Re: [PATCH] ceph: fix decoding of client session messages flags

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2022-05-23 at 17:09 +0100, Luís Henriques wrote:
> The cephfs kernel client started to show  the message:
> 
>  ceph: mds0 session blocklisted
> 
> when mounting a filesystem.  This is due to the fact that the session
> messages are being incorrectly decoded: the skip needs to take into
> account the 'len'.
> 
> While there, fixed some whitespaces too.
> 
> Fixes: e1c9788cb397 ("ceph: don't rely on error_string to validate blocklisted session.")
> Signed-off-by: Luís Henriques <lhenriques@suse.de>
> ---
>  fs/ceph/mds_client.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> index 00c3de177dd6..1bd3e1bb0fdf 100644
> --- a/fs/ceph/mds_client.c
> +++ b/fs/ceph/mds_client.c
> @@ -3375,13 +3375,17 @@ static void handle_session(struct ceph_mds_session *session,
>  	}
>  
>  	if (msg_version >= 5) {
> -		u32 flags;
> -		/* version >= 4, struct_v, struct_cv, len, metric_spec */
> -	        ceph_decode_skip_n(&p, end, 2 + sizeof(u32) * 2, bad);
> +		u32 flags, len;
> +
> +		/* version >= 4 */
> +		ceph_decode_skip_16(&p, end, bad); /* struct_v, struct_cv */
> +		ceph_decode_32_safe(&p, end, len, bad); /* len */
> +		ceph_decode_skip_n(&p, end, len, bad); /* metric_spec */
> +
>  		/* version >= 5, flags   */
> -                ceph_decode_32_safe(&p, end, flags, bad);
> +		ceph_decode_32_safe(&p, end, flags, bad);
>  		if (flags & CEPH_SESSION_BLOCKLISTED) {
> -		        pr_warn("mds%d session blocklisted\n", session->s_mds);
> +			pr_warn("mds%d session blocklisted\n", session->s_mds);
>  			blocklisted = true;
>  		}
>  	}

Good catch! Should we send this to stable too?

Reviewed-by: Jeff Layton <jlayton@kernel.org>