net: xfrm: fix shift-out-of-bounce

We need to check up->dirmask to avoid shift-out-of-bounce bug,
since up->dirmask comes from userspace.

Also, added XFRM_USERPOLICY_DIRMASK_MAX constant to uapi to inform
user-space that up->dirmask has maximum possible value

Fixes: 2d151d39073a ("xfrm: Add possibility to set the default to block if we have no policy")
Reported-and-tested-by: syzbot+9cd5837a045bbee5b810@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
index 6e80951..b96c1ea 100644 (file)
--- a/include/uapi/linux/xfrm.h
+++ b/include/uapi/linux/xfrm.h
@@ -514,6 +514,7 @@ struct xfrm_user_offload {
 #define XFRM_OFFLOAD_INBOUND   2
 
 struct xfrm_userpolicy_default {
+#define XFRM_USERPOLICY_DIRMASK_MAX    (sizeof(__u8) * 8)
        __u8                            dirmask;
        __u8                            action;
 };

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index 4eafd11..127c99f 100644 (file)
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -1966,9 +1966,14 @@ static int xfrm_set_default(struct sk_buff *skb, struct nlmsghdr *nlh,
 {
        struct net *net = sock_net(skb->sk);
        struct xfrm_userpolicy_default *up = nlmsg_data(nlh);
-       u8 dirmask = (1 << up->dirmask) & XFRM_POL_DEFAULT_MASK;
+       u8 dirmask;
        u8 old_default = net->xfrm.policy_default;
 
+       if (up->dirmask >= XFRM_USERPOLICY_DIRMASK_MAX)
+               return -EINVAL;
+
+       dirmask = (1 << up->dirmask) & XFRM_POL_DEFAULT_MASK;
+
        net->xfrm.policy_default = (old_default & (0xff ^ dirmask))
                                    | (up->action << up->dirmask);