bpf: hashtab: move attribute validation before allocation

Number of attribute checks are currently performed after hashtab
is already allocated.  Move them to be able to split them out to
the check function later on.  Checks have to now be performed on
the attr union directly instead of the members of bpf_map, since
bpf_map will be allocated later.  No functional changes.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

kernel/bpf/hashtab.c

@@ -269,6 +269,28 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 	if (numa_node != NUMA_NO_NODE && (percpu || percpu_lru))
 		return ERR_PTR(-EINVAL);
 
+	/* check sanity of attributes.
+	 * value_size == 0 may be allowed in the future to use map as a set
+	 */
+	if (attr->max_entries == 0 || attr->key_size == 0 ||
+	    attr->value_size == 0)
+		return ERR_PTR(-EINVAL);
+
+	if (attr->key_size > MAX_BPF_STACK)
+		/* eBPF programs initialize keys on stack, so they cannot be
+		 * larger than max stack size
+		 */
+		return ERR_PTR(-E2BIG);
+
+	if (attr->value_size >= KMALLOC_MAX_SIZE -
+	    MAX_BPF_STACK - sizeof(struct htab_elem))
+		/* if value_size is bigger, the user space won't be able to
+		 * access the elements via bpf syscall. This check also makes
+		 * sure that the elem_size doesn't overflow and it's
+		 * kmalloc-able later in htab_map_update_elem()
+		 */
+		return ERR_PTR(-E2BIG);
+
 	htab = kzalloc(sizeof(*htab), GFP_USER);
 	if (!htab)
 		return ERR_PTR(-ENOMEM);
@@ -281,14 +303,6 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 	htab->map.map_flags = attr->map_flags;
 	htab->map.numa_node = numa_node;
 
-	/* check sanity of attributes.
-	 * value_size == 0 may be allowed in the future to use map as a set
-	 */
-	err = -EINVAL;
-	if (htab->map.max_entries == 0 || htab->map.key_size == 0 ||
-	    htab->map.value_size == 0)
-		goto free_htab;
-
 	if (percpu_lru) {
 		/* ensure each CPU's lru list has >=1 elements.
 		 * since we are at it, make each lru list has the same
@@ -304,22 +318,6 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 	/* hash table size must be power of 2 */
 	htab->n_buckets = roundup_pow_of_two(htab->map.max_entries);
 
-	err = -E2BIG;
-	if (htab->map.key_size > MAX_BPF_STACK)
-		/* eBPF programs initialize keys on stack, so they cannot be
-		 * larger than max stack size
-		 */
-		goto free_htab;
-
-	if (htab->map.value_size >= KMALLOC_MAX_SIZE -
-	    MAX_BPF_STACK - sizeof(struct htab_elem))
-		/* if value_size is bigger, the user space won't be able to
-		 * access the elements via bpf syscall. This check also makes
-		 * sure that the elem_size doesn't overflow and it's
-		 * kmalloc-able later in htab_map_update_elem()
-		 */
-		goto free_htab;
-
 	htab->elem_size = sizeof(struct htab_elem) +
 			  round_up(htab->map.key_size, 8);
 	if (percpu)
@@ -327,6 +325,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 	else
 		htab->elem_size += round_up(htab->map.value_size, 8);
 
+	err = -E2BIG;
 	/* prevent zero size kmalloc and check for u32 overflow */
 	if (htab->n_buckets == 0 ||
 	    htab->n_buckets > U32_MAX / sizeof(struct bucket))