selinux: check length fields in policies

In multiple places the binary policy announces how many items of some
kind are to be expected next.  Before reading them the kernel already
allocates enough memory for that announced size.  Validate that the
remaining input size can actually fit the announced items, to avoid OOM
issues on malformed binary policies.

Signed-off-by: Christian Göttsche <[email protected]>
---
v3:
  - fix error branch by returning directly instead of jumping to goto
    label, see
      https://lore.kernel.org/all/[email protected]/
  - rename to size_check()
  - add comments for magic values

security/selinux/ss/avtab.c

@@ -548,6 +548,11 @@ int avtab_read(struct avtab *a, struct policy_file *fp, struct policydb *pol)
 		goto bad;
 	}
 
+	/* avtab_read_item() reads at least 96 bytes for any valid entry */
+	rc = size_check(3 * sizeof(u32), nel, fp);
+	if (rc)
+		goto bad;
+
 	rc = avtab_alloc(a, nel);
 	if (rc)
 		goto bad;

security/selinux/ss/conditional.c

@@ -12,6 +12,7 @@
 
 #include "security.h"
 #include "conditional.h"
+#include "policydb.h"
 #include "services.h"
 
 /*
@@ -329,6 +330,11 @@ static int cond_read_av_list(struct policydb *p, struct policy_file *fp,
 	if (len == 0)
 		return 0;
 
+	/* avtab_read_item() reads at least 96 bytes for any valid entry */
+	rc = size_check(3 * sizeof(u32), len, fp);
+	if (rc)
+		return rc;
+
 	list->nodes = kcalloc(len, sizeof(*list->nodes), GFP_KERNEL);
 	if (!list->nodes)
 		return -ENOMEM;
@@ -379,6 +385,12 @@ static int cond_read_node(struct policydb *p, struct cond_node *node, struct pol
 
 	/* expr */
 	len = le32_to_cpu(buf[1]);
+
+	/* we will read 64 bytes per node */
+	rc = size_check(2 * sizeof(u32), len, fp);
+	if (rc)
+		return rc;
+
 	node->expr.nodes = kcalloc(len, sizeof(*node->expr.nodes), GFP_KERNEL);
 	if (!node->expr.nodes)
 		return -ENOMEM;
@@ -417,6 +429,11 @@ int cond_read_list(struct policydb *p, struct policy_file *fp)
 
 	len = le32_to_cpu(buf[0]);
 
+	/* cond_read_node() reads at least 128 bytes for any valid node */
+	rc = size_check(4 * sizeof(u32), len, fp);
+	if (rc)
+		return rc;
+
 	p->cond_list = kcalloc(len, sizeof(*p->cond_list), GFP_KERNEL);
 	if (!p->cond_list)
 		return -ENOMEM;

security/selinux/ss/policydb.c

@@ -1100,6 +1100,9 @@ int str_read(char **strp, gfp_t flags, struct policy_file *fp, u32 len)
 	if ((len == 0) || (len == (u32)-1))
 		return -EINVAL;
 
+	if (size_check(sizeof(char), len, fp))
+		return -EINVAL;
+
 	str = kmalloc(len + 1, flags | __GFP_NOWARN);
 	if (!str)
 		return -ENOMEM;
@@ -1174,6 +1177,11 @@ static int common_read(struct policydb *p, struct symtab *s, struct policy_file
 	if (nel > SEL_VEC_MAX)
 		goto bad;
 
+	/* perm_read() reads at least 64 bytes for any valid permission */
+	rc = size_check(2 * sizeof(u32), nel, fp);
+	if (rc)
+		goto bad;
+
 	rc = symtab_init(&comdatum->permissions, nel);
 	if (rc)
 		goto bad;
@@ -1348,6 +1356,11 @@ static int class_read(struct policydb *p, struct symtab *s, struct policy_file *
 		goto bad;
 	cladatum->value = val;
 
+	/* perm_read() reads at least 64 bytes for any valid permission */
+	rc = size_check(2 * sizeof(u32), nel, fp);
+	if (rc)
+		goto bad;
+
 	rc = symtab_init(&cladatum->permissions, nel);
 	if (rc)
 		goto bad;
@@ -1921,6 +1934,13 @@ static int range_read(struct policydb *p, struct policy_file *fp)
 
 	nel = le32_to_cpu(buf[0]);
 
+	/* we read at least 64 bytes and mls_read_range_helper() 32 bytes
+	 * for any valid range-transition
+	 */
+	rc = size_check(3 * sizeof(u32), nel, fp);
+	if (rc)
+		return rc;
+
 	rc = hashtab_init(&p->range_tr, nel);
 	if (rc)
 		return rc;
@@ -2689,6 +2709,13 @@ int policydb_read(struct policydb *p, struct policy_file *fp)
 		nprim = le32_to_cpu(buf[0]);
 		nel = le32_to_cpu(buf[1]);
 
+		/* every read_f() implementation reads at least 128 bytes
+		 * for any valid entry
+		 */
+		rc = size_check(4 * sizeof(u32), nel, fp);
+		if (rc)
+			goto out;
+
 		rc = symtab_init(&p->symtab[i], nel);
 		if (rc)
 			goto out;
@@ -2730,6 +2757,11 @@ int policydb_read(struct policydb *p, struct policy_file *fp)
 		goto bad;
 	nel = le32_to_cpu(buf[0]);
 
+	/* we read at least 96 bytes for any valid role-transition */
+	rc = size_check(3 * sizeof(u32), nel, fp);
+	if (rc)
+		goto bad;
+
 	rc = hashtab_init(&p->role_tr, nel);
 	if (rc)
 		goto bad;

security/selinux/ss/policydb.h

@@ -353,6 +353,19 @@ struct policy_data {
 	struct policy_file *fp;
 };
 
+static inline int size_check(size_t bytes, size_t num, const struct policy_file *fp)
+{
+	size_t len;
+
+	if (unlikely(check_mul_overflow(bytes, num, &len)))
+		return -EINVAL;
+
+	if (unlikely(len > fp->len))
+		return -EINVAL;
+
+	return 0;
+}
+
 static inline int next_entry(void *buf, struct policy_file *fp, size_t bytes)
 {
 	if (bytes > fp->len)