[tip:x86/urgent] x86-64: Fix the failure case in copy_user_handle_tail()

[tip-bot for CQ Tang]

Commit-ID:  66db3feb486c01349f767b98ebb10b0c3d2d021b
Gitweb:     http://git.kernel.org/tip/66db3feb486c01349f767b98ebb10b0c3d2d021b
Author:     CQ Tang <cq.tang@xxxxxxxxx>
AuthorDate: Mon, 18 Mar 2013 11:02:21 -0400
Committer:  H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Mon, 18 Mar 2013 11:32:03 -0700

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@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20130318150221.8439.993.stgit@xxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@xxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
 arch/x86/lib/usercopy_64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
index 05928aa..906fea3 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;
 	}
 
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