Re: [PATCH v2] SUNRPC: Check if we need to recalculate slack estimates

[Chuck Lever <chuck.lever@oracle.com>]

On 11/20/25 7:12 AM, Scott Mayhew wrote:
> If the incoming GSS verifier is larger than what we previously recorded
> on the gss_auth, that would indicate the GSS cred/context used for that
> RPC is using a different enctype than the one used by the machine
> cred/context, and we should recalculate the slack variables accordingly.
> 
> Link: https://bugs.debian.org/1120598

Since there is a bug link, a Fixes: tag is recommended.


> Signed-off-by: Scott Mayhew <smayhew@redhat.com>
> ---
>  net/sunrpc/auth_gss/auth_gss.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
> index 5c095cb8cb20..bff5f10581a2 100644
> --- a/net/sunrpc/auth_gss/auth_gss.c
> +++ b/net/sunrpc/auth_gss/auth_gss.c
> @@ -1721,6 +1721,18 @@ gss_validate(struct rpc_task *task, struct xdr_stream *xdr)
>  	if (maj_stat)
>  		goto bad_mic;
>  
> +	/*
> +	 * Normally we only recalculate the slack variables once after
> +	 * creating a new gss_auth, but we should also do it if the incoming
> +	 * verifier has a larger size than what was previously recorded.
> +	 * When the incoming verifier is larger than expected, the
> +	 * GSS context is using a different enctype than the one used
> +	 * initially by the machine credential. Force a slack size update
> +	 * to maintain good payload alignment.
> +	 */
> +	if (cred->cr_auth->au_verfsize < (XDR_QUADLEN(len) + 2))
> +		__set_bit(RPCAUTH_AUTH_UPDATE_SLACK, &cred->cr_auth->au_flags);

set_bit() rather than __set_bit is a better choice for a lockless update
where multiple concurrent threads can have access to the flags field.


> +
>  	/* We leave it to unwrap to calculate au_rslack. For now we just
>  	 * calculate the length of the verifier: */
>  	if (test_bit(RPCAUTH_AUTH_UPDATE_SLACK, &cred->cr_auth->au_flags))

Thanks for pursuing this one, Scott.

Reviewed-by: Chuck Lever <chuck.lever@oracle.com>


-- 
Chuck Lever