Re: [PATCH 5/6] selinux: convert cond_expr to array

[Stephen Smalley <sds@xxxxxxxxxxxxx>]

On 1/16/20 7:04 AM, Ondrej Mosnacek wrote:
> Since it is fixed-size after allocation and we know the size beforehand,
> using a plain old array is simpler and more efficient.
>
> Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>

Reviewed-by: Stephen Smalley <sds@xxxxxxxxxxxxx>

> ---
>   security/selinux/ss/conditional.c | 62 ++++++++++++-------------------
>   security/selinux/ss/conditional.h | 14 ++++---
>   2 files changed, 33 insertions(+), 43 deletions(-)
>
> diff --git a/security/selinux/ss/conditional.c b/security/selinux/ss/conditional.c
> index b847fd2a6a51..8f9f2f3c86a0 100644
> --- a/security/selinux/ss/conditional.c
> +++ b/security/selinux/ss/conditional.c
> @@ -23,18 +23,19 @@
>    */
>   static int cond_evaluate_expr(struct policydb *p, struct cond_expr *expr)
>   {
> -
> -	struct cond_expr *cur;
> +	u32 i;
>   	int s[COND_EXPR_MAXDEPTH];
>   	int sp = -1;
>   
> -	for (cur = expr; cur; cur = cur->next) {
> -		switch (cur->expr_type) {
> +	for (i = 0; i < expr->len; i++) {
> +		struct cond_expr_node *node = &expr->nodes[i];
> +
> +		switch (node->expr_type) {
>   		case COND_BOOL:
>   			if (sp == (COND_EXPR_MAXDEPTH - 1))
>   				return -1;
>   			sp++;
> -			s[sp] = p->bool_val_to_struct[cur->bool - 1]->state;
> +			s[sp] = p->bool_val_to_struct[node->bool - 1]->state;
>   			break;
>   		case COND_NOT:
>   			if (sp < 0)
> @@ -91,7 +92,7 @@ void evaluate_cond_node(struct policydb *p, struct cond_node *node)
>   	int new_state;
>   	u32 i;
>   
> -	new_state = cond_evaluate_expr(p, node->expr);
> +	new_state = cond_evaluate_expr(p, &node->expr);
>   	if (new_state != node->cur_state) {
>   		node->cur_state = new_state;
>   		if (new_state == -1)
> @@ -133,12 +134,7 @@ int cond_policydb_init(struct policydb *p)
>   
>   static void cond_node_destroy(struct cond_node *node)
>   {
> -	struct cond_expr *cur_expr, *next_expr;
> -
> -	for (cur_expr = node->expr; cur_expr; cur_expr = next_expr) {
> -		next_expr = cur_expr->next;
> -		kfree(cur_expr);
> -	}
> +	kfree(node->expr.nodes);
>   	/* the avtab_ptr_t nodes are destroyed by the avtab */
>   	kfree(node->true_list.nodes);
>   	kfree(node->false_list.nodes);
> @@ -354,7 +350,7 @@ static int cond_read_av_list(struct policydb *p, void *fp,
>   	return 0;
>   }
>   
> -static int expr_isvalid(struct policydb *p, struct cond_expr *expr)
> +static int expr_node_isvalid(struct policydb *p, struct cond_expr_node *expr)
>   {
>   	if (expr->expr_type <= 0 || expr->expr_type > COND_LAST) {
>   		pr_err("SELinux: conditional expressions uses unknown operator.\n");
> @@ -371,43 +367,37 @@ static int expr_isvalid(struct policydb *p, struct cond_expr *expr)
>   static int cond_read_node(struct policydb *p, struct cond_node *node, void *fp)
>   {
>   	__le32 buf[2];
> -	u32 len, i;
> +	u32 i, len;
>   	int rc;
> -	struct cond_expr *expr = NULL, *last = NULL;
>   
>   	rc = next_entry(buf, fp, sizeof(u32) * 2);
>   	if (rc)
> -		goto err;
> +		return rc;
>   
>   	node->cur_state = le32_to_cpu(buf[0]);
>   
>   	/* expr */
>   	len = le32_to_cpu(buf[1]);
> +	node->expr.nodes = kcalloc(len, sizeof(*node->expr.nodes), GFP_KERNEL);
> +	if (!node->expr.nodes)
> +		return -ENOMEM;
> +
> +	node->expr.len = len;
>   
>   	for (i = 0; i < len; i++) {
> +		struct cond_expr_node *expr = &node->expr.nodes[i];
> +
>   		rc = next_entry(buf, fp, sizeof(u32) * 2);
>   		if (rc)
>   			goto err;
>   
> -		rc = -ENOMEM;
> -		expr = kzalloc(sizeof(*expr), GFP_KERNEL);
> -		if (!expr)
> -			goto err;
> -
>   		expr->expr_type = le32_to_cpu(buf[0]);
>   		expr->bool = le32_to_cpu(buf[1]);
>   
> -		if (!expr_isvalid(p, expr)) {
> +		if (!expr_node_isvalid(p, expr)) {
>   			rc = -EINVAL;
> -			kfree(expr);
>   			goto err;
>   		}
> -
> -		if (i == 0)
> -			node->expr = expr;
> -		else
> -			last->next = expr;
> -		last = expr;
>   	}
>   
>   	rc = cond_read_av_list(p, fp, &node->true_list, NULL);
> @@ -512,27 +502,23 @@ static int cond_write_av_list(struct policydb *p,
>   static int cond_write_node(struct policydb *p, struct cond_node *node,
>   		    struct policy_file *fp)
>   {
> -	struct cond_expr *cur_expr;
>   	__le32 buf[2];
>   	int rc;
> -	u32 len = 0;
> +	u32 i;
>   
>   	buf[0] = cpu_to_le32(node->cur_state);
>   	rc = put_entry(buf, sizeof(u32), 1, fp);
>   	if (rc)
>   		return rc;
>   
> -	for (cur_expr = node->expr; cur_expr != NULL; cur_expr = cur_expr->next)
> -		len++;
> -
> -	buf[0] = cpu_to_le32(len);
> +	buf[0] = cpu_to_le32(node->expr.len);
>   	rc = put_entry(buf, sizeof(u32), 1, fp);
>   	if (rc)
>   		return rc;
>   
> -	for (cur_expr = node->expr; cur_expr != NULL; cur_expr = cur_expr->next) {
> -		buf[0] = cpu_to_le32(cur_expr->expr_type);
> -		buf[1] = cpu_to_le32(cur_expr->bool);
> +	for (i = 0; i < node->expr.len; i++) {
> +		buf[0] = cpu_to_le32(node->expr.nodes[i].expr_type);
> +		buf[1] = cpu_to_le32(node->expr.nodes[i].bool);
>   		rc = put_entry(buf, sizeof(u32), 2, fp);
>   		if (rc)
>   			return rc;
> diff --git a/security/selinux/ss/conditional.h b/security/selinux/ss/conditional.h
> index 5f97f678440e..4677c6ff7450 100644
> --- a/security/selinux/ss/conditional.h
> +++ b/security/selinux/ss/conditional.h
> @@ -19,7 +19,7 @@
>    * A conditional expression is a list of operators and operands
>    * in reverse polish notation.
>    */
> -struct cond_expr {
> +struct cond_expr_node {
>   #define COND_BOOL	1 /* plain bool */
>   #define COND_NOT	2 /* !bool */
>   #define COND_OR		3 /* bool || bool */
> @@ -28,9 +28,13 @@ struct cond_expr {
>   #define COND_EQ		6 /* bool == bool */
>   #define COND_NEQ	7 /* bool != bool */
>   #define COND_LAST	COND_NEQ
> -	__u32 expr_type;
> -	__u32 bool;
> -	struct cond_expr *next;
> +	u32 expr_type;
> +	u32 bool;
> +};
> +
> +struct cond_expr {
> +	struct cond_expr_node *nodes;
> +	u32 len;
>   };
>   
>   /*
> @@ -52,7 +56,7 @@ struct cond_av_list {
>    */
>   struct cond_node {
>   	int cur_state;
> -	struct cond_expr *expr;
> +	struct cond_expr expr;
>   	struct cond_av_list true_list;
>   	struct cond_av_list false_list;
>   };