2021-07-28 16:40:25

by Pavel Skripkin

Subject: [PATCH next] 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: [email protected]
Signed-off-by: Pavel Skripkin <[email protected]>
---
include/uapi/linux/xfrm.h | 1 +
net/xfrm/xfrm_user.c | 7 ++++++-
2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
index 6e8095106192..b96c1ea7166d 100644
--- 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 acc3a0dab331..03b66d154b2b 100644
--- 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);

--
2.32.0

2021-08-02 05:53:15

by Steffen Klassert

Subject: Re: [PATCH next] net: xfrm: fix shift-out-of-bounce

On Wed, Jul 28, 2021 at 07:38:18PM +0300, Pavel Skripkin wrote:
> 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: [email protected]
> Signed-off-by: Pavel Skripkin <[email protected]>

Applied, thanks a lot!