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Wed, 24 Jul 2019 12:12:45 -0700 (PDT) Received: by localhost.localdomain (Postfix, from userid 1000) id 574C3C1BD5; Wed, 24 Jul 2019 16:12:43 -0300 (-03) Date: Wed, 24 Jul 2019 16:12:43 -0300 From: Marcelo Ricardo Leitner To: Neil Horman Cc: Xin Long , network dev , linux-sctp@vger.kernel.org, davem Subject: Re: [PATCH net-next 1/4] sctp: check addr_size with sa_family_t size in __sctp_setsockopt_connectx Message-ID: <20190724191243.GA4063@localhost.localdomain> References: <20190723152449.GB8419@localhost.localdomain> <20190724112235.GA7212@hmswarspite.think-freely.org> <20190724123650.GD6204@localhost.localdomain> <20190724124907.GA8640@localhost.localdomain> <20190724184456.GC7212@hmswarspite.think-freely.org> <20190724190543.GH6204@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190724190543.GH6204@localhost.localdomain> User-Agent: Mutt/1.12.0 (2019-05-25) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Jul 24, 2019 at 04:05:43PM -0300, Marcelo Ricardo Leitner wrote: > On Wed, Jul 24, 2019 at 02:44:56PM -0400, Neil Horman wrote: > > On Wed, Jul 24, 2019 at 09:49:07AM -0300, Marcelo Ricardo Leitner wrote: > > > On Wed, Jul 24, 2019 at 09:36:50AM -0300, Marcelo Ricardo Leitner wrote: > > > > On Wed, Jul 24, 2019 at 07:22:35AM -0400, Neil Horman wrote: > > > > > On Wed, Jul 24, 2019 at 03:21:12PM +0800, Xin Long wrote: > > > > > > On Tue, Jul 23, 2019 at 11:25 PM Neil Horman wrote: > > > > > > > > > > > > > > On Tue, Jul 23, 2019 at 01:37:57AM +0800, Xin Long wrote: > > > > > > > > Now __sctp_connect() is called by __sctp_setsockopt_connectx() and > > > > > > > > sctp_inet_connect(), the latter has done addr_size check with size > > > > > > > > of sa_family_t. > > > > > > > > > > > > > > > > In the next patch to clean up __sctp_connect(), we will remove > > > > > > > > addr_size check with size of sa_family_t from __sctp_connect() > > > > > > > > for the 1st address. > > > > > > > > > > > > > > > > So before doing that, __sctp_setsockopt_connectx() should do > > > > > > > > this check first, as sctp_inet_connect() does. > > > > > > > > > > > > > > > > Signed-off-by: Xin Long > > > > > > > > --- > > > > > > > > net/sctp/socket.c | 2 +- > > > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > > > > > diff --git a/net/sctp/socket.c b/net/sctp/socket.c > > > > > > > > index aa80cda..5f92e4a 100644 > > > > > > > > --- a/net/sctp/socket.c > > > > > > > > +++ b/net/sctp/socket.c > > > > > > > > @@ -1311,7 +1311,7 @@ static int __sctp_setsockopt_connectx(struct sock *sk, > > > > > > > > pr_debug("%s: sk:%p addrs:%p addrs_size:%d\n", > > > > > > > > __func__, sk, addrs, addrs_size); > > > > > > > > > > > > > > > > - if (unlikely(addrs_size <= 0)) > > > > > > > > + if (unlikely(addrs_size < sizeof(sa_family_t))) > > > > > > > I don't think this is what you want to check for here. sa_family_t is > > > > > > > an unsigned short, and addrs_size is the number of bytes in the addrs > > > > > > > array. The addrs array should be at least the size of one struct > > > > > > > sockaddr (16 bytes iirc), and, if larger, should be a multiple of > > > > > > > sizeof(struct sockaddr) > > > > > > sizeof(struct sockaddr) is not the right value to check either. > > > > > > > > > > > > The proper check will be done later in __sctp_connect(): > > > > > > > > > > > > af = sctp_get_af_specific(daddr->sa.sa_family); > > > > > > if (!af || af->sockaddr_len > addrs_size) > > > > > > return -EINVAL; > > > > > > > > > > > > So the check 'addrs_size < sizeof(sa_family_t)' in this patch is > > > > > > just to make sure daddr->sa.sa_family is accessible. the same > > > > > > check is also done in sctp_inet_connect(). > > > > > > > > > > > That doesn't make much sense, if the proper check is done in __sctp_connect with > > > > > the size of the families sockaddr_len, then we don't need this check at all, we > > > > > can just let memdup_user take the fault on copy_to_user and return -EFAULT. If > > > > > we get that from memdup_user, we know its not accessible, and can bail out. > > > > > > > > > > About the only thing we need to check for here is that addr_len isn't some > > > > > absurdly high value (i.e. a negative value), so that we avoid trying to kmalloc > > > > > upwards of 2G in memdup_user. Your change does that just fine, but its no > > > > > better or worse than checking for <=0 > > > > > > > > One can argue that such check against absurdly high values is random > > > > and not effective, as 2G can be somewhat reasonable on 8GB systems but > > > > certainly isn't on 512MB ones. On that, kmemdup_user() will also fail > > > > gracefully as it uses GFP_USER and __GFP_NOWARN. > > > > > > > > The original check is more for protecting for sane usage of the > > > > variable, which is an int, and a negative value is questionable. We > > > > could cast, yes, but.. was that really the intent of the application? > > > > Probably not. > > > > > > Though that said, I'm okay with the new check here: a quick sanity > > > check that can avoid expensive calls to kmalloc(), while more refined > > > check is done later on. > > > > > I agree a sanity check makes sense, just to avoid allocating a huge value > > (even 2G is absurd on many systems), however, I'm not super comfortable with > > checking for the value being less than 16 (sizeof(sa_family_t)). The zero check > > 16 bits you mean then, per > include/uapi/linux/socket.h > typedef unsigned short __kernel_sa_family_t; > include/linux/socket.h > typedef __kernel_sa_family_t sa_family_t; > > > is fairly obvious given the signed nature of the lengh field, this check makes > > me wonder what exactly we are checking for. > > A minimum viable buffer without doing more extensive tests. Beyond > sa_family, we need to parse sa_family and then that's left for later. > Perhaps a comment helps, something like > /* Check if we have at least the family type in there */ > ? Hm, then this could be - if (unlikely(addrs_size <= 0)) + if (unlikely(addrs_size < sizeof(struct sockaddr_in))) (ipv4) As it can't be smaller than that, always. > > Marcelo > > > > > Neil > > > > > > > > > > > > > > > > Neil > > > > > > > > > > > > > > > > > > > Neil > > > > > > > > > > > > > > > return -EINVAL; > > > > > > > > > > > > > > > > kaddrs = memdup_user(addrs, addrs_size); > > > > > > > > -- > > > > > > > > 2.1.0 > > > > > > > > > > > > > > > > > > > > > > > > > >