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

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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: 2d151d3907 ("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>
This commit is contained in:
Pavel Skripkin 2021-07-28 19:38:18 +03:00 committed by Steffen Klassert
parent 2d151d3907
commit 5d8dbb7fb8
2 changed files with 7 additions and 1 deletions
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1
include/uapi/linux/xfrm.h
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@ -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;
};

7
net/xfrm/xfrm_user.c
View file

@ -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);