From: ebiederm@xmission.com (Eric W. Biederman)
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Kees Cook <keescook@chromium.org>,
"David S. Miller" <davem@davemloft.net>,
Alexander Potapenko <glider@google.com>,
Kostya Serebryany <kcc@google.com>,
Andrey Konovalov <andreyknvl@google.com>,
Eric Dumazet <edumazet@google.com>,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
security@kernel.org
Subject: Re: [PATCH] net: recvmsg: Unconditionally zero struct sockaddr_storage
Date: Wed, 01 Nov 2017 07:48:36 -0500 [thread overview]
Message-ID: <871slikvvf.fsf@xmission.com> (raw)
In-Reply-To: <1509471094.3828.26.camel@edumazet-glaptop3.roam.corp.google.com> (Eric Dumazet's message of "Tue, 31 Oct 2017 10:31:34 -0700")
Eric Dumazet <eric.dumazet@gmail.com> writes:
> On Tue, 2017-10-31 at 09:14 -0700, Kees Cook wrote:
>> Some protocols do not correctly wipe the contents of the on-stack
>> struct sockaddr_storage sent down into recvmsg() (e.g. SCTP), and leak
>> kernel stack contents to userspace. This wipes it unconditionally before
>> per-protocol handlers run.
>>
>> Note that leaks like this are mitigated by building with
>> CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL=y
>>
>> Reported-by: Alexander Potapenko <glider@google.com>
>> Cc: "David S. Miller" <davem@davemloft.net>
>> Cc: netdev@vger.kernel.org
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>> ---
>> net/socket.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/net/socket.c b/net/socket.c
>> index c729625eb5d3..34183f4fbdf8 100644
>> --- a/net/socket.c
>> +++ b/net/socket.c
>> @@ -2188,6 +2188,7 @@ static int ___sys_recvmsg(struct socket *sock, struct user_msghdr __user *msg,
>> struct sockaddr __user *uaddr;
>> int __user *uaddr_len = COMPAT_NAMELEN(msg);
>>
>> + memset(&addr, 0, sizeof(addr));
>> msg_sys->msg_name = &addr;
>>
>
> This kind of patch comes every year.
>
> Standard answer is : We fix the buggy protocol, we do not make
> everything slower just because we are lazy.
>
> struct sockaddr is 128 bytes, but IPV4 only uses a fraction of it.
>
> Also memset() is using long word stores, so next 4-byte or 2-byte stores
> on same location hit a performance problem on x86.
>
> By adding all these defensive programming, we would give strong
> incentives to bypass the kernel for networking. That would be bad.
In this case it looks like the root cause is something in sctp
not filling in the ipv6 sin6_scope_id.
Which is not only a leak but a correctness bug.
I ran the reproducer test program and while none of the leak checkers
are telling me anything I have gotten as far as seeing that the returned
length is correct and sometimes nonsense.
Hmm.
At a quick look it looks like all that is necessary is to do this:
diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
index 51c488769590..6301913d0516 100644
--- a/net/sctp/ipv6.c
+++ b/net/sctp/ipv6.c
@@ -807,9 +807,10 @@ static void sctp_inet6_skb_msgname(struct sk_buff *skb, char *msgname,
addr->v6.sin6_flowinfo = 0;
addr->v6.sin6_port = sh->source;
addr->v6.sin6_addr = ipv6_hdr(skb)->saddr;
- if (ipv6_addr_type(&addr->v6.sin6_addr) & IPV6_ADDR_LINKLOCAL) {
+ if (ipv6_addr_type(&addr->v6.sin6_addr) & IPV6_ADDR_LINKLOCAL)
addr->v6.sin6_scope_id = sctp_v6_skb_iif(skb);
- }
+ else
+ addr->v6.sin6_scope_id = 0;
}
*addr_len = sctp_v6_addr_to_user(sctp_sk(skb->sk), addr);
Eric
next prev parent reply other threads:[~2017-11-01 12:48 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-31 16:14 [PATCH] net: recvmsg: Unconditionally zero struct sockaddr_storage Kees Cook
2017-10-31 17:31 ` Eric Dumazet
2017-11-01 12:48 ` Eric W. Biederman [this message]
2017-11-01 18:23 ` Kees Cook
2017-11-15 8:22 ` Alexander Potapenko
2017-11-16 4:17 ` [PATCH net] net/sctp: Always set scope_id in sctp_inet6_skb_msgname Eric W. Biederman
2017-11-16 14:00 ` David Miller
2017-11-15 2:13 ` [PATCH] net: recvmsg: Unconditionally zero struct sockaddr_storage Kees Cook
2017-11-15 18:37 ` Eric W. Biederman
2017-10-31 17:35 ` Ben Hutchings
2017-11-01 6:49 ` Willy Tarreau
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