->result = curr_byte;
 					return out_pos - out_bin;
 				}
 				fragment = base64_decode_value(*in_pos++);
 			} while (fragment < 0);
-			*out_pos++ |= (fragment & 0x030) >> 4;
-			if (out_pos < out_end)
-				*out_pos = (fragment & 0x00f) << 4;
+			curr_byte |= (fragment & 0x030) >> 4;
+			*out_pos = curr_byte;
+			curr_byte = (fragment & 0x00f) << 4;
+			if (++out_pos >= out_end)
+			{
+				state->step = step_c;
+				state->result = curr_byte;
+				return out_pos - out_bin;
+			}
 	case step_c:
 			do {
-				if (in_pos == in_end || out_pos >= out_end)
+				if (in_pos >= in_end)
 				{
 					state->step = step_c;
-					state->result = *out_pos;
+					state->result = curr_byte;
 					return out_pos - out_bin;
 				}
 				fragment = base64_decode_value(*in_pos++);
 			} while (fragment < 0);
-			*out_pos++ |= (fragment & 0x03c) >> 2;
-			if (out_pos < out_end)
-				*out_pos = (fragment & 0x003) << 6;
+			curr_byte |= (fragment & 0x03c) >> 2;
+			*out_pos = curr_byte;
+			curr_byte = (fragment & 0x003) << 6;
+			if (++out_pos >= out_end)
+			{
+				state->step = step_d;
+				state->result = curr_byte;
+				return out_pos - out_bin;
+			}
 	case step_d:
 			do {
-				if (in_pos == in_end || out_pos >= out_end)
+				if (in_pos >= in_end)
 				{
 					state->step = step_d;
-					state->result = *out_pos;
+					state->result = curr_byte;
 					return out_pos - out_bin;
 				}
 				fragment = base64_decode_value(*in_pos++);
 			} while (fragment < 0);
-			*out_pos++   |= (fragment & 0x03f);
+			curr_byte |= (fragment & 0x03f);
+			*out_pos = curr_byte;
+			if (++out_pos >= out_end)
+			{
+				state->step = step_a;
+				state->result = curr_byte;
+				return out_pos - out_bin;
+			}
 		}
 	}
 	/* control should not reach here */
-- 
2.25.1