Re: [PATCH 5.10.y v2] SUNRPC: Copy the deferred RPC Call from the head buffer

[Bjoern Doebel <doebel@amazon.de>]

Hi Sasha,

thanks for raising this. I sent a v3 earlier in this thread ([PATCH
5.10.y v3]) that reworks the backport instead of applying the upstream
mechanics.

The short version: on 5.10, header parsing advances rq_arg.head[0]
via svc_getnl() without updating xdr_buf::len, so
rq_arg.len > head[0].iov_len for every Call at svc_defer() time. The
upstream guard would refuse every deferral, and copying from
head[0].iov_base would drop the headers svc_deferred_recv() expects.
v3 therefore keeps the skip-based snapshot and refuses deferral only
once a GSS integrity/privacy unwrap has run (rq_auth_slack != 0) or
when len < head[0].iov_len, since gss_unwrap_kerberos_v2() resets
buf->len.

The same rework applies to 5.15 and 6.1. The assumption upstream relies
on only holds since header parsing moved to xdr_stream in v6.3
(163cdfca341b7, "SUNRPC: Decode most of RPC header with xdr_stream");
5.15 and 6.1 still use svc_getnl(). I see the verbatim patch is
already queued for both trees - it will refuse all deferrals there,
just like my v2 would have on 5.10.

Want me to send v3-style backports for 5.15.y and 6.1.y?

Best regards,
Bjoern