apply: fix leaking string in match_fragment()

Before calling `update_pre_post_images()`, we call `strbuf_detach()` to
put its buffer into a new string variable that we then pass to that
function. Besides being rather pointless, it also causes us to leak
memory of that variable because we never free it.

Get rid of the variable altogether and instead reach into the `strbuf`
directly. While at it, refactor the code to have a common exit path and
mark string that do not contain allocated memory as constant.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

apply.c

@@ -2494,18 +2494,21 @@ static int match_fragment(struct apply_state *state,
 			  int match_beginning, int match_end)
 {
 	int i;
-	char *fixed_buf, *buf, *orig, *target;
-	struct strbuf fixed;
-	size_t fixed_len, postlen;
+	const char *orig, *target;
+	struct strbuf fixed = STRBUF_INIT;
+	size_t postlen;
 	int preimage_limit;
+	int ret;
 
 	if (preimage->nr + current_lno <= img->nr) {
 		/*
 		 * The hunk falls within the boundaries of img.
 		 */
 		preimage_limit = preimage->nr;
-		if (match_end && (preimage->nr + current_lno != img->nr))
-			return 0;
+		if (match_end && (preimage->nr + current_lno != img->nr)) {
+			ret = 0;
+			goto out;
+		}
 	} else if (state->ws_error_action == correct_ws_error &&
 		   (ws_rule & WS_BLANK_AT_EOF)) {
 		/*
@@ -2522,17 +2525,23 @@ static int match_fragment(struct apply_state *state,
 		 * we are not removing blanks at the end, so we
 		 * should reject the hunk at this position.
 		 */
-		return 0;
+		ret = 0;
+		goto out;
 	}
 
-	if (match_beginning && current_lno)
-		return 0;
+	if (match_beginning && current_lno) {
+		ret = 0;
+		goto out;
+	}
 
 	/* Quick hash check */
-	for (i = 0; i < preimage_limit; i++)
+	for (i = 0; i < preimage_limit; i++) {
 		if ((img->line[current_lno + i].flag & LINE_PATCHED) ||
-		    (preimage->line[i].hash != img->line[current_lno + i].hash))
-			return 0;
+		    (preimage->line[i].hash != img->line[current_lno + i].hash)) {
+			ret = 0;
+			goto out;
+		}
+	}
 
 	if (preimage_limit == preimage->nr) {
 		/*
@@ -2545,8 +2554,10 @@ static int match_fragment(struct apply_state *state,
 		if ((match_end
 		     ? (current + preimage->len == img->len)
 		     : (current + preimage->len <= img->len)) &&
-		    !memcmp(img->buf + current, preimage->buf, preimage->len))
-			return 1;
+		    !memcmp(img->buf + current, preimage->buf, preimage->len)) {
+			ret = 1;
+			goto out;
+		}
 	} else {
 		/*
 		 * The preimage extends beyond the end of img, so
@@ -2555,7 +2566,7 @@ static int match_fragment(struct apply_state *state,
 		 * There must be one non-blank context line that match
 		 * a line before the end of img.
 		 */
-		char *buf_end;
+		const char *buf, *buf_end;
 
 		buf = preimage->buf;
 		buf_end = buf;
@@ -2565,21 +2576,27 @@ static int match_fragment(struct apply_state *state,
 		for ( ; buf < buf_end; buf++)
 			if (!isspace(*buf))
 				break;
-		if (buf == buf_end)
-			return 0;
+		if (buf == buf_end) {
+			ret = 0;
+			goto out;
+		}
 	}
 
 	/*
 	 * No exact match. If we are ignoring whitespace, run a line-by-line
 	 * fuzzy matching. We collect all the line length information because
 	 * we need it to adjust whitespace if we match.
 	 */
-	if (state->ws_ignore_action == ignore_ws_change)
-		return line_by_line_fuzzy_match(img, preimage, postimage,
-						current, current_lno, preimage_limit);
+	if (state->ws_ignore_action == ignore_ws_change) {
+		ret = line_by_line_fuzzy_match(img, preimage, postimage,
+					       current, current_lno, preimage_limit);
+		goto out;
+	}
 
-	if (state->ws_error_action != correct_ws_error)
-		return 0;
+	if (state->ws_error_action != correct_ws_error) {
+		ret = 0;
+		goto out;
+	}
 
 	/*
 	 * The hunk does not apply byte-by-byte, but the hash says
@@ -2608,7 +2625,7 @@ static int match_fragment(struct apply_state *state,
 	 * but in this loop we will only handle the part of the
 	 * preimage that falls within the file.
 	 */
-	strbuf_init(&fixed, preimage->len + 1);
+	strbuf_grow(&fixed, preimage->len + 1);
 	orig = preimage->buf;
 	target = img->buf + current;
 	for (i = 0; i < preimage_limit; i++) {
@@ -2644,8 +2661,10 @@ static int match_fragment(struct apply_state *state,
 			postlen += tgtfix.len;
 
 		strbuf_release(&tgtfix);
-		if (!match)
-			goto unmatch_exit;
+		if (!match) {
+			ret = 0;
+			goto out;
+		}
 
 		orig += oldlen;
 		target += tgtlen;
@@ -2666,9 +2685,13 @@ static int match_fragment(struct apply_state *state,
 		/* Try fixing the line in the preimage */
 		ws_fix_copy(&fixed, orig, oldlen, ws_rule, NULL);
 
-		for (j = fixstart; j < fixed.len; j++)
-			if (!isspace(fixed.buf[j]))
-				goto unmatch_exit;
+		for (j = fixstart; j < fixed.len; j++) {
+			if (!isspace(fixed.buf[j])) {
+				ret = 0;
+				goto out;
+			}
+		}
+
 
 		orig += oldlen;
 	}
@@ -2678,16 +2701,16 @@ static int match_fragment(struct apply_state *state,
 	 * has whitespace breakages unfixed, and fixing them makes the
 	 * hunk match.  Update the context lines in the postimage.
 	 */
-	fixed_buf = strbuf_detach(&fixed, &fixed_len);
 	if (postlen < postimage->len)
 		postlen = 0;
 	update_pre_post_images(preimage, postimage,
-			       fixed_buf, fixed_len, postlen);
-	return 1;
+			       fixed.buf, fixed.len, postlen);
 
- unmatch_exit:
+	ret = 1;
+
+out:
 	strbuf_release(&fixed);
-	return 0;
+	return ret;
 }
 
 static int find_pos(struct apply_state *state,

t/t3417-rebase-whitespace-fix.sh

@@ -5,6 +5,7 @@ test_description='git rebase --whitespace=fix
 This test runs git rebase --whitespace=fix and make sure that it works.
 '
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 # prepare initial revision of "file" with a blank line at the end