/dev/zero: avoid repeated access_ok() checks

In read_zero, we check for access_ok() once for the count bytes.  It is
unnecessarily checked again in clear_user.  Use __clear_user, which does
not check for access_ok().

Signed-off-by: Nikanth Karthikesan <knikanth@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 0aede1d..6c8b65d 100644 (file)
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -690,7 +690,7 @@ static ssize_t read_zero(struct file * file, char __user * buf,
 
                if (chunk > PAGE_SIZE)
                        chunk = PAGE_SIZE;      /* Just for latency reasons */
-               unwritten = clear_user(buf, chunk);
+               unwritten = __clear_user(buf, chunk);
                written += chunk - unwritten;
                if (unwritten)
                        break;