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 <li...@rasmusvillemoes.dk> --- 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