// SPDX-License-Identifier: GPL-2.0
/*
* FUSE passthrough to backing file.
*
* Copyright (c) 2023 CTERA Networks.
*/
#include "fuse_i.h"
#include <linux/file.h>
#include <linux/backing-file.h>
#include <linux/splice.h>
static void fuse_file_accessed(struct file *file)
{
struct inode *inode = file_inode(file);
fuse_invalidate_atime(inode);
}
static void fuse_file_modified(struct file *file)
{
struct inode *inode = file_inode(file);
fuse_invalidate_attr_mask(inode, FUSE_STATX_MODSIZE);
}
ssize_t fuse_passthrough_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
struct file *file = iocb->ki_filp;
struct fuse_file *ff = file->private_data;
struct file *backing_file = fuse_file_passthrough(ff);
size_t count = iov_iter_count(iter);
ssize_t ret;
struct backing_file_ctx ctx = {
.cred = ff->cred,
.user_file = file,
.accessed = fuse_file_accessed,
};
pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__,
backing_file, iocb->ki_pos, count);
if (!count)
return 0;
ret = backing_file_read_iter(backing_file, iter, iocb, iocb->ki_flags,
&ctx);
return ret;
}
ssize_t fuse_passthrough_write_iter(struct kiocb *iocb,
struct iov_iter *iter)
{
struct file *file = iocb->ki_filp;
struct inode *inode = file_inode(file);
struct fuse_file *ff = file->private_data;
struct file *backing_file = fuse_file_passthrough(ff);
size_t count = iov_iter_count(iter);
ssize_t ret;
struct backing_file_ctx ctx = {
.cred = ff->cred,
.user_file = file,
.end_write = fuse_file_modified,
};
pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__,
backing_file, iocb->ki_pos, count);
if (!count)
return 0;
inode_lock(inode);
ret = backing_file_write_iter(backing_file, iter, iocb, iocb->ki_flags,
&ctx);
inode_unlock(inode);
return ret;
}
ssize_t fuse_passthrough_splice_read(struct file *in, loff_t *ppos,
struct pipe_inode_info *pipe,
size_t len, unsigned int flags)
{
struct fuse_file *ff = in->private_data;
struct file *backing_file = fuse_file_passthrough(ff);
struct backing_file_ctx ctx = {
.cred = ff->cred,
.user_file = in,
.accessed = fuse_file_accessed,
};
pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu, flags=0x%x\n", __func__,
backing_file, ppos ? *ppos : 0, len, flags);
return backing_file_splice_read(backing_file, ppos, pipe, len, flags,
&ctx);
}
ssize_t fuse_passthrough_splice_write(struct pipe_inode_info *pipe,
struct file *out, loff_t *ppos,
size_t len, unsigned int flags)
{
struct fuse_file *ff = out->private_data;
struct file *backing_file = fuse_file_passthrough(ff);
struct inode *inode = file_inode(out);
ssize_t ret;
struct backing_file_ctx ctx = {
.cred = ff->cred,
.user_file = out,
.end_write = fuse_file_modified,
};
pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu, flags=0x%x\n", __func__,
backing_file, ppos ? *ppos : 0, len, flags);
inode_lock(inode);
ret = backing_file_splice_write(pipe, backing_file, ppos, len, flags,
&ctx);
inode_unlock(inode);
return ret;
}
ssize_t fuse_passthrough_mmap(struct file *file, struct vm_area_struct *vma)
{
struct fuse_file *ff = file->private_data;
struct file *backing_file = fuse_file_passthrough(ff);
struct backing_file_ctx ctx = {
.cred = ff->cred,
.user_file = file,
.accessed = fuse_file_accessed,
};
pr_debug("%s: backing_file=0x%p, start=%lu, end=%lu\n", __func__,
backing_file, vma->vm_start, vma->vm_end);
return backing_file_mmap(backing_file, vma, &ctx);
}
struct fuse_backing *fuse_backing_get(struct fuse_backing *fb)
{
if (fb && refcount_inc_not_zero(&fb->count))
return fb;
return NULL;
}
static void fuse_backing_free(struct fuse_backing *fb)
{
pr_debug("%s: fb=0x%p\n", __func__, fb);
if (fb->file)
fput(fb->file);
put_cred(fb->cred);
kfree_rcu(fb, rcu);
}
void fuse_backing_put(struct fuse_backing *fb)
{
if (fb && refcount_dec_and_test(&fb->count))
fuse_backing_free(fb);
}
void fuse_backing_files_init(struct fuse_conn *fc)
{
idr_init(&fc->backing_files_map);
}
static int fuse_backing_id_alloc(struct fuse_conn *fc, struct fuse_backing *fb)
{
int id;
idr_preload(GFP_KERNEL);
spin_lock(&fc->lock);
/* FIXME: xarray might be space inefficient */
id = idr_alloc_cyclic(&fc->backing_files_map, fb, 1, 0, GFP_ATOMIC);
spin_unlock(&fc->lock);
idr_preload_end();
WARN_ON_ONCE(id == 0);
return id;
}
static struct fuse_backing *fuse_backing_id_remove(struct fuse_conn *fc,
int id)
{
struct fuse_backing *fb;
spin_lock(&fc->lock);
fb = idr_remove(&fc->backing_files_map, id);
spin_unlock(&fc->lock);
return fb;
}
static int fuse_backing_id_free(int id, void *p, void *data)
{
struct fuse_backing *fb = p;
WARN_ON_ONCE(refcount_read(&fb->count) != 1);
fuse_backing_free(fb);
return 0;
}
void fuse_backing_files_free(struct fuse_conn *fc)
{
idr_for_each(&fc->backing_files_map, fuse_backing_id_free, NULL);
idr_destroy(&fc->backing_files_map);
}
int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
{
struct file *file;
struct super_block *backing_sb;
struct fuse_backing *fb = NULL;
int res;
pr_debug("%s: fd=%d flags=0x%x\n", __func__, map->fd, map->flags);
/* TODO: relax CAP_SYS_ADMIN once backing files are visible to lsof */
res = -EPERM;
if (!fc->passthrough || !capable(CAP_SYS_ADMIN))
goto out;
res = -EINVAL;
if (map->flags || map->padding)
goto out;
file = fget_raw(map->fd);
res = -EBADF;
if (!file)
goto out;
backing_sb = file_inode(file)->i_sb;
pr_info("%s: %x:%pD %i\n", __func__, backing_sb->s_dev, file, backing_sb->s_stack_depth);
res = -ELOOP;
if (backing_sb->s_stack_depth >= fc->max_stack_depth)
goto out_fput;
fb = kmalloc(sizeof(struct fuse_backing), GFP_KERNEL);
res = -ENOMEM;
if (!fb)
goto out_fput;
fb->file = file;
fb->cred = prepare_creds();
refcount_set(&fb->count, 1);
res = fuse_backing_id_alloc(fc, fb);
if (res < 0) {
fuse_backing_free(fb);
fb = NULL;
}
out:
pr_debug("%s: fb=0x%p, ret=%i\n", __func__, fb, res);
return res;
out_fput:
fput(file);
goto out;
}
int fuse_backing_close(struct fuse_conn *fc, int backing_id)
{
struct fuse_backing *fb = NULL;
int err;
pr_debug("%s: backing_id=%d\n", __func__, backing_id);
/* TODO: relax CAP_SYS_ADMIN once backing files are visible to lsof */
err = -EPERM;
if (!fc->passthrough || !capable(CAP_SYS_ADMIN))
goto out;
err = -EINVAL;
if (backing_id <= 0)
goto out;
err = -ENOENT;
fb = fuse_backing_id_remove(fc, backing_id);
if (!fb)
goto out;
fuse_backing_put(fb);
err = 0;
out:
pr_debug("%s: fb=0x%p, err=%i\n", __func__, fb, err);
return err;
}
/*
* Setup passthrough to a backing file.
*
* Returns an fb object with elevated refcount to be stored in fuse inode.
*/
struct fuse_backing *fuse_passthrough_open(struct file *file,
struct inode *inode,
int backing_id)
{
struct fuse_file *ff = file->private_data;
struct fuse_conn *fc = ff->fm->fc;
struct fuse_backing *fb = NULL;
struct file *backing_file;
int err;
err = -EINVAL;
if (backing_id <= 0)
goto out;
rcu_read_lock();
fb = idr_find(&fc->backing_files_map, backing_id);
fb = fuse_backing_get(fb);
rcu_read_unlock();
err = -ENOENT;
if (!fb)
goto out;
/* Allocate backing file per fuse file to store fuse path */
backing_file = backing_file_open(&file->f_path, file->f_flags,
&fb->file->f_path, fb->cred);
err = PTR_ERR(backing_file);
if (IS_ERR(backing_file)) {
fuse_backing_put(fb);
goto out;
}
err = 0;
ff->passthrough = backing_file;
ff->cred = get_cred(fb->cred);
out:
pr_debug("%s: backing_id=%d, fb=0x%p, backing_file=0x%p, err=%i\n", __func__,
backing_id, fb, ff->passthrough, err);
return err ? ERR_PTR(err) : fb;
}
void fuse_passthrough_release(struct fuse_file *ff, struct fuse_backing *fb)
{
pr_debug("%s: fb=0x%p, backing_file=0x%p\n", __func__,
fb, ff->passthrough);
fput(ff->passthrough);
ff->passthrough = NULL;
put_cred(ff->cred);
ff->cred = NULL;
}
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