From: Dan Williams <dan.j.williams@intel.com>
Date: Tue, 30 Jan 2018 01:03:05 +0000 (-0800)
Subject: vfs, fdtable: Prevent bounds-check bypass via speculative execution
X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=b2fddb5b3cbe2ac7d18e62c9588a6cbee9cd7383

vfs, fdtable: Prevent bounds-check bypass via speculative execution

commit 56c30ba7b348b90484969054d561f711ba196507 upstream.

'fd' is a user controlled value that is used as a data dependency to
read from the 'fdt->fd' array.  In order to avoid potential leaks of
kernel memory values, block speculative execution of the instruction
stream that could issue reads based on an invalid 'file *' returned from
__fcheck_files.

Co-developed-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: kernel-hardening@lists.openwall.com
Cc: gregkh@linuxfoundation.org
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: torvalds@linux-foundation.org
Cc: alan@linux.intel.com
Link: https://lkml.kernel.org/r/151727418500.33451.17392199002892248656.stgit@dwillia2-desk3.amr.corp.intel.com
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index 82163c4b32c9..5a14de6a6f62 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -9,6 +9,7 @@
 #include <linux/compiler.h>
 #include <linux/spinlock.h>
 #include <linux/rcupdate.h>
+#include <linux/nospec.h>
 #include <linux/types.h>
 #include <linux/init.h>
 #include <linux/fs.h>
@@ -85,8 +86,10 @@ static inline struct file * fcheck_files(struct files_struct *files, unsigned in
 	struct file * file = NULL;
 	struct fdtable *fdt = files_fdtable(files);
 
-	if (fd < fdt->max_fds)
+	if (fd < fdt->max_fds) {
+		fd = array_index_nospec(fd, fdt->max_fds);
 		file = rcu_dereference_check_fdtable(files, fdt->fd[fd]);
+	}
 	return file;
 }