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Date:   Mon, 17 Aug 2020 18:27:58 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     KP Singh <kpsingh@...omium.org>
CC:     <linux-kernel@...r.kernel.org>, <bpf@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Paul Turner <pjt@...gle.com>, Jann Horn <jannh@...gle.com>,
        Florent Revest <revest@...omium.org>
Subject: Re: [PATCH bpf-next v8 5/7] bpf: Implement bpf_local_storage for
 inodes

On Mon, Aug 03, 2020 at 06:46:53PM +0200, KP Singh wrote:
> From: KP Singh <kpsingh@...gle.com>
> 
> Similar to bpf_local_storage for sockets, add local storage for inodes.
> The life-cycle of storage is managed with the life-cycle of the inode.
> i.e. the storage is destroyed along with the owning inode.
> 
> The BPF LSM allocates an __rcu pointer to the bpf_local_storage in the
> security blob which are now stackable and can co-exist with other LSMs.
> 
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> ---
>  include/linux/bpf_local_storage.h             |  10 +
>  include/linux/bpf_lsm.h                       |  21 ++
>  include/linux/bpf_types.h                     |   3 +
>  include/uapi/linux/bpf.h                      |  38 +++
>  kernel/bpf/Makefile                           |   1 +
>  kernel/bpf/bpf_inode_storage.c                | 265 ++++++++++++++++++
>  kernel/bpf/syscall.c                          |   3 +-
>  kernel/bpf/verifier.c                         |  10 +
>  security/bpf/hooks.c                          |   7 +
>  .../bpf/bpftool/Documentation/bpftool-map.rst |   2 +-
>  tools/bpf/bpftool/bash-completion/bpftool     |   3 +-
>  tools/bpf/bpftool/map.c                       |   3 +-
>  tools/include/uapi/linux/bpf.h                |  38 +++
>  tools/lib/bpf/libbpf_probes.c                 |   5 +-
>  14 files changed, 403 insertions(+), 6 deletions(-)
>  create mode 100644 kernel/bpf/bpf_inode_storage.c
> 
> diff --git a/include/linux/bpf_local_storage.h b/include/linux/bpf_local_storage.h
> index 3685f681a7fc..75c76847fad5 100644
> --- a/include/linux/bpf_local_storage.h
> +++ b/include/linux/bpf_local_storage.h
> @@ -160,4 +160,14 @@ struct bpf_local_storage_data *
>  bpf_local_storage_update(void *owner, struct bpf_map *map, void *value,
>  			 u64 map_flags);
>  
> +#ifdef CONFIG_BPF_LSM
> +extern const struct bpf_func_proto bpf_inode_storage_get_proto;
> +extern const struct bpf_func_proto bpf_inode_storage_delete_proto;
> +void bpf_inode_storage_free(struct inode *inode);
> +#else
> +static inline void bpf_inode_storage_free(struct inode *inode)
> +{
> +}
> +#endif /* CONFIG_BPF_LSM */
This is LSM specific.  Can they be moved to bpf_lsm.h?

> +
>  #endif /* _BPF_LOCAL_STORAGE_H */
> diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
> index af74712af585..d0683ada1e49 100644
> --- a/include/linux/bpf_lsm.h
> +++ b/include/linux/bpf_lsm.h
> @@ -17,9 +17,24 @@
>  #include <linux/lsm_hook_defs.h>
>  #undef LSM_HOOK
>  
> +struct bpf_storage_blob {
> +	struct bpf_local_storage __rcu *storage;
> +};
> +
> +extern struct lsm_blob_sizes bpf_lsm_blob_sizes;
> +
>  int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
>  			const struct bpf_prog *prog);
>  
> +static inline struct bpf_storage_blob *bpf_inode(
> +	const struct inode *inode)
> +{
> +	if (unlikely(!inode->i_security))
> +		return NULL;
> +
> +	return inode->i_security + bpf_lsm_blob_sizes.lbs_inode;
> +}
> +
>  #else /* !CONFIG_BPF_LSM */
>  
>  static inline int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
> @@ -28,6 +43,12 @@ static inline int bpf_lsm_verify_prog(struct bpf_verifier_log *vlog,
>  	return -EOPNOTSUPP;
>  }
>  
> +static inline struct bpf_storage_blob *bpf_inode(
> +	const struct inode *inode)
> +{
> +	return NULL;
> +}
> +
>  #endif /* CONFIG_BPF_LSM */
>  
>  #endif /* _LINUX_BPF_LSM_H */

[ ... ]

> diff --git a/kernel/bpf/bpf_inode_storage.c b/kernel/bpf/bpf_inode_storage.c
> new file mode 100644
> index 000000000000..a51a6328c02d
> --- /dev/null
> +++ b/kernel/bpf/bpf_inode_storage.c
> @@ -0,0 +1,265 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2019 Facebook
> + * Copyright 2020 Google LLC.
> + */
> +
> +#include <linux/rculist.h>
> +#include <linux/list.h>
> +#include <linux/hash.h>
> +#include <linux/types.h>
> +#include <linux/spinlock.h>
> +#include <linux/bpf.h>
> +#include <linux/bpf_local_storage.h>
> +#include <net/sock.h>
> +#include <uapi/linux/sock_diag.h>
> +#include <uapi/linux/btf.h>
> +#include <linux/bpf_lsm.h>
> +#include <linux/btf_ids.h>
> +#include <linux/fdtable.h>
> +
> +DEFINE_BPF_STORAGE_CACHE(inode_cache);
> +
> +static struct bpf_local_storage __rcu **
> +inode_storage_ptr(void *owner)
> +{
> +	struct inode *inode = owner;
> +	struct bpf_storage_blob *bsb;
> +	bsb = bpf_inode(inode);
> +	if (!bsb)
> +		return NULL;
> +	return &bsb->storage;
> +}
> +
> +static struct bpf_local_storage_data *inode_storage_lookup(struct inode *inode,
> +							   struct bpf_map *map,
> +							   bool cacheit_lockit)
> +{
> +	struct bpf_local_storage *inode_storage;
> +	struct bpf_local_storage_map *smap;
> +	struct bpf_storage_blob *bsb;
> +
> +	bsb = bpf_inode(inode);
> +	if (!bsb)
> +		return ERR_PTR(-ENOENT);
ERR_PTR is returned here...

> +
> +	inode_storage = rcu_dereference(bsb->storage);
> +	if (!inode_storage)
> +		return NULL;
> +
> +	smap = (struct bpf_local_storage_map *)map;
> +	return bpf_local_storage_lookup(inode_storage, smap, cacheit_lockit);
> +}
> +
> +void bpf_inode_storage_free(struct inode *inode)
> +{
> +	struct bpf_local_storage_elem *selem;
> +	struct bpf_local_storage *local_storage;
> +	bool free_inode_storage = false;
> +	struct bpf_storage_blob *bsb;
> +	struct hlist_node *n;
> +
> +	bsb = bpf_inode(inode);
> +	if (!bsb)
> +		return;
> +
> +	rcu_read_lock();
> +
> +	local_storage = rcu_dereference(bsb->storage);
> +	if (!local_storage) {
> +		rcu_read_unlock();
> +		return;
> +	}
> +
> +	/* Netiher the bpf_prog nor the bpf-map's syscall
> +	 * could be modifying the local_storage->list now.
> +	 * Thus, no elem can be added-to or deleted-from the
> +	 * local_storage->list by the bpf_prog or by the bpf-map's syscall.
> +	 *
> +	 * It is racing with bpf_local_storage_map_free() alone
> +	 * when unlinking elem from the local_storage->list and
> +	 * the map's bucket->list.
> +	 */
> +	raw_spin_lock_bh(&local_storage->lock);
> +	hlist_for_each_entry_safe(selem, n, &local_storage->list, snode) {
> +		/* Always unlink from map before unlinking from
> +		 * local_storage.
> +		 */
> +		bpf_selem_unlink_map(selem);
> +		free_inode_storage =
> +			bpf_selem_unlink_storage(local_storage, selem, false);
> +	}
> +	raw_spin_unlock_bh(&local_storage->lock);
> +	rcu_read_unlock();
> +
> +	/* free_inoode_storage should always be true as long as
> +	 * local_storage->list was non-empty.
> +	 */
> +	if (free_inode_storage)
> +		kfree_rcu(local_storage, rcu);
> +}
> +
> +
> +static void *bpf_fd_inode_storage_lookup_elem(struct bpf_map *map, void *key)
> +{
> +	struct bpf_local_storage_data *sdata;
> +	struct file *f;
> +	int fd;
> +
> +	fd = *(int *)key;
> +	f = fcheck(fd);
> +	if (!f)
> +		return ERR_PTR(-EINVAL);
> +
> +	get_file(f);
> +	sdata = inode_storage_lookup(f->f_inode, map, true);
> +	fput(f);
> +	return sdata ? sdata->data : NULL;
sdata can be ERR_PTR here and a few other cases below.

May be inode_storage_lookup() should just return NULL.

> +}
> +
> +static int bpf_fd_inode_storage_update_elem(struct bpf_map *map, void *key,
> +					 void *value, u64 map_flags)
> +{
> +	struct bpf_local_storage_data *sdata;
> +	struct file *f;
> +	int fd;
> +
> +	fd = *(int *)key;
> +	f = fcheck(fd);
> +	if (!f)
> +		return -EINVAL;
> +
> +	get_file(f);
get_file() does atomic_long_inc() instead of atomic_long_inc_not_zero().
I don't see how that helps here.  Am I missing something?

> +	sdata = bpf_local_storage_update(f->f_inode, map, value, map_flags);
> +	fput(f);
> +	return PTR_ERR_OR_ZERO(sdata);
> +}
> +

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