Re: [PATCH net-next] net: dst: fix missing initialization of rt_uncached

[Leon Romanovsky <leon@kernel.org>]

On Wed, Apr 19, 2023 at 11:58:02AM +0300, Leon Romanovsky wrote:
> On Tue, Apr 18, 2023 at 06:54:26PM +0200, Maxime Bizon wrote:
> > xfrm_alloc_dst() followed by xfrm4_dst_destroy(), without a
> > xfrm4_fill_dst() call in between, causes the following BUG:
> > 
> >  BUG: spinlock bad magic on CPU#0, fbxhostapd/732
> >   lock: 0x890b7668, .magic: 890b7668, .owner: <none>/-1, .owner_cpu: 0
> >  CPU: 0 PID: 732 Comm: fbxhostapd Not tainted 6.3.0-rc6-next-20230414-00613-ge8de66369925-dirty #9
> >  Hardware name: Marvell Kirkwood (Flattened Device Tree)
> >   unwind_backtrace from show_stack+0x10/0x14
> >   show_stack from dump_stack_lvl+0x28/0x30
> >   dump_stack_lvl from do_raw_spin_lock+0x20/0x80
> >   do_raw_spin_lock from rt_del_uncached_list+0x30/0x64
> >   rt_del_uncached_list from xfrm4_dst_destroy+0x3c/0xbc
> >   xfrm4_dst_destroy from dst_destroy+0x5c/0xb0
> >   dst_destroy from rcu_process_callbacks+0xc4/0xec
> >   rcu_process_callbacks from __do_softirq+0xb4/0x22c
> >   __do_softirq from call_with_stack+0x1c/0x24
> >   call_with_stack from do_softirq+0x60/0x6c
> >   do_softirq from __local_bh_enable_ip+0xa0/0xcc
> > 
> > Patch "net: dst: Prevent false sharing vs. dst_entry:: __refcnt" moved
> > rt_uncached and rt_uncached_list fields from rtable struct to dst
> > struct, so they are more zeroed by memset_after(xdst, 0, u.dst) in
> > xfrm_alloc_dst().
> > 
> > Note that rt_uncached (list_head) was never properly initialized at
> > alloc time, but xfrm[46]_dst_destroy() is written in such a way that
> > it was not an issue thanks to the memset:
> > 
> > 	if (xdst->u.rt.dst.rt_uncached_list)
> > 		rt_del_uncached_list(&xdst->u.rt);
> > 
> > The route code does it the other way around: rt_uncached_list is
> > assumed to be valid IIF rt_uncached list_head is not empty:
> > 
> > void rt_del_uncached_list(struct rtable *rt)
> > {
> >         if (!list_empty(&rt->dst.rt_uncached)) {
> >                 struct uncached_list *ul = rt->dst.rt_uncached_list;
> > 
> >                 spin_lock_bh(&ul->lock);
> >                 list_del_init(&rt->dst.rt_uncached);
> >                 spin_unlock_bh(&ul->lock);
> >         }
> > }
> > 
> > This patch adds mandatory rt_uncached list_head initialization in
> > generic dst_init(), and adapt xfrm[46]_dst_destroy logic to match the
> > rest of the code.
> > 
> > Fixes: d288a162dd1c ("net: dst: Prevent false sharing vs. dst_entry:: __refcnt")
> > Signed-off-by: Maxime Bizon <mbizon@freebox.fr>
> > ---
> >  net/core/dst.c          | 1 +
> >  net/ipv4/xfrm4_policy.c | 4 +---
> >  net/ipv6/route.c        | 1 -
> >  net/ipv6/xfrm6_policy.c | 4 +---
> >  4 files changed, 3 insertions(+), 7 deletions(-)
> 
> It should go to net. Right now -rc7 is broken.
> 
> Also the change is not complete, you need to delete INIT_LIST_HEAD(..rt_uncached)
> from rt_dst_alloc and rt_dst_clone too.

It will be nice to give a credit to kbuild.
https://lore.kernel.org/all/202304162125.18b7bcdd-oliver.sang@intel.com

Thanks

> 
> Thanks