CVE-2026-31433: ksmbd: fix potencial OOB in get_file_all_info() for compound requests

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

ksmbd: fix potencial OOB in getfileallinfo() for compound requests

When a compound request consists of QUERYDIRECTORY + QUERYINFO (FILEALLINFORMATION) and the first command consumes nearly the entire maxtranssize, getfileallinfo() would blindly call smbConvertToUTF16() with PATHMAX, causing out-of-bounds write beyond the response buffer. In getfileallinfo(), there was a missing validation check for the client-provided OutputBufferLength before copying the filename into FileName field of the smb2fileallinfo structure. If the filename length exceeds the available buffer space, it could lead to potential buffer overflows or memory corruption during smbConvertToUTF16 conversion. This calculating the actual free buffer size using smb2calcmaxoutbuflen() and returning -EINVAL if the buffer is insufficient and updating smbConvertToUTF16 to use the actual filename length (clamped by PATHMAX) to ensure a safe copy operation.