On Tue, Apr 02, 2024 at 12:56:42PM +0200, Florian Westphal wrote:
> Ziyang Xuan <william.xuanziyang@xxxxxxxxxx> wrote:
> > nft_unregister_flowtable_type() within nf_flow_inet_module_exit() can
> > concurrent with __nft_flowtable_type_get() within nf_tables_newflowtable().
> > And thhere is not any protection when iterate over nf_tables_flowtables
> > list in __nft_flowtable_type_get(). Therefore, there is pertential
> > data-race of nf_tables_flowtables list entry.
> >
> > Use list_for_each_entry_rcu() with rcu_read_lock() to Iterate over
> > nf_tables_flowtables list in __nft_flowtable_type_get() to resolve it.
>
> I don't think this resolves the described race.
>
> > Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx>
> > ---
> > net/netfilter/nf_tables_api.c | 8 ++++++--
> > 1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
> > index fd86f2720c9e..fbf38e32f11d 100644
> > --- a/net/netfilter/nf_tables_api.c
> > +++ b/net/netfilter/nf_tables_api.c
> > @@ -8297,10 +8297,14 @@ static const struct nf_flowtable_type *__nft_flowtable_type_get(u8 family)
> > {
> > const struct nf_flowtable_type *type;
> >
> > - list_for_each_entry(type, &nf_tables_flowtables, list) {
> > - if (family == type->family)
> > + rcu_read_lock()
> > + list_for_each_entry_rcu(type, &nf_tables_flowtables, list) {
> > + if (family == type->family) {
> > + rcu_read_unlock();
> > return type;
>
> This means 'type' can be non-null while module is being unloaded,
> before refcount increment.
>
> You need acquire rcu_read_lock() in the caller, nft_flowtable_type_get,
> and release it after refcount on module owner failed or succeeded.
And these need to be rcu protected:
static LIST_HEAD(nf_tables_expressions);
static LIST_HEAD(nf_tables_objects);
static LIST_HEAD(nf_tables_flowtables);
for a complete fix for:
f102d66b335a ("netfilter: nf_tables: use dedicated mutex to guard transactions")
