[PATCH 1/3] xdiff: introduce XDL_ALLOC_ARRAY()

["Phillip Wood via GitGitGadget" <gitgitgadget@gmail.com>]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

Add a helper to allocate an array that automatically calculates the
allocation size. This is analogous to ALLOC_ARRAY() in the rest of the
codebase but returns NULL if the allocation fails to accommodate other
users of libxdiff such as libgit2. The helper will also return NULL if
the multiplication in the allocation calculation overflows.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 xdiff/xdiffi.c    | 2 +-
 xdiff/xmacros.h   | 5 +++++
 xdiff/xpatience.c | 4 ++--
 xdiff/xprepare.c  | 8 ++++----
 4 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/xdiff/xdiffi.c b/xdiff/xdiffi.c
index 758410c11ac..53e803e6bcb 100644
--- a/xdiff/xdiffi.c
+++ b/xdiff/xdiffi.c
@@ -337,7 +337,7 @@ int xdl_do_diff(mmfile_t *mf1, mmfile_t *mf2, xpparam_t const *xpp,
 	 * One is to store the forward path and one to store the backward path.
 	 */
 	ndiags = xe->xdf1.nreff + xe->xdf2.nreff + 3;
-	if (!(kvd = (long *) xdl_malloc((2 * ndiags + 2) * sizeof(long)))) {
+	if (!XDL_ALLOC_ARRAY(kvd, 2 * ndiags + 2)) {
 
 		xdl_free_env(xe);
 		return -1;
diff --git a/xdiff/xmacros.h b/xdiff/xmacros.h
index ae4636c2477..9fd3c5da91a 100644
--- a/xdiff/xmacros.h
+++ b/xdiff/xmacros.h
@@ -49,5 +49,10 @@ do { \
 		((unsigned long) __p[2]) << 16 | ((unsigned long) __p[3]) << 24; \
 } while (0)
 
+/* Allocate an array of nr elements, returns NULL on failure */
+#define XDL_ALLOC_ARRAY(p, nr)				\
+	((p) = SIZE_MAX / sizeof(*(p)) >= (size_t)(nr)	\
+		? xdl_malloc((nr) * sizeof(*(p)))	\
+		: NULL)
 
 #endif /* #if !defined(XMACROS_H) */
diff --git a/xdiff/xpatience.c b/xdiff/xpatience.c
index 1a21c6a74b3..ce87b9084ca 100644
--- a/xdiff/xpatience.c
+++ b/xdiff/xpatience.c
@@ -200,7 +200,7 @@ static int binary_search(struct entry **sequence, int longest,
  */
 static int find_longest_common_sequence(struct hashmap *map, struct entry **res)
 {
-	struct entry **sequence = xdl_malloc(map->nr * sizeof(struct entry *));
+	struct entry **sequence;
 	int longest = 0, i;
 	struct entry *entry;
 
@@ -211,7 +211,7 @@ static int find_longest_common_sequence(struct hashmap *map, struct entry **res)
 	 */
 	int anchor_i = -1;
 
-	if (!sequence)
+	if (!XDL_ALLOC_ARRAY(sequence, map->nr))
 		return -1;
 
 	for (entry = map->first; entry; entry = entry->next) {
diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
index 105752758f2..25866a1667a 100644
--- a/xdiff/xprepare.c
+++ b/xdiff/xprepare.c
@@ -86,7 +86,7 @@ static int xdl_init_classifier(xdlclassifier_t *cf, long size, long flags) {
 	memset(cf->rchash, 0, cf->hsize * sizeof(xdlclass_t *));
 
 	cf->alloc = size;
-	if (!(cf->rcrecs = (xdlclass_t **) xdl_malloc(cf->alloc * sizeof(xdlclass_t *)))) {
+	if (!XDL_ALLOC_ARRAY(cf->rcrecs, cf->alloc)) {
 
 		xdl_free(cf->rchash);
 		xdl_cha_free(&cf->ncha);
@@ -178,7 +178,7 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
 
 	if (xdl_cha_init(&xdf->rcha, sizeof(xrecord_t), narec / 4 + 1) < 0)
 		goto abort;
-	if (!(recs = (xrecord_t **) xdl_malloc(narec * sizeof(xrecord_t *))))
+	if (!XDL_ALLOC_ARRAY(recs, narec))
 		goto abort;
 
 	hbits = xdl_hashbits((unsigned int) narec);
@@ -215,9 +215,9 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
 
 	if ((XDF_DIFF_ALG(xpp->flags) != XDF_PATIENCE_DIFF) &&
 	    (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF)) {
-		if (!(rindex = xdl_malloc((nrec + 1) * sizeof(*rindex))))
+		if (!XDL_ALLOC_ARRAY(rindex, nrec + 1))
 			goto abort;
-		if (!(ha = xdl_malloc((nrec + 1) * sizeof(*ha))))
+		if (!XDL_ALLOC_ARRAY(ha, nrec + 1))
 			goto abort;
 	}
 
-- 
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