ACK: [PATCH 1/1] net: Set sk_prot_creator when cloning sockets to the right proto

[Evgenii Shatokhin]

Hi,

On 18.12.2018 20:00, Kleber Souza wrote:
> On 12/6/18 10:59 PM, Tyler Hicks wrote:
>> From: Christoph Paasch <cpaasch at apple.com>
>>
>> sk->sk_prot and sk->sk_prot_creator can differ when the app uses
>> IPV6_ADDRFORM (transforming an IPv6-socket to an IPv4-one).
>> Which is why sk_prot_creator is there to make sure that sk_prot_free()
>> does the kmem_cache_free() on the right kmem_cache slab.
>>
>> Now, if such a socket gets transformed back to a listening socket (using
>> connect() with AF_UNSPEC) we will allocate an IPv4 tcp_sock through
>> sk_clone_lock() when a new connection comes in. But sk_prot_creator will
>> still point to the IPv6 kmem_cache (as everything got copied in
>> sk_clone_lock()). When freeing, we will thus put this
>> memory back into the IPv6 kmem_cache although it was allocated in the
>> IPv4 cache. I have seen memory corruption happening because of this.
>>
>> With slub-debugging and MEMCG_KMEM enabled this gives the warning
>> 	"cache_from_obj: Wrong slab cache. TCPv6 but object is from TCP"
>>
>> A C-program to trigger this:
>>
>> void main(void)
>> {
>>          int fd = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);
>>          int new_fd, newest_fd, client_fd;
>>          struct sockaddr_in6 bind_addr;
>>          struct sockaddr_in bind_addr4, client_addr1, client_addr2;
>>          struct sockaddr unsp;
>>          int val;
>>
>>          memset(&bind_addr, 0, sizeof(bind_addr));
>>          bind_addr.sin6_family = AF_INET6;
>>          bind_addr.sin6_port = ntohs(42424);
>>
>>          memset(&client_addr1, 0, sizeof(client_addr1));
>>          client_addr1.sin_family = AF_INET;
>>          client_addr1.sin_port = ntohs(42424);
>>          client_addr1.sin_addr.s_addr = inet_addr("127.0.0.1");
>>
>>          memset(&client_addr2, 0, sizeof(client_addr2));
>>          client_addr2.sin_family = AF_INET;
>>          client_addr2.sin_port = ntohs(42421);
>>          client_addr2.sin_addr.s_addr = inet_addr("127.0.0.1");
>>
>>          memset(&unsp, 0, sizeof(unsp));
>>          unsp.sa_family = AF_UNSPEC;
>>
>>          bind(fd, (struct sockaddr *)&bind_addr, sizeof(bind_addr));
>>
>>          listen(fd, 5);
>>
>>          client_fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
>>          connect(client_fd, (struct sockaddr *)&client_addr1, sizeof(client_addr1));
>>          new_fd = accept(fd, NULL, NULL);
>>          close(fd);
>>
>>          val = AF_INET;
>>          setsockopt(new_fd, SOL_IPV6, IPV6_ADDRFORM, &val, sizeof(val));
>>
>>          connect(new_fd, &unsp, sizeof(unsp));
>>
>>          memset(&bind_addr4, 0, sizeof(bind_addr4));
>>          bind_addr4.sin_family = AF_INET;
>>          bind_addr4.sin_port = ntohs(42421);
>>          bind(new_fd, (struct sockaddr *)&bind_addr4, sizeof(bind_addr4));
>>
>>          listen(new_fd, 5);
>>
>>          client_fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
>>          connect(client_fd, (struct sockaddr *)&client_addr2, sizeof(client_addr2));
>>
>>          newest_fd = accept(new_fd, NULL, NULL);
>>          close(new_fd);
>>
>>          close(client_fd);
>>          close(new_fd);
>> }
>>
>> As far as I can see, this bug has been there since the beginning of the
>> git-days.
>>
>> Signed-off-by: Christoph Paasch <cpaasch at apple.com>
>> Reviewed-by: Eric Dumazet <edumazet at google.com>
>> Signed-off-by: David S. Miller <davem at davemloft.net>
>>
>> CVE-2018-9568
>>
>> (cherry picked from commit 9d538fa60bad4f7b23193c89e843797a1cf71ef3)
>> Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
> Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>

If you plan to prepare a livepatch for Xenial with this fix, please 
consider this issue: https://github.com/dynup/kpatch/issues/931. It 
might affect livepatches for at least the kernel 4.4.0-x from Xenial as 
well.

I haven't checked that kernel yet but if sk_update_clone() is inlined 
into sk_clone_lock() there too, the static key condition used in 
sk_update_clone() could be broken in the patched code and always 
evaluate to false:

	if (mem_cgroup_sockets_enabled && sk->sk_cgrp)
		sock_update_memcg(newsk);

include/net/sock.h:
#define mem_cgroup_sockets_enabled 
static_key_false(&memcg_socket_limit_enabled)

This could result in hard-to-debug kernel crashes due to incorrect 
socket accounting in memcg when livepatch is used.

I have mentioned the workaround in that issue at Github: just change 
that condition in sk_update_clone() too in the livepatch to check the 
static key explicitly, smth. like this:

--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1470,7 +1470,7 @@ EXPORT_SYMBOL(sk_release_kernel);

  static void sk_update_clone(const struct sock *sk, struct sock *newsk)
  {
-	if (mem_cgroup_sockets_enabled && sk->sk_cgrp)
+	if (static_key_enabled(&memcg_socket_limit_enabled) && sk->sk_cgrp)
  		sock_update_memcg(newsk);
  }

It seems, Bionic kernels 4.15.0-x are not affected, but I am not 100% sure.

Regards,
Evgenii

>> ---
>>   net/core/sock.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/net/core/sock.c b/net/core/sock.c
>> index a2702d5d03bf..871e98eb8dd1 100644
>> --- a/net/core/sock.c
>> +++ b/net/core/sock.c
>> @@ -1511,6 +1511,8 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
>>   
>>   		sock_copy(newsk, sk);
>>   
>> +		newsk->sk_prot_creator = sk->sk_prot;
>> +
>>   		/* SANITY */
>>   		get_net(sock_net(newsk));
>>   		sk_node_init(&newsk->sk_node);
> 
> 
>