Re: [PATCH] nfsd: Initialize ssc before laundromat_work to prevent NULL dereference

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2025-04-14 at 22:38 +0800, Li Lingfeng wrote:
> In nfs4_state_start_net(), laundromat_work may access nfsd_ssc through
> nfs4_laundromat -> nfsd4_ssc_expire_umount. If nfsd_ssc isn't initialized,
> this can cause NULL pointer dereference.
> 
> Normally the delayed start of laundromat_work allows sufficient time for
> nfsd_ssc initialization to complete. However, when the kernel waits too
> long for userspace responses (e.g. in nfs4_state_start_net ->
> nfsd4_end_grace -> nfsd4_record_grace_done -> nfsd4_cld_grace_done ->
> cld_pipe_upcall -> __cld_pipe_upcall -> wait_for_completion path), the
> delayed work may start before nfsd_ssc initialization finishes.
> 
> Fix this by moving nfsd_ssc initialization before starting laundromat_work.
> 
> Fixes: f4e44b393389 ("NFSD: delay unmount source's export after inter-server copy completed.")
> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
> ---
>  fs/nfsd/nfssvc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> index 9b3d6cff0e1e..8ed143ef8b41 100644
> --- a/fs/nfsd/nfssvc.c
> +++ b/fs/nfsd/nfssvc.c
> @@ -396,13 +396,13 @@ static int nfsd_startup_net(struct net *net, const struct cred *cred)
>  	if (ret)
>  		goto out_filecache;
>  
> +#ifdef CONFIG_NFSD_V4_2_INTER_SSC
> +	nfsd4_ssc_init_umount_work(nn);
> +#endif
>  	ret = nfs4_state_start_net(net);
>  	if (ret)
>  		goto out_reply_cache;
>  
> -#ifdef CONFIG_NFSD_V4_2_INTER_SSC
> -	nfsd4_ssc_init_umount_work(nn);
> -#endif
>  	nn->nfsd_net_up = true;
>  	return 0;
>  

Reviewed-by: Jeff Layton <jlayton@kernel.org>