linux-kernel - [PATCH] Harden autofs ioctl table

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Date:   Tue, 18 Aug 2020 13:22:03 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Ian Kent <raven@...maw.net>, autofs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] Harden autofs ioctl table

The table of ioctl functions should be marked const in order to put them
in read-only memory, and we should use array_index_nospec() to avoid
speculation disclosing the contents of kernel memory to userspace.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>

diff --git a/fs/autofs/dev-ioctl.c b/fs/autofs/dev-ioctl.c
index 75105f45c51a..322b7dfb4ea0 100644
--- a/fs/autofs/dev-ioctl.c
+++ b/fs/autofs/dev-ioctl.c
@@ -8,6 +8,7 @@
 #include <linux/compat.h>
 #include <linux/syscalls.h>
 #include <linux/magic.h>
+#include <linux/nospec.h>
 
 #include "autofs_i.h"
 
@@ -563,7 +564,7 @@ static int autofs_dev_ioctl_ismountpoint(struct file *fp,
 
 static ioctl_fn lookup_dev_ioctl(unsigned int cmd)
 {
-	static ioctl_fn _ioctls[] = {
+	static const ioctl_fn _ioctls[] = {
 		autofs_dev_ioctl_version,
 		autofs_dev_ioctl_protover,
 		autofs_dev_ioctl_protosubver,
@@ -581,7 +582,10 @@ static ioctl_fn lookup_dev_ioctl(unsigned int cmd)
 	};
 	unsigned int idx = cmd_idx(cmd);
 
-	return (idx >= ARRAY_SIZE(_ioctls)) ? NULL : _ioctls[idx];
+	if (idx >= ARRAY_SIZE(_ioctls))
+		return NULL;
+	idx = array_index_nospec(idx, ARRAY_SIZE(_ioctls));
+	return _ioctls[idx];
 }
 
 /* ioctl dispatcher */