Commit 56c30ba7 authored Jan 29, 2018 by Dan Williams Committed by Thomas Gleixner Jan 30, 2018

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



'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

parent 2fbd7af5

include/linux/fdtable.h

+4 −1

Original line number	Diff line number	Diff line
		@@ -10,6 +10,7 @@
		#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>
		@@ -82,8 +83,10 @@ static inline struct file __fcheck_files(struct files_struct files, unsigned i
		{
		struct fdtable *fdt = rcu_dereference_raw(files->fdt);

		if (fd < fdt->max_fds)
		if (fd < fdt->max_fds) {
		fd = array_index_nospec(fd, fdt->max_fds);
		return rcu_dereference_raw(fdt->fd[fd]);
		}
		return NULL;
		}

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