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

From: tip-bot for CQ Tang
Date: Mon Mar 18 2013 - 16:07:02 EST

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)))
- if (__put_user_nocheck(c, to++, sizeof(char)))
+ if (__put_user_nocheck(c, to, sizeof(char)))

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