linux-kernel - [PATCH 4.9 9/9] dm ioctl: prevent stack leak in dm ioctl call

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Message-Id: <20170506203835.294057976@linuxfoundation.org>
Date:   Sat,  6 May 2017 13:39:30 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Adrian Salido <salidoa@...gle.com>,
        Alasdair G Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 4.9 9/9] dm ioctl: prevent stack leak in dm ioctl call

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Adrian Salido <salidoa@...gle.com>

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@...gle.com>
Reviewed-by: Alasdair G Kergon <agk@...hat.com>
Signed-off-by: Mike Snitzer <snitzer@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/dm-ioctl.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1847,7 +1847,7 @@ static int ctl_ioctl(uint command, struc
 	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) &&