xdiff: fix a memory leak

Although the patience and histogram algorithms initialize the
environment they do not free it if there is an error. In contrast for
the Myers algorithm the environment is initalized in xdl_do_diff() and
it is freed if there is an error. Fix this by always initializing the
environment in xdl_do_diff() and freeing it there if there is an
error. Remove the comment in do_patience_diff() about the environment
being freed by xdl_diff() as it is not accurate because (a) xdl_diff()
does not do that if there is an error and (b) xdl_diff() is not the
only caller.

Reported-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 17 insertions, 16 deletions

diff --git a/xdiff/xdiffi.c b/xdiff/xdiffi.c
index 69689fab24..758410c11a 100644
--- a/xdiff/xdiffi.c
+++ b/xdiff/xdiffi.c
@@ -315,16 +315,19 @@ int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	long *kvd, *kvdf, *kvdb;
 	xdalgoenv_t xenv;
 	diffdata_t dd1, dd2;
+	int res;
 
-	if (XDF_DIFF_ALG(xpp->flags) == XDF_PATIENCE_DIFF)
-		return xdl_do_patience_diff(mf1, mf2, xpp, xe);
-
-	if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF)
-		return xdl_do_histogram_diff(mf1, mf2, xpp, xe);
+	if (xdl_prepare_env(mf1, mf2, xpp, xe) < 0)
+		return -1;
 
-	if (xdl_prepare_env(mf1, mf2, xpp, xe) < 0) {
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_PATIENCE_DIFF) {
+		res = xdl_do_patience_diff(mf1, mf2, xpp, xe);
+		goto out;
+	}
 
-		return -1;
+	if (XDF_DIFF_ALG(xpp->flags) == XDF_HISTOGRAM_DIFF) {
+		res = xdl_do_histogram_diff(mf1, mf2, xpp, xe);
+		goto out;
 	}
 
 	/*
@@ -359,17 +362,15 @@ int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	dd2.rchg = xe->xdf2.rchg;
 	dd2.rindex = xe->xdf2.rindex;
 
-	if (xdl_recs_cmp(&dd1, 0, dd1.nrec, &dd2, 0, dd2.nrec,
-			 kvdf, kvdb, (xpp->flags & XDF_NEED_MINIMAL) != 0, &xenv) < 0) {
-
-		xdl_free(kvd);
-		xdl_free_env(xe);
-		return -1;
-	}
-
+	res = xdl_recs_cmp(&dd1, 0, dd1.nrec, &dd2, 0, dd2.nrec,
+			   kvdf, kvdb, (xpp->flags & XDF_NEED_MINIMAL) != 0,
+			   &xenv);
 	xdl_free(kvd);
+ out:
+	if (res < 0)
+		xdl_free_env(xe);
 
-	return 0;
+	return res;
 }