dm ioctl: prevent stack leak in dm ioctl call

commit 4617f564c06117c7d1b611be49521a4430042287 upstream.

When calling a dm ioctl that doesn't process any data
(IOCTL_FLAGS_NO_PARAMS), the contents of the data field in struct
dm_ioctl are left initialized.  Current code is incorrectly extending
the size of data copied back to user, causing the contents of kernel
stack to be leaked to user.  Fix by only copying contents before data
and allow the functions processing the ioctl to override.

Signed-off-by: Adrian Salido <salidoa@google.com>
Reviewed-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 51521429fb59d01ea65e8d1243a1151272f9beca..d20c2de3fd72068015ade0de702014052b9810d8 100644 (file)
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1839,7 +1839,7 @@ static int ctl_ioctl(uint command, struct dm_ioctl __user *user)
        if (r)
                goto out;
 
-       param->data_size = sizeof(*param);
+       param->data_size = offsetof(struct dm_ioctl, data);
        r = fn(param, input_param_size);
 
        if (unlikely(param->flags & DM_BUFFER_FULL_FLAG) &&