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SubjectRe: NFS mounts failing when keytab present on client
On Tue, 27 Mar 2018, Eric Biggers wrote:

> Hi Michael,
>
> On Tue, Mar 27, 2018 at 11:06:14PM +0100, Michael Young wrote:
> > NFS mounts stopped working on one of my computers after a kernel update from
> > 4.15.3 to 4.15.4. I traced the problem to the commit
> > [46e8d06e423c4f35eac7a8b677b713b3ec9b0684] crypto: hash - prevent using
> > keyed hashes without setting key
> > and a later kernel with this patch reverted works normally.
> >
> > The problem seems to be related to kerberos as the mount fails when the
> > keytab is present, but works if I rename the keytab file. This is true even
> > though the mount is with sec=sys . The mount should also work with sec=krb5
> > but that also fails in the same way. When the mount fails there are errors
> > in dmesg like
> > [ 1232.522816] gss_marshal: gss_get_mic FAILED (851968)
> > [ 1232.522819] RPC: couldn't encode RPC header, exit EIO
> > [ 1232.522856] gss_marshal: gss_get_mic FAILED (851968)
> > [ 1232.522857] RPC: couldn't encode RPC header, exit EIO
> > [ 1232.522863] NFS: nfs4_discover_server_trunking unhandled error -5.
> > Exiting with error EIO
> > [ 1232.525039] gss_marshal: gss_get_mic FAILED (851968)
> > [ 1232.525042] RPC: couldn't encode RPC header, exit EIO
> >
> > Michael Young
>
> Thanks for the bug report. I think the error is coming from
> net/sunrpc/auth_gss/gss_krb5_crypto.c. There are two potential problems I see.
> The first one, which is definitely a bug, is that make_checksum_hmac_md5()
> allocates an HMAC transform and request, then does these crypto API calls:
>
> crypto_ahash_init()
> crypto_ahash_setkey()
> crypto_ahash_digest()
>
> This is wrong because it makes no sense to init() the HMAC request before the
> key has been set, and doubly so when it's calling digest() which is shorthand
> for init() + update() + final(). So I think it just needs to be removed. You
> can test the following patch:
>
> diff --git a/net/sunrpc/auth_gss/gss_krb5_crypto.c b/net/sunrpc/auth_gss/gss_krb5_crypto.c
> index 12649c9fedab..8654494b4d0a 100644
> --- a/net/sunrpc/auth_gss/gss_krb5_crypto.c
> +++ b/net/sunrpc/auth_gss/gss_krb5_crypto.c
> @@ -237,9 +237,6 @@ make_checksum_hmac_md5(struct krb5_ctx *kctx, char *header, int hdrlen,
>
> ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP, NULL, NULL);
>
> - err = crypto_ahash_init(req);
> - if (err)
> - goto out;
> err = crypto_ahash_setkey(hmac_md5, cksumkey, kctx->gk5e->keylength);
> if (err)
> goto out;
>
> If that's not it, it's also possible that the error is coming from the
> crypto_ahash_init() in make_checksum(). That can only happen if 'cksumkey' is
> NULL and the hash algorithm is keyed, which implies a logical error as it
> doesn't make sense to use a keyed hash algorithm without the key. The callers
> do check kctx->gk5e->keyed_cksum which I'd hope would prevent this, though
> perhaps kctx->cksum can be NULL.
>
> Eric

The patch fixes the problem.

Michael Young

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