autofs: harden 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@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Ian Kent <raven@themaw.net>
Link: https://lkml.kernel.org/r/20200818122203.GO17456@casper.infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/autofs/dev-ioctl.c b/fs/autofs/dev-ioctl.c
index 75105f4..322b7df 100644 (file)
--- 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 @@ out:
 
 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 */