From fd41868a3c32b9e3f5ca604b70672de1fd695623 Mon Sep 17 00:00:00 2001 From: Alexey Dobriyan Date: Fri, 2 Dec 2016 04:11:34 +0300 Subject: [PATCH] netns: publish net_generic correctly Publishing net_generic pointer is done with silly mistake: new array is published BEFORE setting freshly acquired pernet subsystem pointer. memcpy rcu_assign_pointer kfree_rcu ng->ptr[id - 1] = data; This bug was introduced with commit 2d692957ee98cd40d80fa566bc217415a3b5acf6 ("[NETNS]: The generic per-net pointers.") in the glorious days of chopping networking stack into containers proper 8.5 years ago (whee...) How it didn't trigger for so long? Well, you need quite specific set of conditions: *) race window opens once per pernet subsystem addition (read: modprobe or boot) *) not every pernet subsystem is eligible (need ->id and ->size) *) not every pernet subsystem is vulnerable (need incorrect or absense of ordering of register_pernet_sybsys() and actually using net_generic()) *) to hide the bug even more, default is to preallocate 13 pointers which is actually quite a lot. You need IPv6, netfilter, bridging etc together loaded to trigger reallocation in the first place. Trimmed down config are OK. Signed-off-by: Alexey Dobriyan Signed-off-by: David S. Miller --- net/core/net_namespace.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c index a38feac547d77..707b3c25cb80b 100644 --- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -64,9 +64,10 @@ static int net_assign_generic(struct net *net, unsigned int id, void *data) old_ng = rcu_dereference_protected(net->gen, lockdep_is_held(&net_mutex)); - ng = old_ng; - if (old_ng->len >= id) - goto assign; + if (old_ng->len >= id) { + old_ng->ptr[id - 1] = data; + return 0; + } ng = net_alloc_generic(); if (ng == NULL) @@ -84,11 +85,10 @@ static int net_assign_generic(struct net *net, unsigned int id, void *data) */ memcpy(&ng->ptr, &old_ng->ptr, old_ng->len * sizeof(void*)); + ng->ptr[id - 1] = data; rcu_assign_pointer(net->gen, ng); kfree_rcu(old_ng, rcu); -assign: - ng->ptr[id - 1] = data; return 0; } -- 2.39.5