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

[butt3rflyh4ck]

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
From 5a2d0282931967dc9d90248221b3120e1e33551c Mon Sep 17 00:00:00 2001
From: Xiaolong Huang <butterflyhuangxx@xxxxxxxxx>
Date: Wed, 3 Nov 2021 23:33:55 +0800
Subject: [PATCH] net: ppp: pppoe: fix a kernel-infoleak in pppoe_getname()

The struct sockaddr_pppox has a 2-byte hole, and pppoe_getname() currently
does not clear it before copying kernel data to user space.

Signed-off-by: Xiaolong Huang <butterflyhuangxx@xxxxxxxxx>
---
 drivers/net/ppp/pppoe.c | 5 +++++
 1 file changed, 5 insertions(+)

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,
-- 
2.25.1