bpf_fs_kfuncs.c | Explore in Territory

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2024 Google LLC. */

#include <linux/bpf.h>
#include <linux/btf.h>
#include <linux/btf_ids.h>
#include <linux/dcache.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/xattr.h>

__bpf_kfunc_start_defs();

/**
 * bpf_get_task_exe_file - get a reference on the exe_file struct file member of
 *                         the mm_struct that is nested within the supplied
 *                         task_struct
 * @task: task_struct of which the nested mm_struct exe_file member to get a
 * reference on
 *
 * Get a reference on the exe_file struct file member field of the mm_struct
 * nested within the supplied *task*. The referenced file pointer acquired by
 * this BPF kfunc must be released using bpf_put_file(). Failing to call
 * bpf_put_file() on the returned referenced struct file pointer that has been
 * acquired by this BPF kfunc will result in the BPF program being rejected by
 * the BPF verifier.
 *
 * This BPF kfunc may only be called from BPF LSM programs.
 *
 * Internally, this BPF kfunc leans on get_task_exe_file(), such that calling
 * bpf_get_task_exe_file() would be analogous to calling get_task_exe_file()
 * directly in kernel context.
 *
 * Return: A referenced struct file pointer to the exe_file member of the
 * mm_struct that is nested within the supplied *task*. On error, NULL is
 * returned.
 */
__bpf_kfunc struct file *bpf_get_task_exe_file(struct task_struct *task)
{ … }

/**
 * bpf_put_file - put a reference on the supplied file
 * @file: file to put a reference on
 *
 * Put a reference on the supplied *file*. Only referenced file pointers may be
 * passed to this BPF kfunc. Attempting to pass an unreferenced file pointer, or
 * any other arbitrary pointer for that matter, will result in the BPF program
 * being rejected by the BPF verifier.
 *
 * This BPF kfunc may only be called from BPF LSM programs.
 */
__bpf_kfunc void bpf_put_file(struct file *file)
{ … }

/**
 * bpf_path_d_path - resolve the pathname for the supplied path
 * @path: path to resolve the pathname for
 * @buf: buffer to return the resolved pathname in
 * @buf__sz: length of the supplied buffer
 *
 * Resolve the pathname for the supplied *path* and store it in *buf*. This BPF
 * kfunc is the safer variant of the legacy bpf_d_path() helper and should be
 * used in place of bpf_d_path() whenever possible. It enforces KF_TRUSTED_ARGS
 * semantics, meaning that the supplied *path* must itself hold a valid
 * reference, or else the BPF program will be outright rejected by the BPF
 * verifier.
 *
 * This BPF kfunc may only be called from BPF LSM programs.
 *
 * Return: A positive integer corresponding to the length of the resolved
 * pathname in *buf*, including the NUL termination character. On error, a
 * negative integer is returned.
 */
__bpf_kfunc int bpf_path_d_path(struct path *path, char *buf, size_t buf__sz)
{ … }

/**
 * bpf_get_dentry_xattr - get xattr of a dentry
 * @dentry: dentry to get xattr from
 * @name__str: name of the xattr
 * @value_p: output buffer of the xattr value
 *
 * Get xattr *name__str* of *dentry* and store the output in *value_ptr*.
 *
 * For security reasons, only *name__str* with prefix "user." is allowed.
 *
 * Return: 0 on success, a negative value on error.
 */
__bpf_kfunc int bpf_get_dentry_xattr(struct dentry *dentry, const char *name__str,
				     struct bpf_dynptr *value_p)
{ … }

/**
 * bpf_get_file_xattr - get xattr of a file
 * @file: file to get xattr from
 * @name__str: name of the xattr
 * @value_p: output buffer of the xattr value
 *
 * Get xattr *name__str* of *file* and store the output in *value_ptr*.
 *
 * For security reasons, only *name__str* with prefix "user." is allowed.
 *
 * Return: 0 on success, a negative value on error.
 */
__bpf_kfunc int bpf_get_file_xattr(struct file *file, const char *name__str,
				   struct bpf_dynptr *value_p)
{ … }

__bpf_kfunc_end_defs();

BTF_KFUNCS_START(bpf_fs_kfunc_set_ids)
BTF_ID_FLAGS(…)
BTF_ID_FLAGS(…)
BTF_ID_FLAGS(…)
BTF_ID_FLAGS(…)
BTF_ID_FLAGS(…)
BTF_KFUNCS_END(…)

static int bpf_fs_kfuncs_filter(const struct bpf_prog *prog, u32 kfunc_id)
{ … }

static const struct btf_kfunc_id_set bpf_fs_kfunc_set = …;

static int __init bpf_fs_kfuncs_init(void)
{ … }

late_initcall(bpf_fs_kfuncs_init);
linux/fs/bpf_fs_kfuncs.c
