[Tarantool-patches] [PATCH v5 1/2] base64: fix decoder output buffer overrun (reads)

[Sergey Nikiforov <void@tarantool.org>]

Was caught by base64 test with enabled ASAN.

It also caused data corruption - garbage instead of "extra bits" was
saved into state->result if there was no space in output buffer.

Added test for "zero-sized output buffer" case.

Fixes: #3069
---

Issue: https://github.com/tarantool/tarantool/issues/3069
Branch: https://github.com/tarantool/tarantool/tree/void234/gh-3069-fix-base64-memory-overrun-v5

 test/unit/base64.c      | 13 ++++++++++++-
 test/unit/base64.result |  3 ++-
 third_party/base64.c    | 28 +++++++++++++++++-----------
 3 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/test/unit/base64.c b/test/unit/base64.c
index ada497adf..c0ccf1321 100644
--- a/test/unit/base64.c
+++ b/test/unit/base64.c
@@ -58,9 +58,18 @@ base64_nowrap_test(const char *str)
 	base64_test(str, BASE64_NOWRAP, symbols, lengthof(symbols));
 }
 
+static void
+base64_no_space_test(void)
+{
+	const char *const in = "sIIpHw==";
+	const int in_len = strlen(in);
+	const int rc = base64_decode(in, in_len, NULL, 0);
+	is(rc, 0, "no space in out buffer");
+}
+
 int main(int argc, char *argv[])
 {
-	plan(28);
+	plan(29);
 	header();
 
 	const char *option_tests[] = {
@@ -78,6 +87,8 @@ int main(int argc, char *argv[])
 		base64_nowrap_test(option_tests[i]);
 	}
 
+	base64_no_space_test();
+
 	footer();
 	return check_plan();
 }
diff --git a/test/unit/base64.result b/test/unit/base64.result
index cd1f2b3f6..71b3519bf 100644
--- a/test/unit/base64.result
+++ b/test/unit/base64.result
@@ -1,4 +1,4 @@
-1..28
+1..29
 	*** main ***
     1..3
     ok 1 - length
@@ -175,4 +175,5 @@ ok 27 - subtests
     ok 3 - decode length ok
     ok 4 - encode/decode
 ok 28 - subtests
+ok 29 - no space in out buffer
 	*** main: done ***
diff --git a/third_party/base64.c b/third_party/base64.c
index 8ecab23eb..3350a98ff 100644
--- a/third_party/base64.c
+++ b/third_party/base64.c
@@ -247,8 +247,9 @@ 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)
 	{
@@ -259,49 +260,54 @@ base64_decode_block(const char *in_base64, int in_len,
 				if (in_pos == in_end || out_pos >= out_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)
 				{
 					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;
+			curr_byte |= (fragment & 0x030) >> 4;
+			*out_pos++ = curr_byte;
+			curr_byte = (fragment & 0x00f) << 4;
 			if (out_pos < out_end)
-				*out_pos = (fragment & 0x00f) << 4;
+				*out_pos = curr_byte;
 	case step_c:
 			do {
 				if (in_pos == in_end || out_pos >= out_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;
+			curr_byte |= (fragment & 0x03c) >> 2;
+			*out_pos++ = curr_byte;
+			curr_byte = (fragment & 0x003) << 6;
 			if (out_pos < out_end)
-				*out_pos = (fragment & 0x003) << 6;
+				*out_pos = curr_byte;
 	case step_d:
 			do {
 				if (in_pos == in_end || out_pos >= out_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;
 		}
 	}
 	/* control should not reach here */
-- 
2.25.1