asm-generic: make copy_from_user() zero the destination properly

commit 2545e5da080b4839dd859e3b09343a884f6ab0e3 upstream.

... in all cases, including the failing access_ok()

Note that some architectures using asm-generic/uaccess.h have
__copy_from_user() not zeroing the tail on failure halfway
through.  This variant works either way.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/include/asm-generic/uaccess.h b/include/asm-generic/uaccess.h
index ac68c99..61dada2 100644 (file)
--- a/include/asm-generic/uaccess.h
+++ b/include/asm-generic/uaccess.h
@@ -243,11 +243,13 @@ extern int __get_user_bad(void) __attribute__((noreturn));
 static inline long copy_from_user(void *to,
                const void __user * from, unsigned long n)
 {
+       unsigned long res = n;
        might_sleep();
-       if (access_ok(VERIFY_READ, from, n))
-               return __copy_from_user(to, from, n);
-       else
-               return n;
+       if (likely(access_ok(VERIFY_READ, from, n)))
+               res = __copy_from_user(to, from, n);
+       if (unlikely(res))
+               memset(to + (n - res), 0, res);
+       return res;
 }
 
 static inline long copy_to_user(void __user *to,