ksmbd: validate compression Flags before kvmalloc

ksmbd: validate compression Flags before kvmalloc

ksmbd_decompress_request() allocated the decompressed request buffer
before smb_compression_decompress() rejected unknown transform Flags or
chained mode when it was not negotiated. A remote peer could force a
transient multi-megabyte allocation that was immediately freed on
-EINVAL.

Validate CHAINED/NONE Flags and compress_chained before kvmalloc.

Link: https://github.com/namjaejeon/ksmbd/issues/529
Fixes: a08de24c2b85 ("ksmbd: negotiate and decode SMB2 compression")
Signed-off-by: Anatolii Shumak <anatoliy.shumak@gmail.com>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>