x86-64: Fix the failure case in copy_user_handle_tail()

The increment of "to" in copy_user_handle_tail() will have incremented
before a failure has been noted.  This causes us to skip a byte in the
failure case.

Only do the increment when assured there is no failure.

Signed-off-by: CQ Tang <cq.tang@intel.com>
Link: http://lkml.kernel.org/r/20130318150221.8439.993.stgit@phlsvslse11.ph.intel.com
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@vger.kernel.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 05928aae911e..906fea315791 100644
--- a/arch/x86/lib/usercopy_64.c
+++ b/arch/x86/lib/usercopy_64.c
@@ -74,10 +74,10 @@ copy_user_handle_tail(char *to, char *from, unsigned len, unsigned zerorest)
         char c;
         unsigned zero_len;
 
-        for (; len; --len) {
+        for (; len; --len, to++) {
                 if (__get_user_nocheck(c, from++, sizeof(char)))
                         break;
-                if (__put_user_nocheck(c, to++, sizeof(char)))
+                if (__put_user_nocheck(c, to, sizeof(char)))
                         break;
         }