@@ -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;
}
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 dec827d174d7f76c457238800183ca864a639365 ("[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 <adobriyan@gmail.com> --- net/core/net_namespace.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)