I noticed that offsetof(struct filename, iname) is actually 28 on 64
bit platforms, so we always pass an unaligned pointer to
strncpy_from_user. This is mostly a problem for those 64 bit platforms
without HAVE_EFFICIENT_UNALIGNED_ACCESS, but even on x86_64, unaligned
accesses carry a penalty, especially when done in a loop.
Let's try to ensure we always pass an aligned destination pointer to
strncpy_from_user. I considered making refcnt a long instead of doing
the union thing, and mostly ended up tossing a coin.
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
---
Cc'ing Linus, not because it's urgent in any way, but because he's
usually interested in strncpy_from_user and he can probably tell me
why this is completely immaterial.
fs/namei.c | 2 ++
include/linux/fs.h | 5 ++++-
2 files changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/namei.c b/fs/namei.c
index f624d132e01e..bd150fa799a2 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -35,6 +35,7 @@
#include <linux/fs_struct.h>
#include <linux/posix_acl.h>
#include <linux/hash.h>
+#include <linux/bug.h>
#include <asm/uaccess.h>
#include "internal.h"
@@ -127,6 +128,7 @@ getname_flags(const char __user *filename, int flags, int *empty)
struct filename *result;
char *kname;
int len;
+ BUILD_BUG_ON(offsetof(struct filename, iname) % sizeof(long) != 0);
result = audit_reusename(filename);
if (result)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ae681002100a..d522e6391855 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2245,7 +2245,10 @@ struct filename {
const char *name; /* pointer to actual string */
const __user char *uptr; /* original userland pointer */
struct audit_names *aname;
- int refcnt;
+ union {
+ int refcnt;
+ long __padding;
+ };
const char iname[];
};
--
2.1.4
--
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