auditsc: audit_krule mask accesses need bounds checking

Fixes an easy DoS and possible information disclosure.

This does nothing about the broken state of x32 auditing.

eparis: If the admin has enabled auditd and has specifically loaded
audit rules.  This bug has been around since before git.  Wow...

Cc: stable@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 9 deletions

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index f251a5e8d17a..21eae3c05ec0 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -728,6 +728,22 @@ static enum audit_state audit_filter_task(struct task_struct *tsk, char **key)
         return AUDIT_BUILD_CONTEXT;
 }
 
+static int audit_in_mask(const struct audit_krule *rule, unsigned long val)
+{
+        int word, bit;
+
+        if (val > 0xffffffff)
+                return false;
+
+        word = AUDIT_WORD(val);
+        if (word >= AUDIT_BITMASK_SIZE)
+                return false;
+
+        bit = AUDIT_BIT(val);
+
+        return rule->mask[word] & bit;
+}
+
 /* At syscall entry and exit time, this filter is called if the
  * audit_state is not low enough that auditing cannot take place, but is
  * also not high enough that we already know we have to write an audit
@@ -745,11 +761,8 @@ static enum audit_state audit_filter_syscall(struct task_struct *tsk,
 
         rcu_read_lock();
         if (!list_empty(list)) {
-                int word = AUDIT_WORD(ctx->major);
-                int bit  = AUDIT_BIT(ctx->major);
-
                 list_for_each_entry_rcu(e, list, list) {
-                        if ((e->rule.mask[word] & bit) == bit &&
+                        if (audit_in_mask(&e->rule, ctx->major) &&
                             audit_filter_rules(tsk, &e->rule, ctx, NULL,
                                                &state, false)) {
                                 rcu_read_unlock();
@@ -769,20 +782,16 @@ static enum audit_state audit_filter_syscall(struct task_struct *tsk,
 static int audit_filter_inode_name(struct task_struct *tsk,
                                    struct audit_names *n,
                                    struct audit_context *ctx) {
-        int word, bit;
         int h = audit_hash_ino((u32)n->ino);
         struct list_head *list = &audit_inode_hash[h];
         struct audit_entry *e;
         enum audit_state state;
 
-        word = AUDIT_WORD(ctx->major);
-        bit  = AUDIT_BIT(ctx->major);
-
         if (list_empty(list))
                 return 0;
 
         list_for_each_entry_rcu(e, list, list) {
-                if ((e->rule.mask[word] & bit) == bit &&
+                if (audit_in_mask(&e->rule, ctx->major) &&
                     audit_filter_rules(tsk, &e->rule, ctx, n, &state, false)) {
                         ctx->current_state = state;
                         return 1;