USB: gadget: u_f: add overflow checks to VLA macros

size can potentially hold an overflowed value if its assigned expression
is left unchecked, leading to a smaller than needed allocation when
vla_group_size() is used by callers to allocate memory.
To fix this, add a test for saturation before declaring variables and an
overflow check to (n) * sizeof(type).
If the expression results in overflow, vla_group_size() will return SIZE_MAX.
Reported-by: Ilja Van Sprundel <ivansprundel@ioactive.com>
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Brooke Basile <brookebasile@gmail.com>
Acked-by: Felipe Balbi <balbi@kernel.org>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/u_f.h

@@ -14,6 +14,7 @@
 #define __U_F_H__
 
 #include <linux/usb/gadget.h>
+#include <linux/overflow.h>
 
 /* Variable Length Array Macros **********************************************/
 #define vla_group(groupname) size_t groupname##__next = 0
@@ -21,20 +22,35 @@
 
 #define vla_item(groupname, type, name, n) \
 	size_t groupname##_##name##__offset = ({			       \
+		size_t offset = 0;					       \
+		if (groupname##__next != SIZE_MAX) {			       \
 			size_t align_mask = __alignof__(type) - 1;	       \
-		size_t offset = (groupname##__next + align_mask) & ~align_mask;\
-		size_t size = (n) * sizeof(type);			       \
-		groupname##__next = offset + size;			       \
+			size_t offset = (groupname##__next + align_mask)       \
+					 & ~align_mask;			       \
+			size_t size = array_size(n, sizeof(type));	       \
+			if (check_add_overflow(offset, size,		       \
+					       &groupname##__next)) {          \
+				groupname##__next = SIZE_MAX;		       \
+				offset = 0;				       \
+			}						       \
+		}							       \
 		offset;							       \
 	})
 
 #define vla_item_with_sz(groupname, type, name, n) \
-	size_t groupname##_##name##__sz = (n) * sizeof(type);		       \
+	size_t groupname##_##name##__sz = array_size(n, sizeof(type));	        \
 	size_t groupname##_##name##__offset = ({			        \
+		size_t offset = 0;						\
+		if (groupname##__next != SIZE_MAX) {				\
 			size_t align_mask = __alignof__(type) - 1;		\
-		size_t offset = (groupname##__next + align_mask) & ~align_mask;\
-		size_t size = groupname##_##name##__sz;			       \
-		groupname##__next = offset + size;			       \
+			size_t offset = (groupname##__next + align_mask)	\
+					 & ~align_mask;				\
+			if (check_add_overflow(offset, groupname##_##name##__sz,\
+							&groupname##__next)) {	\
+				groupname##__next = SIZE_MAX;			\
+				offset = 0;					\
+			}							\
+		}								\
 		offset;								\
 	})