net: fix info leak in compat dev_ifconf()

The implementation of dev_ifconf() for the compat ioctl interface uses
an intermediate ifc structure allocated in userland for the duration of
the syscall. Though, it fails to initialize the padding bytes inserted
for alignment and that for leaks four bytes of kernel stack. Add an
explicit memset(0) before filling the structure to avoid the info leak.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/socket.c b/net/socket.c
index dfe5b66c97e0bc836efed43ad080dec620301306..a5471f804d994ece8c31df6be0e04d5076b6dfd0 100644 (file)
--- a/net/socket.c
+++ b/net/socket.c
@@ -2657,6 +2657,7 @@ static int dev_ifconf(struct net *net, struct compat_ifconf __user *uifc32)
        if (copy_from_user(&ifc32, uifc32, sizeof(struct compat_ifconf)))
                return -EFAULT;
 
+       memset(&ifc, 0, sizeof(ifc));
        if (ifc32.ifcbuf == 0) {
                ifc32.ifc_len = 0;
                ifc.ifc_len = 0;