dm ioctl: prevent stack leak in dm ioctl call

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.

Cc: stable@vger.kernel.org
Signed-off-by: Adrian Salido <salidoa@google.com>
Reviewed-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 0956b86593603470ab6c27e0ae69af430e01708c..ddda8107aa7e3dfaf3d662b570f9baeb57bb183f 100644 (file)
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1840,7 +1840,7 @@ 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) &&