From 9df0fc3d578acfdeb7fa1914fcf0507adb021fa5 Mon Sep 17 00:00:00 2001
From: Phillip Wood <phillip.wood@dunelm.org.uk>
Date: Wed, 16 Feb 2022 10:15:06 +0000
Subject: 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>

diff --git a/xdiff/xdiffi.c b/xdiff/xdiffi.c
index 69689fa..758410c 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;
 }
 
 
diff --git a/xdiff/xhistogram.c b/xdiff/xhistogram.c
index 8079474..01decff 100644
--- a/xdiff/xhistogram.c
+++ b/xdiff/xhistogram.c
@@ -372,9 +372,6 @@ out:
 int xdl_do_histogram_diff(mmfile_t *file1, mmfile_t *file2,
 	xpparam_t const *xpp, xdfenv_t *env)
 {
-	if (xdl_prepare_env(file1, file2, xpp, env) < 0)
-		return -1;
-
 	return histogram_diff(xpp, env,
 		env->xdf1.dstart + 1, env->xdf1.dend - env->xdf1.dstart + 1,
 		env->xdf2.dstart + 1, env->xdf2.dend - env->xdf2.dstart + 1);
diff --git a/xdiff/xpatience.c b/xdiff/xpatience.c
index c5d48e8..e8de8d1 100644
--- a/xdiff/xpatience.c
+++ b/xdiff/xpatience.c
@@ -373,10 +373,6 @@ static int patience_diff(mmfile_t *file1, mmfile_t *file2,
 int xdl_do_patience_diff(mmfile_t *file1, mmfile_t *file2,
 		xpparam_t const *xpp, xdfenv_t *env)
 {
-	if (xdl_prepare_env(file1, file2, xpp, env) < 0)
-		return -1;
-
-	/* environment is cleaned up in xdl_diff() */
 	return patience_diff(file1, file2, xpp, env,
 			1, env->xdf1.nrec, 1, env->xdf2.nrec);
 }
-- 
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