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

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Date:   Thu, 4 Nov 2021 00:14:31 +0800
From:   butt3rflyh4ck <butterflyhuangxx@...il.com>
To:     mostrows@...thlink.net, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Networking <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: A kernel-infoleak bug in pppoe_getname() in drivers/net/ppp/pppoe.c

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
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.


Regards,
  butt3rflyh4ck.
-- 
Active Defense Lab of Venustech

View attachment "0001-net-ppp-pppoe-fix-a-kernel-infoleak-in-pppoe_getname.patch" of type "text/x-patch" (1074 bytes)