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

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Date: Sun, 17 Sep 2023 20:04:28 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Xiubo Li <xiubli@...hat.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 9/17/23 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`.

--
Gustavo

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