2024-04-23 12:03:17

by linke li

Subject: [PATCH] netfilter: mark racy access on ext->gen_id

In __nf_ct_ext_find(), ext->gen_id can be changed by
nf_ct_ext_valid_post(), using WRITE_ONCE. Mark data races on ext->gen_id
as benign using READ_ONCE.

This patch is aimed at reducing the number of benign races reported by
KCSAN in order to focus future debugging effort on harmful races.

Signed-off-by: linke li <[email protected]>
---
net/netfilter/nf_conntrack_extend.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nf_conntrack_extend.c b/net/netfilter/nf_conntrack_extend.c
index dd62cc12e775..7f1a5e5f6646 100644
--- a/net/netfilter/nf_conntrack_extend.c
+++ b/net/netfilter/nf_conntrack_extend.c
@@ -141,7 +141,7 @@ void *__nf_ct_ext_find(const struct nf_ct_ext *ext, u8 id)
if (!__nf_ct_ext_exist(ext, id))
return NULL;

- if (this_id == 0 || ext->gen_id == gen_id)
+ if (this_id == 0 || READ_ONCE(ext->gen_id) == gen_id)
return (void *)ext + ext->offset[id];

return NULL;
--
2.39.3 (Apple Git-146)

2024-04-23 12:08:24

by Florian Westphal

Subject: Re: [PATCH] netfilter: mark racy access on ext->gen_id

linke li <[email protected]> wrote:
> In __nf_ct_ext_find(), ext->gen_id can be changed by
> nf_ct_ext_valid_post(), using WRITE_ONCE. Mark data races on ext->gen_id
> as benign using READ_ONCE.
>
> This patch is aimed at reducing the number of benign races reported by
> KCSAN in order to focus future debugging effort on harmful races.

Acked-by: Florian Westphal <[email protected]>

Should proably go to nf tree.

2024-04-24 22:20:27

by Pablo Neira Ayuso

Subject: Re: [PATCH] netfilter: mark racy access on ext->gen_id

On Tue, Apr 23, 2024 at 02:03:09PM +0200, Florian Westphal wrote:
> linke li <[email protected]> wrote:
> > In __nf_ct_ext_find(), ext->gen_id can be changed by
> > nf_ct_ext_valid_post(), using WRITE_ONCE. Mark data races on ext->gen_id
> > as benign using READ_ONCE.
> >
> > This patch is aimed at reducing the number of benign races reported by
> > KCSAN in order to focus future debugging effort on harmful races.
>
> Acked-by: Florian Westphal <[email protected]>
>
> Should proably go to nf tree.

Can I get a Fixes: tag for this one?

2024-04-25 09:37:12

by Pablo Neira Ayuso

Subject: Re: [PATCH] netfilter: mark racy access on ext->gen_id

On Tue, Apr 23, 2024 at 07:50:22PM +0800, linke li wrote:
> In __nf_ct_ext_find(), ext->gen_id can be changed by
> nf_ct_ext_valid_post(), using WRITE_ONCE. Mark data races on ext->gen_id
> as benign using READ_ONCE.
>
> This patch is aimed at reducing the number of benign races reported by
> KCSAN in order to focus future debugging effort on harmful races.

There are a more uses ext->gen_id in the code, my understanding this
patch is just a stub.