net: fix info leak in compat dev_ifconf()

commit 43da5f2e0d0c69ded3d51907d9552310a6b545e8 upstream.

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>
[bwh: Backported to 2.6.32: adjust filename, context]
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/fs/compat_ioctl.c b/fs/compat_ioctl.c
index 0dd21a425973272b88b3f89fd0a7bd654ef29b78..98d3c581a4bc5b972296f6050f53ab3550f2c848 100644 (file)
--- a/fs/compat_ioctl.c
+++ b/fs/compat_ioctl.c
@@ -352,6 +352,7 @@ static int dev_ifconf(unsigned int fd, unsigned int cmd, unsigned long arg)
        if (copy_from_user(&ifc32, compat_ptr(arg), sizeof(struct ifconf32)))
                return -EFAULT;
 
+       memset(&ifc, 0, sizeof(ifc));
        if (ifc32.ifcbuf == 0) {
                ifc32.ifc_len = 0;
                ifc.ifc_len = 0;