[PATCH 7.1 006/228] selinux: reject a permission value exceeding the class permission count

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bryam Vargas <[email protected]>

commit d14b5d0e97fccd27974fedc03b903408872907fd upstream.

perm_read() bounds a permission value by SEL_VEC_MAX but never by the
nprim of the owning class or common, which is taken verbatim from the
policy image.  security_get_permissions() then writes perms[value - 1]
into an nprim-sized kcalloc() array, so a class declaring fewer
permissions than its largest permission value drives an out-of-bounds
heap write.  The top-level symbol tables are validated this way; the
nested per-class permission table is not.

Reject a permission whose value exceeds nprim, which is already set when
perm_read() runs.  Well-formed policies are unaffected.

Cc: [email protected]
Fixes: 55fcf09b3fe4 ("selinux: add support for querying object classes and permissions from the running policy")
Signed-off-by: Bryam Vargas <[email protected]>
Acked-by: Stephen Smalley <[email protected]>
[PM: tweak comment for line length]
Signed-off-by: Paul Moore <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 security/selinux/ss/policydb.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/security/selinux/ss/policydb.c
+++ b/security/selinux/ss/policydb.c
@@ -1167,6 +1167,9 @@ static int perm_read(struct policydb *p,
 	rc = symtab_insert(s, key, perdatum);
 	if (rc)
 		goto bad;
+	/* indexes an nprim-sized array in security_get_permissions() */
+	if (perdatum->value > s->nprim)
+		goto bad;
 
 	return 0;
 bad: