net: xfrm: fix shift-out-of-bounds in xfrm_get_default

Syzbot hit shift-out-of-bounds in xfrm_get_default. The problem was in
missing validation check for user data.

up->dirmask comes from user-space, so we need to check if this value
is less than XFRM_USERPOLICY_DIRMASK_MAX to avoid shift-out-of-bounds bugs.

Fixes: 2d151d39073a ("xfrm: Add possibility to set the default to block if we have no policy")
Reported-and-tested-by: syzbot+b2be9dd8ca6f6c73ee2d@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 03b66d154b2bfdc5ae63017532787f85350b56e8..4719a6d54aa62790d456b7265380f92a15e2e21c 100644 (file)
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2005,6 +2005,11 @@ static int xfrm_get_default(struct sk_buff *skb, struct nlmsghdr *nlh,
                return -EMSGSIZE;
        }
 
+       if (up->dirmask >= XFRM_USERPOLICY_DIRMASK_MAX) {
+               kfree_skb(r_skb);
+               return -EINVAL;
+       }
+
        r_up = nlmsg_data(r_nlh);
 
        r_up->action = ((net->xfrm.policy_default & (1 << up->dirmask)) >> up->dirmask);