From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jason A. Donenfeld" Date: Mon, 27 Jul 2020 16:16:32 +0000 Subject: Re: [PATCH 12/26] netfilter: switch nf_setsockopt to sockptr_t Message-Id: List-Id: References: <20200723060908.50081-1-hch@lst.de> <20200723060908.50081-13-hch@lst.de> <20200727150310.GA1632472@zx2c4.com> <20200727150601.GA3447@lst.de> In-Reply-To: <20200727150601.GA3447@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Christoph Hellwig Cc: "David S. Miller" , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Alexey Kuznetsov , Hideaki YOSHIFUJI , Eric Dumazet , Linux Crypto Mailing List , LKML , Netdev , bpf@vger.kernel.org, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, linux-sctp@vger.kernel.org, linux-hams@vger.kernel.org, linux-bluetooth@vger.kernel.org, bridge@lists.linux-foundation.org, linux-can@vger.kernel.org, dccp@vger.kernel.org, linux-decnet-user@lists.sourceforge.net, linux-wpan@vger.kernel.org, linux-s390@vger.kernel.org, mptcp@lists.01.org, lvs-devel@vger.kernel.org, rds-devel@oss.oracle.com, linux-afs@lists.infradead.org, tipc-discussion@lists.sourceforge.net, linux-x25@vger.kernel.org, Kernel Hardening On Mon, Jul 27, 2020 at 5:06 PM Christoph Hellwig wrote: > > On Mon, Jul 27, 2020 at 05:03:10PM +0200, Jason A. Donenfeld wrote: > > Hi Christoph, > > > > On Thu, Jul 23, 2020 at 08:08:54AM +0200, Christoph Hellwig wrote: > > > diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c > > > index da933f99b5d517..42befbf12846c0 100644 > > > --- a/net/ipv4/ip_sockglue.c > > > +++ b/net/ipv4/ip_sockglue.c > > > @@ -1422,7 +1422,8 @@ int ip_setsockopt(struct sock *sk, int level, > > > optname != IP_IPSEC_POLICY && > > > optname != IP_XFRM_POLICY && > > > !ip_mroute_opt(optname)) > > > - err = nf_setsockopt(sk, PF_INET, optname, optval, optlen); > > > + err = nf_setsockopt(sk, PF_INET, optname, USER_SOCKPTR(optval), > > > + optlen); > > > #endif > > > return err; > > > } > > > diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c > > > index 4697d09c98dc3e..f2a9680303d8c0 100644 > > > --- a/net/ipv4/netfilter/ip_tables.c > > > +++ b/net/ipv4/netfilter/ip_tables.c > > > @@ -1102,7 +1102,7 @@ __do_replace(struct net *net, const char *name, unsigned int valid_hooks, > > > } > > > > > > static int > > > -do_replace(struct net *net, const void __user *user, unsigned int len) > > > +do_replace(struct net *net, sockptr_t arg, unsigned int len) > > > { > > > int ret; > > > struct ipt_replace tmp; > > > @@ -1110,7 +1110,7 @@ do_replace(struct net *net, const void __user *user, unsigned int len) > > > void *loc_cpu_entry; > > > struct ipt_entry *iter; > > > > > > - if (copy_from_user(&tmp, user, sizeof(tmp)) != 0) > > > + if (copy_from_sockptr(&tmp, arg, sizeof(tmp)) != 0) > > > return -EFAULT; > > > > > > /* overflow check */ > > > @@ -1126,8 +1126,8 @@ do_replace(struct net *net, const void __user *user, unsigned int len) > > > return -ENOMEM; > > > > > > loc_cpu_entry = newinfo->entries; > > > - if (copy_from_user(loc_cpu_entry, user + sizeof(tmp), > > > - tmp.size) != 0) { > > > + sockptr_advance(arg, sizeof(tmp)); > > > + if (copy_from_sockptr(loc_cpu_entry, arg, tmp.size) != 0) { > > > ret = -EFAULT; > > > goto free_newinfo; > > > } > > > > Something along this path seems to have broken with this patch. An > > invocation of `iptables -A INPUT -m length --length 1360 -j DROP` now > > fails, with > > > > nf_setsockopt->do_replace->translate_table->check_entry_size_and_hooks: > > (unsigned char *)e + e->next_offset > limit => TRUE > > > > resulting in the whole call chain returning -EINVAL. It bisects back to > > this commit. This is on net-next. > > This is another use o sockptr_advance that Ido already found a problem > in. I'm looking into this at the moment.. I haven't seen Ido's patch, but it seems clear the issue is that you want to call `sockptr_advance(&arg, sizeof(tmp))`, and adjust sockptr_advance to take a pointer. Slight concern about the whole concept: Things are defined as typedef union { void *kernel; void __user *user; } sockptr_t; static inline bool sockptr_is_kernel(sockptr_t sockptr) { return (unsigned long)sockptr.kernel >= TASK_SIZE; } So what happens if we have some code like: sockptr_t sp; init_user_sockptr(&sp, user_controlled_struct.extra_user_ptr); sockptr_advance(&sp, user_controlled_struct.some_big_offset); copy_to_sockptr(&sp, user_controlled_struct.a_few_bytes, sizeof(user_controlled_struct.a_few_bytes)); With the user controlling some_big_offset, he can convert the user sockptr into a kernel sockptr, causing the subsequent copy_to_sockptr to be a vanilla memcpy, after which a security disaster ensues. Maybe sockptr_advance should have some safety checks and sometimes return -EFAULT? Or you should always use the implementation where being a kernel address is an explicit bit of sockptr_t, rather than being implicit?