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Message-ID: <5f405581-e7e2-4e77-8044-0496db85aa27@oracle.com>
Date: Sun, 12 Oct 2025 11:59:35 -0400
From: Chuck Lever <chuck.lever@...cle.com>
To: Eric Biggers <ebiggers@...nel.org>, Scott Mayhew <smayhew@...hat.com>,
Jeff Layton <jlayton@...nel.org>
Cc: NeilBrown <neil@...wn.name>, Olga Kornievskaia <okorniev@...hat.com>,
Dai Ngo <Dai.Ngo@...cle.com>, Tom Talpey <tom@...pey.com>,
linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-nfs@...r.kernel.org
Subject: Re: [PATCH] nfsd: Use MD5 library instead of crypto_shash
On 10/11/25 2:52 PM, Eric Biggers 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@...nel.org>
No objection, but let's cross our t's and dot our i's. Scott, when you
have recovered from bake-a-thon, can you have a look at this one?
Thanks!
> ---
> fs/nfsd/Kconfig | 3 +-
> fs/nfsd/nfs4recover.c | 82 ++++++++-----------------------------------
> 2 files changed, 16 insertions(+), 69 deletions(-)
>
> diff --git a/fs/nfsd/Kconfig b/fs/nfsd/Kconfig
> index e134dce45e350..380a4caa33a73 100644
> --- a/fs/nfsd/Kconfig
> +++ b/fs/nfsd/Kconfig
> @@ -3,10 +3,11 @@ config NFSD
> tristate "NFS server support"
> depends on INET
> depends on FILE_LOCKING
> depends on FSNOTIFY
> select CRC32
> + select CRYPTO_LIB_MD5 if NFSD_LEGACY_CLIENT_TRACKING
> select CRYPTO_LIB_SHA256 if NFSD_V4
> select LOCKD
> select SUNRPC
> select EXPORTFS
> select NFS_COMMON
> @@ -75,12 +76,10 @@ config NFSD_V3_ACL
> config NFSD_V4
> bool "NFS server support for NFS version 4"
> depends on NFSD && PROC_FS
> select FS_POSIX_ACL
> select RPCSEC_GSS_KRB5
> - select CRYPTO
> - select CRYPTO_MD5
> select GRACE_PERIOD
> select NFS_V4_2_SSC_HELPER if NFS_V4_2
> help
> This option enables support in your system's NFS server for
> version 4 of the NFS protocol (RFC 3530).
> diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
> index e2b9472e5c78c..dbc0aecef95e3 100644
> --- a/fs/nfsd/nfs4recover.c
> +++ b/fs/nfsd/nfs4recover.c
> @@ -30,13 +30,14 @@
> * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
> * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> *
> */
>
> -#include <crypto/hash.h>
> +#include <crypto/md5.h>
> #include <crypto/sha2.h>
> #include <linux/file.h>
> +#include <linux/fips.h>
> #include <linux/slab.h>
> #include <linux/namei.h>
> #include <linux/sched.h>
> #include <linux/fs.h>
> #include <linux/module.h>
> @@ -90,61 +91,22 @@ static void
> nfs4_reset_creds(const struct cred *original)
> {
> put_cred(revert_creds(original));
> }
>
> -static int
> +static void
> nfs4_make_rec_clidname(char dname[HEXDIR_LEN], const struct xdr_netobj *clname)
> {
> u8 digest[MD5_DIGEST_SIZE];
> - struct crypto_shash *tfm;
> - int status;
>
> dprintk("NFSD: nfs4_make_rec_clidname for %.*s\n",
> clname->len, clname->data);
> - tfm = crypto_alloc_shash("md5", 0, 0);
> - if (IS_ERR(tfm)) {
> - status = PTR_ERR(tfm);
> - goto out_no_tfm;
> - }
>
> - status = crypto_shash_tfm_digest(tfm, clname->data, clname->len,
> - digest);
> - if (status)
> - goto out;
> + md5(clname->data, clname->len, digest);
>
> static_assert(HEXDIR_LEN == 2 * MD5_DIGEST_SIZE + 1);
> sprintf(dname, "%*phN", MD5_DIGEST_SIZE, digest);
> -
> - status = 0;
> -out:
> - crypto_free_shash(tfm);
> -out_no_tfm:
> - return status;
> -}
> -
> -/*
> - * If we had an error generating the recdir name for the legacy tracker
> - * then warn the admin. If the error doesn't appear to be transient,
> - * then disable recovery tracking.
> - */
> -static void
> -legacy_recdir_name_error(struct nfs4_client *clp, int error)
> -{
> - printk(KERN_ERR "NFSD: unable to generate recoverydir "
> - "name (%d).\n", error);
> -
> - /*
> - * if the algorithm just doesn't exist, then disable the recovery
> - * tracker altogether. The crypto libs will generally return this if
> - * FIPS is enabled as well.
> - */
> - if (error == -ENOENT) {
> - printk(KERN_ERR "NFSD: disabling legacy clientid tracking. "
> - "Reboot recovery will not function correctly!\n");
> - nfsd4_client_tracking_exit(clp->net);
> - }
> }
>
> static void
> __nfsd4_create_reclaim_record_grace(struct nfs4_client *clp,
> const char *dname, int len, struct nfsd_net *nn)
> @@ -180,13 +142,11 @@ nfsd4_create_clid_dir(struct nfs4_client *clp)
> if (test_and_set_bit(NFSD4_CLIENT_STABLE, &clp->cl_flags))
> return;
> if (!nn->rec_file)
> return;
>
> - status = nfs4_make_rec_clidname(dname, &clp->cl_name);
> - if (status)
> - return legacy_recdir_name_error(clp, status);
> + nfs4_make_rec_clidname(dname, &clp->cl_name);
>
> status = nfs4_save_creds(&original_cred);
> if (status < 0)
> return;
>
> @@ -374,13 +334,11 @@ nfsd4_remove_clid_dir(struct nfs4_client *clp)
> struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
>
> if (!nn->rec_file || !test_bit(NFSD4_CLIENT_STABLE, &clp->cl_flags))
> return;
>
> - status = nfs4_make_rec_clidname(dname, &clp->cl_name);
> - if (status)
> - return legacy_recdir_name_error(clp, status);
> + nfs4_make_rec_clidname(dname, &clp->cl_name);
>
> status = mnt_want_write_file(nn->rec_file);
> if (status)
> goto out;
> clear_bit(NFSD4_CLIENT_STABLE, &clp->cl_flags);
> @@ -601,10 +559,15 @@ nfsd4_legacy_tracking_init(struct net *net)
> if (net != &init_net) {
> pr_warn("NFSD: attempt to initialize legacy client tracking in a container ignored.\n");
> return -EINVAL;
> }
>
> + if (fips_enabled) {
> + pr_warn("NFSD: legacy client tracking is disabled due to FIPS\n");
> + return -EINVAL;
> + }
> +
> status = nfs4_legacy_state_init(net);
> if (status)
> return status;
>
> status = nfsd4_load_reboot_recovery_data(net);
> @@ -657,25 +620,20 @@ nfs4_recoverydir(void)
> }
>
> static int
> nfsd4_check_legacy_client(struct nfs4_client *clp)
> {
> - int status;
> char dname[HEXDIR_LEN];
> struct nfs4_client_reclaim *crp;
> struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
> struct xdr_netobj name;
>
> /* did we already find that this client is stable? */
> if (test_bit(NFSD4_CLIENT_STABLE, &clp->cl_flags))
> return 0;
>
> - status = nfs4_make_rec_clidname(dname, &clp->cl_name);
> - if (status) {
> - legacy_recdir_name_error(clp, status);
> - return status;
> - }
> + nfs4_make_rec_clidname(dname, &clp->cl_name);
>
> /* look for it in the reclaim hashtable otherwise */
> name.data = kmemdup(dname, HEXDIR_LEN, GFP_KERNEL);
> if (!name.data) {
> dprintk("%s: failed to allocate memory for name.data!\n",
> @@ -1264,17 +1222,14 @@ nfsd4_cld_check(struct nfs4_client *clp)
> if (crp)
> goto found;
>
> #ifdef CONFIG_NFSD_LEGACY_CLIENT_TRACKING
> if (nn->cld_net->cn_has_legacy) {
> - int status;
> char dname[HEXDIR_LEN];
> struct xdr_netobj name;
>
> - status = nfs4_make_rec_clidname(dname, &clp->cl_name);
> - if (status)
> - return -ENOENT;
> + nfs4_make_rec_clidname(dname, &clp->cl_name);
>
> name.data = kmemdup(dname, HEXDIR_LEN, GFP_KERNEL);
> if (!name.data) {
> dprintk("%s: failed to allocate memory for name.data!\n",
> __func__);
> @@ -1315,15 +1270,12 @@ nfsd4_cld_check_v2(struct nfs4_client *clp)
>
> #ifdef CONFIG_NFSD_LEGACY_CLIENT_TRACKING
> if (cn->cn_has_legacy) {
> struct xdr_netobj name;
> char dname[HEXDIR_LEN];
> - int status;
>
> - status = nfs4_make_rec_clidname(dname, &clp->cl_name);
> - if (status)
> - return -ENOENT;
> + nfs4_make_rec_clidname(dname, &clp->cl_name);
>
> name.data = kmemdup(dname, HEXDIR_LEN, GFP_KERNEL);
> if (!name.data) {
> dprintk("%s: failed to allocate memory for name.data\n",
> __func__);
> @@ -1692,15 +1644,11 @@ nfsd4_cltrack_legacy_recdir(const struct xdr_netobj *name)
> /* just return nothing if output will be truncated */
> kfree(result);
> return NULL;
> }
>
> - copied = nfs4_make_rec_clidname(result + copied, name);
> - if (copied) {
> - kfree(result);
> - return NULL;
> - }
> + nfs4_make_rec_clidname(result + copied, name);
>
> return result;
> }
>
> static char *
>
> base-commit: 0739473694c4878513031006829f1030ec850bc2
--
Chuck Lever
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