This is a note to let you know that I've just added the patch titled

net: Fix double free and memory corruption in get_net_ns_by_id()

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: net-fix-double-free-and-memory-corruption-in-get_net_ns_by_id.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Sun Dec 31 11:20:35 CET 2017

From: "Eric W. Biederman" ebiederm@xmission.com Date: Tue, 19 Dec 2017 11:27:56 -0600 Subject: net: Fix double free and memory corruption in get_net_ns_by_id()

From: "Eric W. Biederman" ebiederm@xmission.com

[ Upstream commit 21b5944350052d2583e82dd59b19a9ba94a007f0 ]

(I can trivially verify that that idr_remove in cleanup_net happens after the network namespace count has dropped to zero --EWB)

Function get_net_ns_by_id() does not check for net::count after it has found a peer in netns_ids idr.

It may dereference a peer, after its count has already been finaly decremented. This leads to double free and memory corruption:

put_net(peer) rtnl_lock() atomic_dec_and_test(&peer->count) [count=0] ... __put_net(peer) get_net_ns_by_id(net, id) spin_lock(&cleanup_list_lock) list_add(&net->cleanup_list, &cleanup_list) spin_unlock(&cleanup_list_lock) queue_work() peer = idr_find(&net->netns_ids, id) | get_net(peer) [count=1] | ... | (use after final put) v ... cleanup_net() ... spin_lock(&cleanup_list_lock) ... list_replace_init(&cleanup_list, ..) ... spin_unlock(&cleanup_list_lock) ... ... ... ... put_net(peer) ... atomic_dec_and_test(&peer->count) [count=0] ... spin_lock(&cleanup_list_lock) ... list_add(&net->cleanup_list, &cleanup_list) ... spin_unlock(&cleanup_list_lock) ... queue_work() ... rtnl_unlock() rtnl_lock() ... for_each_net(tmp) { ... id = __peernet2id(tmp, peer) ... spin_lock_irq(&tmp->nsid_lock) ... idr_remove(&tmp->netns_ids, id) ... ... ... net_drop_ns() ... net_free(peer) ... } ... | v cleanup_net() ... (Second free of peer)

Also, put_net() on the right cpu may reorder with left's cpu list_replace_init(&cleanup_list, ..), and then cleanup_list will be corrupted.

Since cleanup_net() is executed in worker thread, while put_net(peer) can happen everywhere, there should be enough time for concurrent get_net_ns_by_id() to pick the peer up, and the race does not seem to be unlikely. The patch fixes the problem in standard way.

(Also, there is possible problem in peernet2id_alloc(), which requires check for net::count under nsid_lock and maybe_get_net(peer), but in current stable kernel it's used under rtnl_lock() and it has to be safe. Openswitch begun to use peernet2id_alloc(), and possibly it should be fixed too. While this is not in stable kernel yet, so I'll send a separate message to netdev@ later).

Cc: Nicolas Dichtel nicolas.dichtel@6wind.com Signed-off-by: Kirill Tkhai ktkhai@virtuozzo.com Fixes: 0c7aecd4bde4 "netns: add rtnl cmd to add and get peer netns ids" Reviewed-by: Andrey Ryabinin aryabinin@virtuozzo.com Reviewed-by: "Eric W. Biederman" ebiederm@xmission.com Signed-off-by: Eric W. Biederman ebiederm@xmission.com Reviewed-by: Eric Dumazet edumazet@google.com Acked-by: Nicolas Dichtel nicolas.dichtel@6wind.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/net_namespace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -261,7 +261,7 @@ struct net *get_net_ns_by_id(struct net spin_lock_irqsave(&net->nsid_lock, flags); peer = idr_find(&net->netns_ids, id); if (peer) - get_net(peer); + peer = maybe_get_net(peer); spin_unlock_irqrestore(&net->nsid_lock, flags); rcu_read_unlock();

Patches currently in stable-queue which might be from ebiederm@xmission.com are

queue-4.4/net-fix-double-free-and-memory-corruption-in-get_net_ns_by_id.patch