[PATCH 4.15 41/60] vfs, fdtable: Prevent bounds-check bypass via speculative execution
From: Greg Kroah-Hartman
Date: Mon Feb 05 2018 - 13:53:46 EST
4.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Dan Williams dan.j.williams@xxxxxxxxx
commit 56c30ba7b348b90484969054d561f711ba196507
'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@xxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: kernel-hardening@xxxxxxxxxxxxxxxxxx
Cc: gregkh@xxxxxxxxxxxxxxxxxxx
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: torvalds@xxxxxxxxxxxxxxxxxxxx
Cc: alan@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/151727418500.33451.17392199002892248656.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/fdtable.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -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_file
{
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;
}