smb: smb2pdu.h: Use static_assert() to check struct sizes

JIRA: https://issues.redhat.com/browse/RHEL-57983

commit 5b4f3af
Author: Gustavo A. R. Silva <gustavoars@kernel.org>
Date:   Thu Aug 8 16:04:04 2024 -0600

    smb: smb2pdu.h: Use static_assert() to check struct sizes
    
    Commit 9f9bef9 ("smb: smb2pdu.h: Avoid -Wflex-array-member-not-at-end
    warnings") introduced tagged `struct create_context_hdr`. We want to
    ensure that when new members need to be added to the flexible structure,
    they are always included within this tagged struct.
    
    So, we use `static_assert()` to ensure that the memory layout for
    both the flexible structure and the tagged struct is the same after
    any changes.
    
    Acked-by: Namjae Jeon <linkinjeon@kernel.org>
    Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
    Signed-off-by: Steve French <stfrench@microsoft.com>

Signed-off-by: Paulo Alcantara <paalcant@redhat.com>

Author: pcacjr

fs/smb/common/smb2pdu.h

@@ -1178,6 +1178,8 @@ struct create_context {
 	);
 	__u8 Buffer[];
 } __packed;
+static_assert(offsetof(struct create_context, Buffer) == sizeof(struct create_context_hdr),
+	      "struct member likely outside of __struct_group()");
 
 struct smb2_create_req {
 	struct smb2_hdr hdr;