Postpone allocation of STACK internal storage ... until a first push(),

insert() or an explicit call to OPENSSL_sk_reserve

Factorise STACK item deletion code
Reviewed-by: NAndy Polyakov <appro@openssl.org>
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4379)

crypto/stack/stack.c

@@ -55,6 +55,13 @@ OPENSSL_STACK *OPENSSL_sk_dup(const OPENSSL_STACK *sk)
     /* direct structure assignment */
     *ret = *sk;
 
+    if (sk->num == 0) {
+        /* postpone |ret->data| allocation */
+        ret->data = NULL;
+        ret->num_alloc = 0;
+        return ret;
+    }
+    /* duplicate |sk->data| content */
     if ((ret->data = OPENSSL_malloc(sizeof(*ret->data) * sk->num_alloc)) == NULL)
         goto err;
     memcpy(ret->data, sk->data, sizeof(void *) * sk->num);
@@ -80,6 +87,13 @@ OPENSSL_STACK *OPENSSL_sk_deep_copy(const OPENSSL_STACK *sk,
     /* direct structure assignment */
     *ret = *sk;
 
+    if (sk->num == 0) {
+        /* postpone |ret| data allocation */
+        ret->data = NULL;
+        ret->num_alloc = 0;
+        return ret;
+    }
+
     ret->num_alloc = sk->num > min_nodes ? sk->num : min_nodes;
     ret->data = OPENSSL_zalloc(sizeof(*ret->data) * ret->num_alloc);
     if (ret->data == NULL) {
@@ -103,41 +117,35 @@ OPENSSL_STACK *OPENSSL_sk_deep_copy(const OPENSSL_STACK *sk,
 
 OPENSSL_STACK *OPENSSL_sk_new_null(void)
 {
-    return OPENSSL_sk_new((OPENSSL_sk_compfunc)NULL);
+    return OPENSSL_zalloc(sizeof(OPENSSL_STACK));
 }
 
 OPENSSL_STACK *OPENSSL_sk_new(OPENSSL_sk_compfunc c)
 {
-    OPENSSL_STACK *ret;
+    OPENSSL_STACK *ret = OPENSSL_sk_new_null();
 
-    if ((ret = OPENSSL_zalloc(sizeof(*ret))) == NULL)
-        goto err;
-    if ((ret->data = OPENSSL_zalloc(sizeof(*ret->data) * min_nodes)) == NULL)
-        goto err;
+    if (ret != NULL)
         ret->comp = c;
-    ret->num_alloc = min_nodes;
-    return (ret);
-
- err:
-    OPENSSL_free(ret);
-    return (NULL);
+    return ret;
 }
 
 /*
  * Calculate the array growth based on the target size.
  *
- * The growth faction is a rational number and is defined by a numerator
+ * The growth fraction is a rational number and is defined by a numerator
  * and a denominator.  According to Andrew Koenig in his paper "Why Are
  * Vectors Efficient?" from JOOP 11(5) 1998, this factor should be less
  * than the golden ratio (1.618...).
  *
- * We use 3/2 = 1.5 for simplicty of calculation and overflow checking.
+ * We use 3/2 = 1.5 for simplicity of calculation and overflow checking.
  * Another option 8/5 = 1.6 allows for slightly faster growth, although safe
  * computation is more difficult.
  *
  * The limit to avoid overflow is spot on.  The modulo three correction term
  * ensures that the limit is the largest number than can be expanded by the
  * growth factor without exceeding the hard limit.
+ *
+ * Do not call it with |current| lower than 2, or it will infinitely loop.
  */
 static ossl_inline int compute_growth(int target, int current)
 {
@@ -154,6 +162,7 @@ static ossl_inline int compute_growth(int target, int current)
     return current;
 }
 
+/* internal STACK storage allocation */
 static int sk_reserve(OPENSSL_STACK *st, int n, int exact)
 {
     const void **tmpdata;
@@ -168,6 +177,19 @@ static int sk_reserve(OPENSSL_STACK *st, int n, int exact)
     if (num_alloc < min_nodes)
         num_alloc = min_nodes;
 
+    /* If |st->data| allocation was postponed */
+    if (st->data == NULL) {
+        /*
+         * At this point, |st->num_alloc| and |st->num| are 0;
+         * so |num_alloc| value is |n| or |min_nodes| if greater than |n|.
+         */
+        st->data = OPENSSL_zalloc(sizeof(void *) * num_alloc);
+        if (st->data == NULL)
+            return 0;
+        st->num_alloc = num_alloc;
+        return 1;
+    }
+
     if (!exact) {
         if (num_alloc <= st->num_alloc)
             return 1;
@@ -217,29 +239,34 @@ int OPENSSL_sk_insert(OPENSSL_STACK *st, const void *data, int loc)
     return st->num;
 }
 
+static ossl_inline void *internal_delete(OPENSSL_STACK *st, int loc)
+{
+    const void *ret = st->data[loc];
+
+    if (loc != st->num - 1)
+         memmove(&st->data[loc], &st->data[loc + 1],
+                 sizeof(st->data[0]) * (st->num - loc - 1));
+    st->num--;
+
+    return (void *)ret;
+}
+
 void *OPENSSL_sk_delete_ptr(OPENSSL_STACK *st, const void *p)
 {
     int i;
 
     for (i = 0; i < st->num; i++)
         if (st->data[i] == p)
-            return OPENSSL_sk_delete(st, i);
+            return internal_delete(st, i);
     return NULL;
 }
 
 void *OPENSSL_sk_delete(OPENSSL_STACK *st, int loc)
 {
-    const void *ret;
-
     if (st == NULL || loc < 0 || loc >= st->num)
         return NULL;
 
-    ret = st->data[loc];
-    if (loc != st->num - 1)
-         memmove(&st->data[loc], &st->data[loc + 1],
-                 sizeof(st->data[0]) * (st->num - loc - 1));
-    st->num--;
-    return (void *)ret;
+    return internal_delete(st, loc);
 }
 
 static int internal_find(OPENSSL_STACK *st, const void *data,
@@ -248,7 +275,7 @@ static int internal_find(OPENSSL_STACK *st, const void *data,
     const void *r;
     int i;
 
-    if (st == NULL)
+    if (st == NULL || st->num == 0)
         return -1;
 
     if (st->comp == NULL) {
@@ -279,7 +306,9 @@ int OPENSSL_sk_find_ex(OPENSSL_STACK *st, const void *data)
 
 int OPENSSL_sk_push(OPENSSL_STACK *st, const void *data)
 {
-    return (OPENSSL_sk_insert(st, data, st->num));
+    if (st == NULL)
+        return -1;
+    return OPENSSL_sk_insert(st, data, st->num);
 }
 
 int OPENSSL_sk_unshift(OPENSSL_STACK *st, const void *data)
@@ -290,19 +319,19 @@ int OPENSSL_sk_unshift(OPENSSL_STACK *st, const void *data)
 void *OPENSSL_sk_shift(OPENSSL_STACK *st)
 {
     if (st == NULL)
-        return (NULL);
+        return NULL;
     if (st->num <= 0)
-        return (NULL);
-    return (OPENSSL_sk_delete(st, 0));
+        return NULL;
+    return internal_delete(st, 0);
 }
 
 void *OPENSSL_sk_pop(OPENSSL_STACK *st)
 {
     if (st == NULL)
-        return (NULL);
+        return NULL;
     if (st->num <= 0)
-        return (NULL);
-    return (OPENSSL_sk_delete(st, st->num - 1));
+        return NULL;
+    return internal_delete(st, st->num - 1);
 }
 
 void OPENSSL_sk_zero(OPENSSL_STACK *st)
@@ -360,6 +389,7 @@ void *OPENSSL_sk_set(OPENSSL_STACK *st, int i, const void *data)
 void OPENSSL_sk_sort(OPENSSL_STACK *st)
 {
     if (st && !st->sorted && st->comp != NULL) {
+        if (st->data != NULL)
             qsort(st->data, st->num, sizeof(void *), st->comp);
         st->sorted = 1;
     }