vfs, fdtable: Prevent bounds-check bypass via speculative execution
authorDan Williams <dan.j.williams@intel.com>
Tue, 30 Jan 2018 01:03:05 +0000 (17:03 -0800)
committerBen Hutchings <ben@decadent.org.uk>
Mon, 19 Mar 2018 18:58:37 +0000 (18:58 +0000)
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

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>

index 82163c4..5a14de6 100644 (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>
@@ -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;