Re: ls input/output error ("NFS: readdir(/) returns -5") on krb5 NFSv4 client using SHA2

Tyler W. Ross
2025-11-13T18:52:10Z

On Thursday, November 13th, 2025 at 11:12 AM, Chuck Lever <chuck.lever@oracle.com> wrote:

> Then I would start looking for differences between the Debian 13 and
> Fedora 43 kernel code base under net/sunrpc/ .
>
> Alternatively, "git bisect first, ask questions later" ... :-)

This is outside my day-to-day, so I don't have a workflow for this kind of
testing/debugging, but I'll see what I can do.

Thanks for the starting place.

> So I didn't find an indication of whether this was sec=krb5, sec=krb5i,
> or sec=krb5p. That might narrow down where the code changed.

I confirmed the issue with all 3 krb5 sec modes, in both the 6.12 kernel
that ships with Debian 13 and the 6.17 that currently ships with Debian
Sid/unstable. Similarly, I confirmed NFSv4.2, 4.1 and 4.0 are impacted.

> Also, the xdr_buf might have a page boundary positioned in the middle of
> an XDR data item. Knowing which data item is being decoded where the
> "overflow" occurs might be helpful (I think adding pr_info() call sites
> or trace_printk() will be adequate to gain some better observability).

No experience with kernel hacking, so I'm not confident I can locate
meaningful places to insert those.

I'll see where some snooping and a bisect gets me. Failing that, if
anyone has recommendations on where to add those calls, I'd appreciate
the guidance.

TWR