[PATCH next] usb_string_copy: Use kzalloc() to avoid leaking old data

[david.laight.linux@gmail.com]

From: David Laight <david.laight.linux@gmail.com>

If the string is read while being updated (which is why the copy is done
in place) and the new string is longer than the old one, then the reader
can read memory that isnt part of either string.

Use memcpy() to copy the known length string instead of strcpy.

Signed-off-by: David Laight <david.laight.linux@gmail.com>
---
This is one of a group of patches that remove potentially unbounded
strcpy() calls.

They are mostly replaced by strscpy() or, when strlen() has just been
called, with memcpy() (usually including the '\0').

Calls with copy string literals into arrays are left unchanged.
They are safe and easily detected as such.

The changes were made by getting the compiler to detect the calls and
then fixing the code by hand.

Note that all the changes are only compile tested.

Some Makefiles were changed to allow files to contain strcpy().
As well as 'difficult to fix' files, this included 'show' functions
as they really need to use sysfs_emit() or seq_printf().

All the patches are being sent individually to avoid very long cc lists.
Apologies for the terse commit messages and likely unexpected tags.
(There are about 100 patches in total.)

 drivers/usb/gadget/configfs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
index 183a25f65ac8..4518dc6bb5af 100644
--- a/drivers/usb/gadget/configfs.c
+++ b/drivers/usb/gadget/configfs.c
@@ -125,11 +125,11 @@ static int usb_string_copy(const char *s, char **s_copy)
 	if (copy) {
 		str = copy;
 	} else {
-		str = kmalloc(USB_MAX_STRING_WITH_NULL_LEN, GFP_KERNEL);
+		str = kzalloc(USB_MAX_STRING_WITH_NULL_LEN, GFP_KERNEL);
 		if (!str)
 			return -ENOMEM;
 	}
-	strcpy(str, s);
+	memcpy(str, s, ret + 1);
 	if (str[ret - 1] == '\n')
 		str[ret - 1] = '\0';
 	*s_copy = str;
-- 
2.39.5