linux-kernel - [PATCH v2] dm ioct: prevent potential specter v1 gadget

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Message-Id: <20220129145839.3461330-1-jordy@pwning.systems>
Date:   Sat, 29 Jan 2022 15:58:39 +0100
From:   Jordy Zomer <jordy@...ing.systems>
To:     linux-kernel@...r.kernel.org
Cc:     Jordy Zomer <jordy@...ing.systems>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com
Subject: [PATCH v2] dm ioct: prevent potential specter v1 gadget

It appears like cmd could be a Spectre v1 gadget as it's supplied by a
user and used as an array index. Prevent the contents
of kernel memory from being leaked to userspace via speculative
execution by using array_index_nospec.

Forgot to add the nospec include, that's the reason for the v2 :)

Signed-off-by: Jordy Zomer <jordy@...ing.systems>
---
 drivers/md/dm-ioctl.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 21fe8652b095..901abd6dea41 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -18,6 +18,7 @@
 #include <linux/dm-ioctl.h>
 #include <linux/hdreg.h>
 #include <linux/compat.h>
+#include <linux/nospec.h>
 
 #include <linux/uaccess.h>
 #include <linux/ima.h>
@@ -1788,6 +1789,7 @@ static ioctl_fn lookup_ioctl(unsigned int cmd, int *ioctl_flags)
 	if (unlikely(cmd >= ARRAY_SIZE(_ioctls)))
 		return NULL;
 
+	cmd = array_index_nospec(cmd, ARRAY_SIZE(_ioctls));
 	*ioctl_flags = _ioctls[cmd].flags;
 	return _ioctls[cmd].fn;
 }
-- 
2.27.0