linux-hardening - Re: [PATCH] ceph: Annotate struct ceph_monmap with __counted

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Date:   Fri, 15 Sep 2023 14:51:20 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Kees Cook <keescook@...omium.org>,
        Ilya Dryomov <idryomov@...il.com>
Cc:     Xiubo Li <xiubli@...hat.com>, Jeff Layton <jlayton@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, ceph-devel@...r.kernel.org,
        netdev@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ceph: Annotate struct ceph_monmap with __counted_by



On 9/15/23 14:15, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct ceph_monmap.
> Additionally, since the element count member must be set before accessing
> the annotated flexible array member, move its initialization earlier.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Ilya Dryomov <idryomov@...il.com>
> Cc: Xiubo Li <xiubli@...hat.com>
> Cc: Jeff Layton <jlayton@...nel.org>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: ceph-devel@...r.kernel.org
> Cc: netdev@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks
-- 
Gustavo

> ---
>   include/linux/ceph/mon_client.h | 2 +-
>   net/ceph/mon_client.c           | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/ceph/mon_client.h b/include/linux/ceph/mon_client.h
> index b658961156a0..7a9a40163c0f 100644
> --- a/include/linux/ceph/mon_client.h
> +++ b/include/linux/ceph/mon_client.h
> @@ -19,7 +19,7 @@ struct ceph_monmap {
>   	struct ceph_fsid fsid;
>   	u32 epoch;
>   	u32 num_mon;
> -	struct ceph_entity_inst mon_inst[];
> +	struct ceph_entity_inst mon_inst[] __counted_by(num_mon);
>   };
>   
>   struct ceph_mon_client;
> diff --git a/net/ceph/mon_client.c b/net/ceph/mon_client.c
> index faabad6603db..f263f7e91a21 100644
> --- a/net/ceph/mon_client.c
> +++ b/net/ceph/mon_client.c
> @@ -1136,6 +1136,7 @@ static int build_initial_monmap(struct ceph_mon_client *monc)
>   			       GFP_KERNEL);
>   	if (!monc->monmap)
>   		return -ENOMEM;
> +	monc->monmap->num_mon = num_mon;
>   
>   	for (i = 0; i < num_mon; i++) {
>   		struct ceph_entity_inst *inst = &monc->monmap->mon_inst[i];
> @@ -1147,7 +1148,6 @@ static int build_initial_monmap(struct ceph_mon_client *monc)
>   		inst->name.type = CEPH_ENTITY_TYPE_MON;
>   		inst->name.num = cpu_to_le64(i);
>   	}
> -	monc->monmap->num_mon = num_mon;
>   	return 0;
>   }
>