From mboxrd@z Thu Jan 1 00:00:00 1970 From: Willy Tarreau Subject: Re: [PATCH] Change judgment len position Date: Wed, 24 Oct 2018 18:32:30 +0200 Message-ID: <20181024163230.GA25382@1wt.eu> References: <20181024154729.5312-1-wanghaifine@gmail.com> <20181024155739.GA25314@1wt.eu> <60f08664db5751949ddfb34666bfda77f99682f1.camel@perches.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Wang Hai , edumazet@google.com, davem@davemloft.net, kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Joe Perches Return-path: Content-Disposition: inline In-Reply-To: <60f08664db5751949ddfb34666bfda77f99682f1.camel@perches.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, Oct 24, 2018 at 09:23:19AM -0700, Joe Perches wrote: > On Wed, 2018-10-24 at 17:57 +0200, Willy Tarreau wrote: > > On Wed, Oct 24, 2018 at 11:47:29PM +0800, Wang Hai wrote: > > > To determine whether len is less than zero, it should be put before > > > the function min_t, because the return value of min_t is not likely > > > to be less than zero. > > > > Huh? First, the <0 test is made on "len", not "min_t", so it still > > is signed. Second, you're in fact completely removing the test here, > > look : > > > > > struct net *net = sock_net(sk); > > > int val, len; > > > > > > + len = min_t(unsigned int, len, sizeof(int)); > > > + > > > > len is used uninitialized here, so the result is undefined. > > > > > if (get_user(len, optlen)) > > > return -EFAULT; > > > > Then it gets overridden by get_user() > > > > > - len = min_t(unsigned int, len, sizeof(int)); > > > - > > > > Then its positive values are not bounded anymore since you moved the test. > > Not quite. > > Problem here is negative values are tested as > large positive values and limited to 4 > > ie: > ien len = -1, > len = min_t(unsigned int, len, sizeof(int)); > > len is now 4 > > > > if (len < 0) > > > return -EINVAL; > > So this test len < 0 could be moved up above min_t It could indeed, or we could also have min_t() done on an int instead of an unsigned int and this would avoid the need to shuffle the code around and open a huge hole like this one. Willy