linux-kernel - Re: [PATCH v2 bpf-next 3/4] bpf: Add recursion prevention logic for inode storage

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Message-ID: <c2239508-6d00-4176-b0d6-3e07e06a367f@linux.dev>
Date: Tue, 12 Nov 2024 15:26:43 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Song Liu <song@...nel.org>
Cc: bpf@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org,
 kernel-team@...a.com, andrii@...nel.org, eddyz87@...il.com, ast@...nel.org,
 daniel@...earbox.net, viro@...iv.linux.org.uk, brauner@...nel.org,
 jack@...e.cz, kpsingh@...nel.org, mattbobrowski@...gle.com,
 amir73il@...il.com, repnop@...gle.com, jlayton@...nel.org,
 josef@...icpanda.com, mic@...ikod.net, gnoack@...gle.com
Subject: Re: [PATCH v2 bpf-next 3/4] bpf: Add recursion prevention logic for
 inode storage

On 11/12/24 12:36 AM, Song Liu wrote:
> +static void *__bpf_inode_storage_get(struct bpf_map *map, struct inode *inode,
> +				     void *value, u64 flags, gfp_t gfp_flags, bool nobusy)
>   {
>   	struct bpf_local_storage_data *sdata;
>   
> -	WARN_ON_ONCE(!bpf_rcu_lock_held());
> -	if (flags & ~(BPF_LOCAL_STORAGE_GET_F_CREATE))
> -		return (unsigned long)NULL;
> -
> +	/* explicitly check that the inode not NULL */
>   	if (!inode)
> -		return (unsigned long)NULL;
> +		return NULL;
>   
>   	sdata = inode_storage_lookup(inode, map, true);

s/true/nobusy/

>   	if (sdata)
> -		return (unsigned long)sdata->data;
> +		return sdata->data;
>   
> -	/* This helper must only called from where the inode is guaranteed
> -	 * to have a refcount and cannot be freed.
> -	 */
> -	if (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {
> +	/* only allocate new storage, when the inode is refcounted */
> +	if (atomic_read(&inode->i_count) &&
> +	    flags & BPF_LOCAL_STORAGE_GET_F_CREATE) {

	    (flags & BPF_LOCAL_STORAGE_GET_F_CREATE) && nobusy) {

>   		sdata = bpf_local_storage_update(
>   			inode, (struct bpf_local_storage_map *)map, value,
>   			BPF_NOEXIST, false, gfp_flags);
> -		return IS_ERR(sdata) ? (unsigned long)NULL :
> -					     (unsigned long)sdata->data;
> +		return IS_ERR(sdata) ? NULL : sdata->data;
>   	}
>   
> -	return (unsigned long)NULL;
> +	return NULL;
> +}