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

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: 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.

References

• https://git.kernel.org/stable/c/a444c3fc264119801575ab086e03fb4952f23fd0
• https://git.kernel.org/stable/c/c95fbdde87e39e5e0ae27f28bf6711edfb985caa
• https://git.kernel.org/stable/c/e8474a10c535e6a2024c3b06e37e4a3a23beb490
• https://git.kernel.org/stable/c/72b8ee0d9826e8ed00e0bdfce3e46b98419b37ce
• https://git.kernel.org/stable/c/2d16f63d8030903e5031853e79d731ee5d474e70
• https://git.kernel.org/stable/c/d1205033e912f9332c1dbefa812e6ceb0575ce0a
• https://git.kernel.org/stable/c/eecfefad0953b2f31aaefa058f7f348ff39c4bba
• https://git.kernel.org/stable/c/6d3c721e686ea6c59e18289b400cc95c76e927e0