[PATCH 3.16 272/346] asm-generic: make get_user() clear the destination on errors

[Ben Hutchings]

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

commit 9ad18b75c2f6e4a78ce204e79f37781f8815c0fa upstream.

both for access_ok() failures and for faults halfway through

Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 include/asm-generic/uaccess.h | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/include/asm-generic/uaccess.h
+++ b/include/asm-generic/uaccess.h
@@ -228,14 +228,18 @@ extern int __put_user_bad(void) __attrib
 	might_fault();						\
 	access_ok(VERIFY_READ, ptr, sizeof(*ptr)) ?		\
 		__get_user(x, ptr) :				\
-		-EFAULT;					\
+		((x) = (__typeof__(*(ptr)))0,-EFAULT);		\
 })
 
 #ifndef __get_user_fn
 static inline int __get_user_fn(size_t size, const void __user *ptr, void *x)
 {
-	size = __copy_from_user(x, ptr, size);
-	return size ? -EFAULT : size;
+	size_t n = __copy_from_user(x, ptr, size);
+	if (unlikely(n)) {
+		memset(x + (size - n), 0, n);
+		return -EFAULT;
+	}
+	return 0;
 }
 
 #define __get_user_fn(sz, u, k)	__get_user_fn(sz, u, k)