usb: gadget: configfs: Prevent OOB read/write in usb_string_copy()

Userspace provided string 's' could trivially have the length zero. Left
unchecked this will firstly result in an OOB read in the form
`if (str[0 - 1] == '\n') followed closely by an OOB write in the form
`str[0 - 1] = '\0'`.

There is already a validating check to catch strings that are too long.
Let's supply an additional check for invalid strings that are too short.

Signed-off-by: Lee Jones <lee@kernel.org>
Cc: stable <stable@kernel.org>
Link: https://lore.kernel.org/r/20240705074339.633717-1-lee@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
index ce3cfa1f36f516d117e0095a4ab47a0abd9b5c48..0e7c1e947c0a0e4d84797c319168ebe45fd98c54 100644 (file)
--- a/drivers/usb/gadget/configfs.c
+++ b/drivers/usb/gadget/configfs.c
@@ -115,9 +115,12 @@ static int usb_string_copy(const char *s, char **s_copy)
        int ret;
        char *str;
        char *copy = *s_copy;
+
        ret = strlen(s);
        if (ret > USB_MAX_STRING_LEN)
                return -EOVERFLOW;
+       if (ret < 1)
+               return -EINVAL;
 
        if (copy) {
                str = copy;