Re: A kernel-infoleak bug in pppoe_getname() in drivers/net/ppp/pppoe.c

From: Jakub Kicinski
Date: Wed Nov 03 2021 - 12:53:12 EST


On Thu, 4 Nov 2021 00:14:31 +0800 butt3rflyh4ck wrote:
> Hi, I report a kernel-infoleak bug in pppoe_getname()) in
> drivers/net/ppp/pppoe.c.
> And we can call getname ioctl to invoke pppoe_getname().
>
> ###anaylze
> ```
> static int pppoe_getname(struct socket *sock, struct sockaddr *uaddr,
> int peer)
> {
> int len = sizeof(struct sockaddr_pppox);
> struct sockaddr_pppox sp; ///---> define a 'sp' in stack but does
> not clear it
>
> sp.sa_family = AF_PPPOX; ///---> sp.sa_family is a short type, just

But the structure is marked as __packed.

> 2 byte sizes.
> sp.sa_protocol = PX_PROTO_OE;
> memcpy(&sp.sa_addr.pppoe, &pppox_sk(sock->sk)->pppoe_pa,
> sizeof(struct pppoe_addr));
>
> memcpy(uaddr, &sp, len);
>
> return len;
> }
> ```
> There is an anonymous 2-byte hole after sa_family, make sure to clear it.
>
> ###fix
> use memset() to clear the struct sockaddr_pppox sp.
> ```
> diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
> index 3619520340b7..fec328ad7202 100644
> --- a/drivers/net/ppp/pppoe.c
> +++ b/drivers/net/ppp/pppoe.c
> @@ -723,6 +723,11 @@ static int pppoe_getname(struct socket *sock,
> struct sockaddr *uaddr,
> int len = sizeof(struct sockaddr_pppox);
> struct sockaddr_pppox sp;
>
> + /* There is an anonymous 2-byte hole after sa_family,
> + * make sure to clear it.
> + */
> + memset(&sp, 0, len);
> +
> sp.sa_family = AF_PPPOX;
> sp.sa_protocol = PX_PROTO_OE;
> memcpy(&sp.sa_addr.pppoe, &pppox_sk(sock->sk)->pppoe_pa,
> ```
> The attachment is a patch.