[Tarantool-patches] [PATCH v6 1/2] base64: fix decoder output buffer overrun (reads)

[Sergey Nikiforov]

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
---

Branch: https://github.com/tarantool/tarantool/tree/void234/gh-3069-fix-base64-memory-overrun-v6
Issue: https://github.com/tarantool/tarantool/issues/3069

 test/unit/base64.c      | 16 +++++++++++++++-
 test/unit/base64.result |  5 ++++-
 third_party/base64.c    | 28 +++++++++++++++++-----------
 3 files changed, 36 insertions(+), 13 deletions(-)

diff --git a/test/unit/base64.c b/test/unit/base64.c
index cc74f64d1..508877217 100644
--- a/test/unit/base64.c
+++ b/test/unit/base64.c
@@ -75,9 +75,22 @@ base64_invalid_chars_test(void)
 	check_plan();
 }
 
+static void
+base64_no_space_test(void)
+{
+	plan(1);
+
+	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");
+
+	check_plan();
+}
+
 int main(int argc, char *argv[])
 {
-	plan(29);
+	plan(30);
 	header();
 
 	const char *option_tests[] = {
@@ -96,6 +109,7 @@ int main(int argc, char *argv[])
 	}
 
 	base64_invalid_chars_test();
+	base64_no_space_test();
 
 	footer();
 	return check_plan();
diff --git a/test/unit/base64.result b/test/unit/base64.result
index 3bc2c2275..495e2d0a2 100644
--- a/test/unit/base64.result
+++ b/test/unit/base64.result
@@ -1,4 +1,4 @@
-1..29
+1..30
 	*** main ***
     1..3
     ok 1 - length
@@ -178,4 +178,7 @@ ok 28 - subtests
     1..1
     ok 1 - ignoring invalid chars
 ok 29 - subtests
+    1..1
+    ok 1 - no space in out buffer
+ok 30 - subtests
 	*** main: done ***
diff --git a/third_party/base64.c b/third_party/base64.c
index 7c69315ea..3ecd0843a 100644
--- a/third_party/base64.c
+++ b/third_party/base64.c
@@ -248,8 +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)
 	{
@@ -260,49 +261,54 @@ 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