[RFC] fs/kcore: change copy_to_user to copy_in_user

[yalin wang <yalin.wang2010@gmail.com>]

the copy_to_user() here expect can fix the fault on both kernel and
user address, this is not true on other platforms except x86,
change to user copy_in_user() so that can detect the page fault,
work as expected.

Signed-off-by: yalin wang <yalin.wang2010@gmail.com>
---
 fs/proc/kcore.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 92e6726..4f28deb 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c
@@ -515,8 +515,12 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		} else {
 			if (kern_addr_valid(start)) {
 				unsigned long n;
-
-				n = copy_to_user(buffer, (char *)start, tsz);
+				if ((start + tsz < tsz) ||
+						(start + tsz) > TASK_SIZE)
+					return -EFAULT;
+				set_fs(KERNEL_DS);
+				n = copy_in_user(buffer, (char *)start, tsz);
+				set_fs(USER_DS);
 				/*
 				 * We cannot distinguish between fault on source
 				 * and fault on destination. When this happens
-- 
1.9.1