linux-hardening - Re: [PATCH 2/5][next] nfsd: avoid -Wflex-array-member-not-at-end warnings

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Message-ID: <Zw/KoQRfBl5Y9xyS@tissot.1015granger.net>
Date: Wed, 16 Oct 2024 10:16:01 -0400
From: Chuck Lever <chuck.lever@...cle.com>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Jeff Layton <jlayton@...nel.org>, Neil Brown <neilb@...e.de>,
        Olga Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>,
        Tom Talpey <tom@...pey.com>, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        Kees Cook <kees@...nel.org>
Subject: Re: [PATCH 2/5][next] nfsd: avoid -Wflex-array-member-not-at-end
 warnings

On Tue, Oct 15, 2024 at 06:29:31PM -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Address the following warnings by changing the type of the middle struct
> members in `struct nfsd_genl_rqstp`, which are currently causing trouble,
> from `struct sockaddr` to `struct sockaddr_legacy`. Note that the latter
> struct doesn't contain a flexible-array member.
> 
> fs/nfsd/nfsd.h:74:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> fs/nfsd/nfsd.h:75:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Also, update some related code, accordingly.
> 
> No binary differences are present after these changes.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>  fs/nfsd/nfsctl.c | 4 ++--
>  fs/nfsd/nfsd.h   | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index 3adbc05ebaac..884bfdc7a255 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -1599,9 +1599,9 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
>  			genl_rqstp.rq_stime = rqstp->rq_stime;
>  			genl_rqstp.rq_opcnt = 0;
>  			memcpy(&genl_rqstp.rq_daddr, svc_daddr(rqstp),
> -			       sizeof(struct sockaddr));
> +			       sizeof(struct sockaddr_legacy));
>  			memcpy(&genl_rqstp.rq_saddr, svc_addr(rqstp),
> -			       sizeof(struct sockaddr));
> +			       sizeof(struct sockaddr_legacy));
>  
>  #ifdef CONFIG_NFSD_V4
>  			if (rqstp->rq_vers == NFS4_VERSION &&
> diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
> index 004415651295..44be32510595 100644
> --- a/fs/nfsd/nfsd.h
> +++ b/fs/nfsd/nfsd.h
> @@ -71,8 +71,8 @@ struct readdir_cd {
>  #define NFSD_MAX_OPS_PER_COMPOUND	50
>  
>  struct nfsd_genl_rqstp {
> -	struct sockaddr		rq_daddr;
> -	struct sockaddr		rq_saddr;
> +	struct sockaddr_legacy	rq_daddr;
> +	struct sockaddr_legacy	rq_saddr;

I was hoping to find a struct definition that was simply a union of
sockaddr_in and sockaddr_in6, which we have in nfs-utils but I guess
not here in the kernel.

Can we use "struct sockaddr_storage" safely here? Then above,
replace the raw memcpy() with rpc_copy_addr() ?


>  	unsigned long		rq_flags;
>  	ktime_t			rq_stime;
>  	__be32			rq_xid;
> -- 
> 2.34.1
> 

-- 
Chuck Lever