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

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Date:   Mon, 18 Sep 2023 10:25:33 +0800
From:   Xiubo Li <xiubli@...hat.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Kees Cook <keescook@...omium.org>,
        Ilya Dryomov <idryomov@...il.com>
Cc:     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 9/18/23 10:04, Gustavo A. R. Silva wrote:
>
>
> On 9/17/23 18:25, Xiubo Li wrote:
>>
>> On 9/16/23 04:15, 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>
>>> ---
>>>   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;
>>
>> BTW, is this change related ?
>
> Yes, it is, and it's described in the changelog text.
>
> `num_mon` must be updated before the first access to flex-array 
> `mon_inst`.
> Otherwise the compiler cannot properly instrument the code to catch any
> out-of-bounds access to `mon_inst`.
>
Okay, got it.

Thanks

- Xiubo


> -- 
> Gustavo
>
>>
>>>       return 0;
>>>   }
>>
>> Else LGTM.
>>
>> Reviewed-by: Xiubo Li <xiubli@...hat.com>
>>
>> Thanks!
>>
>> - Xiubo
>>
>>
>