Re: [PATCH] xfrm: clear mode callbacks after failed mode setup

[Cen Zhang]

Hi all,

Sorry for the noise, but I wanted to gently follow up on this patch in
case it got buried.

I would really appreciate any feedback when you have a chance. Please
let me know if I should make any changes or provide more testing
results.

Thanks a lot.

Best regards,
Cen Zhang

Cen Zhang <zzzccc427@xxxxxxxxx> 于2026年6月27日周六 11:01写道：
>
> xfrm_state_gc_task can run long after a failed IPTFS state setup. In the
> reproduced case, __xfrm_init_state() cached x->mode_cbs, IPTFS setup
> returned -ENOMEM before publishing mode_data, and the temporary module
> reference from xfrm_get_mode_cbs() was dropped immediately. The dead state
> then kept x->mode_cbs until deferred GC ran after xfrm_iptfs had been
> unloaded.
>
> Clear x->mode_cbs when mode init or clone fails before publishing
> mode_data. Those states never installed mode-specific state or the
> long-term IPTFS module pin, so deferred GC has nothing mode-specific to
> destroy and must not retain a callback table pointer past the temporary
> lookup reference.
>
> The buggy scenario involves two paths, with each column showing the order
> within that path:
>
> failed setup path:
> 1. cache x->mode_cbs
> 2. mode setup fails before mode_data
> 3. drop the temporary module ref
> 4. dead state keeps x->mode_cbs cached
>
> GC/unload path:
> 1. xfrm_state_put() queues GC work
> 2. xfrm_iptfs unloads later
> 3. xfrm_state_gc_task runs
> 4. GC dereferences stale x->mode_cbs
>
> This also covers the failed clone path where clone_state() returns before
> publishing mode_data.
>
> Validation reproduced this kernel report:
> Kernel panic - not syncing: Fatal exception
> CONFIG_FAULT_INJECTION_STACKTRACE_FILTER=y
> failslab_stacktrace_filter matched xfrm_iptfs frames
> ack_error=-12
> FAULT_INJECTION: forcing a failure
> BUG: unable to handle page fault
> Workqueue: events xfrm_state_gc_task
> RIP: xfrm_state_gc_task+0x142/0x650
> Modules linked in: esp4_offload xfrm_user [last unloaded: xfrm_iptfs]
> Kernel panic - not syncing: Fatal exception
>
> Fixes: 4b3faf610cc6 ("xfrm: iptfs: add new iptfs xfrm mode impl")
> Assisted-by: Codex:gpt-5.5
> Signed-off-by: Cen Zhang <zzzccc427@xxxxxxxxx>
> ---
>  net/xfrm/xfrm_state.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
> index c58cd024e3c6..4d95b2720894 100644
> --- a/net/xfrm/xfrm_state.c
> +++ b/net/xfrm/xfrm_state.c
> @@ -2071,8 +2071,11 @@ static struct xfrm_state *xfrm_state_clone_and_setup(struct xfrm_state *orig,
>
>         x->mode_cbs = orig->mode_cbs;
>         if (x->mode_cbs && x->mode_cbs->clone_state) {
> -               if (x->mode_cbs->clone_state(x, orig))
> +               if (x->mode_cbs->clone_state(x, orig)) {
> +                       if (!x->mode_data)
> +                               x->mode_cbs = NULL;
>                         goto error;
> +               }
>         }
>
>         x->props.reqid = m->new_reqid;
> @@ -3291,6 +3294,8 @@ int __xfrm_init_state(struct xfrm_state *x, struct netlink_ext_ack *extack)
>                 if (x->mode_cbs->init_state)
>                         err = x->mode_cbs->init_state(x);
>                 module_put(x->mode_cbs->owner);
> +               if (err && !x->mode_data)
> +                       x->mode_cbs = NULL;
>         }
>  error:
>         return err;
> --
> 2.43.0
>