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Date: Mon, 12 Mar 2018 03:03:34 +0000
From: Ben Hutchings <>
 "Al Viro" <>,,
 "Thomas Gleixner" <>,
 "Dan Williams" <>,,,
Subject: [PATCH 3.2 088/104] vfs, fdtable: Prevent bounds-check bypass via
 speculative execution

3.2.101-rc1 review patch.  If anyone has any objections, please let me know.


From: Dan Williams <>

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 <>
Signed-off-by: Dan Williams <>
Signed-off-by: Thomas Gleixner <>
Cc: Al Viro <>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <>
 include/linux/fdtable.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- 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 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;

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