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

commit 66db3feb486c01349f767b98ebb10b0c3d2d021b upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 05928aae911e0addaaaf1bd0fce5002ba3c9f96e..906fea3157919dcffabfe2bc4b23a1becb98aa7c 100644 (file)
--- 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;
        }