Re: [PATCH v2 2/2] SUNRPC: Fix the svc_deferred_event trace class

[Trond Myklebust <trondmy@hammerspace.com>]

On Wed, 2022-04-06 at 14:08 -0400, Chuck Lever wrote:
> Fix a NULL deref crash that occurs when an svc_rqst is deferred
> while the sunrpc tracing subsystem is enabled. svc_revisit() sets
> dr->xprt to NULL, so it can't be relied upon in the tracepoint to
> provide the remote's address.
> 
> Since __sockaddr() and friends are not available before v5.18, this
> is just a partial revert of commit ece200ddd54b ("sunrpc: Save
> remote presentation address in svc_xprt for trace events") in order
> to enable backports of the fix. It can be cleaned up during a
> future merge window.
> 
> Fixes: ece200ddd54b ("sunrpc: Save remote presentation address in
> svc_xprt for trace events")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  include/trace/events/sunrpc.h |    9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/include/trace/events/sunrpc.h
> b/include/trace/events/sunrpc.h
> index ab8ae1f6ba84..4abc2fddd3b8 100644
> --- a/include/trace/events/sunrpc.h
> +++ b/include/trace/events/sunrpc.h
> @@ -2017,18 +2017,19 @@ DECLARE_EVENT_CLASS(svc_deferred_event,
>         TP_STRUCT__entry(
>                 __field(const void *, dr)
>                 __field(u32, xid)
> -               __string(addr, dr->xprt->xpt_remotebuf)
> +               __dynamic_array(u8, addr, dr->addrlen)
>         ),
>  
>         TP_fast_assign(
>                 __entry->dr = dr;
>                 __entry->xid = be32_to_cpu(*(__be32 *)(dr->args +
>                                                        (dr-
> >xprt_hlen>>2)));
> -               __assign_str(addr, dr->xprt->xpt_remotebuf);
> +               memcpy(__get_dynamic_array(addr), &dr->addr, dr-
> >addrlen);
>         ),
>  
> -       TP_printk("addr=%s dr=%p xid=0x%08x", __get_str(addr),
> __entry->dr,
> -               __entry->xid)
> +       TP_printk("addr=%pISpc dr=%p xid=0x%08x",
> +               (struct sockaddr *)__get_dynamic_array(addr),
> +               __entry->dr, __entry->xid)
>  );
> 

Have you tested this? I found myself hitting the warning

"event %s has unsafe dereference of argument %d"

in test_event_printk() when I tried to use something similar for the
NFS code.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com