Re: [PATCH 1/1] NFSD: fix problems with cleanup on errors in nfsd4_copy

[Jeff Layton <jlayton@xxxxxxxxxx>]

On Mon, 2023-01-23 at 21:32 -0800, Dai Ngo wrote:
> When nfsd4_copy fails to allocate memory for async_copy->cp_src, or
> nfs4_init_copy_state fails, it calls cleanup_async_copy to do the
> cleanup for the async_copy which causes page fault since async_copy
> is not yet initialized.
> 
> This patche sets async_copy to NULL to skip cleanup_async_copy
> if async_copy is not yet initialized.
> 
> Fixes: ce0887ac96d3 ("NFSD add nfs4 inter ssc to nfsd4_copy")
> Fixes: 87689df69491 ("NFSD: Shrink size of struct nfsd4_copy")
> Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
> ---
>  fs/nfsd/nfs4proc.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index 3b73e4d342bf..b4e7e18e1761 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -1688,7 +1688,8 @@ static void cleanup_async_copy(struct nfsd4_copy *copy)
>  	if (!nfsd4_ssc_is_inter(copy))
>  		nfsd_file_put(copy->nf_src);
>  	spin_lock(&copy->cp_clp->async_lock);
> -	list_del(&copy->copies);
> +	if (!list_empty(&copy->copies))
> +		list_del(&copy->copies);
>  	spin_unlock(&copy->cp_clp->async_lock);
>  	nfs4_put_copy(copy);
>  }
> @@ -1789,9 +1790,15 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  			goto out_err;
>  		async_copy->cp_src = kmalloc(sizeof(*async_copy->cp_src), GFP_KERNEL);
>  		if (!async_copy->cp_src)
> +			goto no_mem;
> +		if (!nfs4_init_copy_state(nn, copy)) {
> +			kfree(async_copy->cp_src);
> +no_mem:
> +			kfree(async_copy);
> +			async_copy = NULL;

This seems pretty fragile and the result begins to resemble spaghetti. I
think it'd be cleaner to initialize the list_head and refcount before
you do the allocation of cp_src. Then you can just call
cleanup_async_copy no matter where it fails.

Bear in mind that these are failure codepaths, so we don't need to
optimize for performance here.



>  			goto out_err;
> -		if (!nfs4_init_copy_state(nn, copy))
> -			goto out_err;
> +		}
> +		INIT_LIST_HEAD(&async_copy->copies);
>  		refcount_set(&async_copy->refcount, 1);
>  		memcpy(&copy->cp_res.cb_stateid, &copy->cp_stateid.cs_stid,
>  			sizeof(copy->cp_res.cb_stateid));

-- 
Jeff Layton <jlayton@xxxxxxxxxx>