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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.

Change-Id: I148b33be036906d37393e49391d9181e5449f061
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.stgi
t@dwillia2-desk3.amr.corp.intel.com
This commit is contained in:
Dan Williams 2018-06-04 09:32:02 +02:00 committed by syphyr
parent 31e0724ee2
commit 63c3562e8d
1 changed files with 4 additions and 1 deletions
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5
include/linux/fdtable.h
View File

@ -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>
@ -79,8 +80,10 @@ 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;
}