Re: [PATCH] nfsd: Use MD5 library instead of crypto_shash

[Ard Biesheuvel]

On Sat, 11 Oct 2025 at 20:54, Eric Biggers <ebiggers@xxxxxxxxxx> wrote:
>
> Update NFSD's support for "legacy client tracking" (which uses MD5) to
> use the MD5 library instead of crypto_shash.  This has several benefits:
>
> - Simpler code.  Notably, much of the error-handling code is no longer
>   needed, since the library functions can't fail.
>
> - Improved performance due to reduced overhead.  A microbenchmark of
>   nfs4_make_rec_clidname() shows a speedup from 1455 cycles to 425.
>
> - The MD5 code can now safely be built as a loadable module when nfsd is
>   built as a loadable module.  (Previously, nfsd forced the MD5 code to
>   built-in, presumably to work around the unreliablity of the name-based
>   loading.)  Thus, select MD5 from the tristate option NFSD if
>   NFSD_LEGACY_CLIENT_TRACKING, instead of from the bool option NFSD_V4.
>
> To preserve the existing behavior of legacy client tracking support
> being disabled when the kernel is booted with "fips=1", make
> nfsd4_legacy_tracking_init() return an error if fips_enabled.  I don't
> know if this is truly needed, but it preserves the existing behavior.
>
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> ---
>  fs/nfsd/Kconfig       |  3 +-
>  fs/nfsd/nfs4recover.c | 82 ++++++++-----------------------------------
>  2 files changed, 16 insertions(+), 69 deletions(-)
>

Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>