2021-09-02 19:07:33

by Pavel Skripkin

Subject: [PATCH] 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: [email protected]
Signed-off-by: Pavel Skripkin <[email protected]>
---
net/xfrm/xfrm_user.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index b7b986520dc7..e4cf48c71315 100644
--- 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);
--
2.33.0

2021-09-10 10:02:04

by Steffen Klassert

Subject: Re: [PATCH] net: xfrm: fix shift-out-of-bounds in xfrm_get_default

On Thu, Sep 02, 2021 at 10:04:00PM +0300, Pavel Skripkin wrote:
> 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: [email protected]
> Signed-off-by: Pavel Skripkin <[email protected]>

Applied, thanks Pavel!