uaccess: add missing __must_check attributes

The usercopy implementation comments describe that callers of the
copy_*_user() family of functions must always have their return values
checked.  This can be enforced at compile time with __must_check, so add
it where needed.

Link: http://lkml.kernel.org/r/201908251609.ADAD5CAAC1@keescook
Signed-off-by: Kees Cook <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Dan Carpenter <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: kees

include/linux/thread_info.h

@@ -134,7 +134,7 @@ static inline void copy_overflow(int size, unsigned long count)
 	WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
 }
 
-static __always_inline bool
+static __always_inline __must_check bool
 check_copy_size(const void *addr, size_t bytes, bool is_source)
 {
 	int sz = __compiletime_object_size(addr);

include/linux/uaccess.h

@@ -55,15 +55,15 @@
  * as usual) and both source and destination can trigger faults.
  */
 
-static __always_inline unsigned long
+static __always_inline __must_check unsigned long
 __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
 {
 	kasan_check_write(to, n);
 	check_object_size(to, n, false);
 	return raw_copy_from_user(to, from, n);
 }
 
-static __always_inline unsigned long
+static __always_inline __must_check unsigned long
 __copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	might_fault();
@@ -85,15 +85,15 @@ __copy_from_user(void *to, const void __user *from, unsigned long n)
  * The caller should also make sure he pins the user space address
  * so that we don't result in page fault and sleep.
  */
-static __always_inline unsigned long
+static __always_inline __must_check unsigned long
 __copy_to_user_inatomic(void __user *to, const void *from, unsigned long n)
 {
 	kasan_check_read(from, n);
 	check_object_size(from, n, true);
 	return raw_copy_to_user(to, from, n);
 }
 
-static __always_inline unsigned long
+static __always_inline __must_check unsigned long
 __copy_to_user(void __user *to, const void *from, unsigned long n)
 {
 	might_fault();
@@ -103,7 +103,7 @@ __copy_to_user(void __user *to, const void *from, unsigned long n)
 }
 
 #ifdef INLINE_COPY_FROM_USER
-static inline unsigned long
+static inline __must_check unsigned long
 _copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	unsigned long res = n;
@@ -117,12 +117,12 @@ _copy_from_user(void *to, const void __user *from, unsigned long n)
 	return res;
 }
 #else
-extern unsigned long
+extern __must_check unsigned long
 _copy_from_user(void *, const void __user *, unsigned long);
 #endif
 
 #ifdef INLINE_COPY_TO_USER
-static inline unsigned long
+static inline __must_check unsigned long
 _copy_to_user(void __user *to, const void *from, unsigned long n)
 {
 	might_fault();
@@ -133,7 +133,7 @@ _copy_to_user(void __user *to, const void *from, unsigned long n)
 	return n;
 }
 #else
-extern unsigned long
+extern __must_check unsigned long
 _copy_to_user(void __user *, const void *, unsigned long);
 #endif
 
@@ -222,8 +222,9 @@ static inline bool pagefault_disabled(void)
 
 #ifndef ARCH_HAS_NOCACHE_UACCESS
 
-static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
-				const void __user *from, unsigned long n)
+static inline __must_check unsigned long
+__copy_from_user_inatomic_nocache(void *to, const void __user *from,
+				  unsigned long n)
 {
 	return __copy_from_user_inatomic(to, from, n);
 }