linux/fs/fuse/cuse.c
Seth Forshee 744742d692 fuse: Add reference counting for fuse_io_priv
The 'reqs' member of fuse_io_priv serves two purposes. First is to track
the number of oustanding async requests to the server and to signal that
the io request is completed. The second is to be a reference count on the
structure to know when it can be freed.

For sync io requests these purposes can be at odds.  fuse_direct_IO() wants
to block until the request is done, and since the signal is sent when
'reqs' reaches 0 it cannot keep a reference to the object. Yet it needs to
use the object after the userspace server has completed processing
requests. This leads to some handshaking and special casing that it
needlessly complicated and responsible for at least one race condition.

It's much cleaner and safer to maintain a separate reference count for the
object lifecycle and to let 'reqs' just be a count of outstanding requests
to the userspace server. Then we can know for sure when it is safe to free
the object without any handshaking or special cases.

The catch here is that most of the time these objects are stack allocated
and should not be freed. Initializing these objects with a single reference
that is never released prevents accidental attempts to free the objects.

Fixes: 9d5722b777 ("fuse: handle synchronous iocbs internally")
Cc: stable@vger.kernel.org # v4.1+
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-03-14 15:02:51 +01:00

646 lines
15 KiB
C

/*
* CUSE: Character device in Userspace
*
* Copyright (C) 2008-2009 SUSE Linux Products GmbH
* Copyright (C) 2008-2009 Tejun Heo <tj@kernel.org>
*
* This file is released under the GPLv2.
*
* CUSE enables character devices to be implemented from userland much
* like FUSE allows filesystems. On initialization /dev/cuse is
* created. By opening the file and replying to the CUSE_INIT request
* userland CUSE server can create a character device. After that the
* operation is very similar to FUSE.
*
* A CUSE instance involves the following objects.
*
* cuse_conn : contains fuse_conn and serves as bonding structure
* channel : file handle connected to the userland CUSE server
* cdev : the implemented character device
* dev : generic device for cdev
*
* Note that 'channel' is what 'dev' is in FUSE. As CUSE deals with
* devices, it's called 'channel' to reduce confusion.
*
* channel determines when the character device dies. When channel is
* closed, everything begins to destruct. The cuse_conn is taken off
* the lookup table preventing further access from cdev, cdev and
* generic device are removed and the base reference of cuse_conn is
* put.
*
* On each open, the matching cuse_conn is looked up and if found an
* additional reference is taken which is released when the file is
* closed.
*/
#include <linux/fuse.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/kthread.h>
#include <linux/list.h>
#include <linux/magic.h>
#include <linux/miscdevice.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/stat.h>
#include <linux/module.h>
#include <linux/uio.h>
#include "fuse_i.h"
#define CUSE_CONNTBL_LEN 64
struct cuse_conn {
struct list_head list; /* linked on cuse_conntbl */
struct fuse_conn fc; /* fuse connection */
struct cdev *cdev; /* associated character device */
struct device *dev; /* device representing @cdev */
/* init parameters, set once during initialization */
bool unrestricted_ioctl;
};
static DEFINE_MUTEX(cuse_lock); /* protects registration */
static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN];
static struct class *cuse_class;
static struct cuse_conn *fc_to_cc(struct fuse_conn *fc)
{
return container_of(fc, struct cuse_conn, fc);
}
static struct list_head *cuse_conntbl_head(dev_t devt)
{
return &cuse_conntbl[(MAJOR(devt) + MINOR(devt)) % CUSE_CONNTBL_LEN];
}
/**************************************************************************
* CUSE frontend operations
*
* These are file operations for the character device.
*
* On open, CUSE opens a file from the FUSE mnt and stores it to
* private_data of the open file. All other ops call FUSE ops on the
* FUSE file.
*/
static ssize_t cuse_read_iter(struct kiocb *kiocb, struct iov_iter *to)
{
struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb->ki_filp);
loff_t pos = 0;
return fuse_direct_io(&io, to, &pos, FUSE_DIO_CUSE);
}
static ssize_t cuse_write_iter(struct kiocb *kiocb, struct iov_iter *from)
{
struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(kiocb->ki_filp);
loff_t pos = 0;
/*
* No locking or generic_write_checks(), the server is
* responsible for locking and sanity checks.
*/
return fuse_direct_io(&io, from, &pos,
FUSE_DIO_WRITE | FUSE_DIO_CUSE);
}
static int cuse_open(struct inode *inode, struct file *file)
{
dev_t devt = inode->i_cdev->dev;
struct cuse_conn *cc = NULL, *pos;
int rc;
/* look up and get the connection */
mutex_lock(&cuse_lock);
list_for_each_entry(pos, cuse_conntbl_head(devt), list)
if (pos->dev->devt == devt) {
fuse_conn_get(&pos->fc);
cc = pos;
break;
}
mutex_unlock(&cuse_lock);
/* dead? */
if (!cc)
return -ENODEV;
/*
* Generic permission check is already done against the chrdev
* file, proceed to open.
*/
rc = fuse_do_open(&cc->fc, 0, file, 0);
if (rc)
fuse_conn_put(&cc->fc);
return rc;
}
static int cuse_release(struct inode *inode, struct file *file)
{
struct fuse_file *ff = file->private_data;
struct fuse_conn *fc = ff->fc;
fuse_sync_release(ff, file->f_flags);
fuse_conn_put(fc);
return 0;
}
static long cuse_file_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
struct fuse_file *ff = file->private_data;
struct cuse_conn *cc = fc_to_cc(ff->fc);
unsigned int flags = 0;
if (cc->unrestricted_ioctl)
flags |= FUSE_IOCTL_UNRESTRICTED;
return fuse_do_ioctl(file, cmd, arg, flags);
}
static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
struct fuse_file *ff = file->private_data;
struct cuse_conn *cc = fc_to_cc(ff->fc);
unsigned int flags = FUSE_IOCTL_COMPAT;
if (cc->unrestricted_ioctl)
flags |= FUSE_IOCTL_UNRESTRICTED;
return fuse_do_ioctl(file, cmd, arg, flags);
}
static const struct file_operations cuse_frontend_fops = {
.owner = THIS_MODULE,
.read_iter = cuse_read_iter,
.write_iter = cuse_write_iter,
.open = cuse_open,
.release = cuse_release,
.unlocked_ioctl = cuse_file_ioctl,
.compat_ioctl = cuse_file_compat_ioctl,
.poll = fuse_file_poll,
.llseek = noop_llseek,
};
/**************************************************************************
* CUSE channel initialization and destruction
*/
struct cuse_devinfo {
const char *name;
};
/**
* cuse_parse_one - parse one key=value pair
* @pp: i/o parameter for the current position
* @end: points to one past the end of the packed string
* @keyp: out parameter for key
* @valp: out parameter for value
*
* *@pp points to packed strings - "key0=val0\0key1=val1\0" which ends
* at @end - 1. This function parses one pair and set *@keyp to the
* start of the key and *@valp to the start of the value. Note that
* the original string is modified such that the key string is
* terminated with '\0'. *@pp is updated to point to the next string.
*
* RETURNS:
* 1 on successful parse, 0 on EOF, -errno on failure.
*/
static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp)
{
char *p = *pp;
char *key, *val;
while (p < end && *p == '\0')
p++;
if (p == end)
return 0;
if (end[-1] != '\0') {
printk(KERN_ERR "CUSE: info not properly terminated\n");
return -EINVAL;
}
key = val = p;
p += strlen(p);
if (valp) {
strsep(&val, "=");
if (!val)
val = key + strlen(key);
key = strstrip(key);
val = strstrip(val);
} else
key = strstrip(key);
if (!strlen(key)) {
printk(KERN_ERR "CUSE: zero length info key specified\n");
return -EINVAL;
}
*pp = p;
*keyp = key;
if (valp)
*valp = val;
return 1;
}
/**
* cuse_parse_dev_info - parse device info
* @p: device info string
* @len: length of device info string
* @devinfo: out parameter for parsed device info
*
* Parse @p to extract device info and store it into @devinfo. String
* pointed to by @p is modified by parsing and @devinfo points into
* them, so @p shouldn't be freed while @devinfo is in use.
*
* RETURNS:
* 0 on success, -errno on failure.
*/
static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo)
{
char *end = p + len;
char *uninitialized_var(key), *uninitialized_var(val);
int rc;
while (true) {
rc = cuse_parse_one(&p, end, &key, &val);
if (rc < 0)
return rc;
if (!rc)
break;
if (strcmp(key, "DEVNAME") == 0)
devinfo->name = val;
else
printk(KERN_WARNING "CUSE: unknown device info \"%s\"\n",
key);
}
if (!devinfo->name || !strlen(devinfo->name)) {
printk(KERN_ERR "CUSE: DEVNAME unspecified\n");
return -EINVAL;
}
return 0;
}
static void cuse_gendev_release(struct device *dev)
{
kfree(dev);
}
/**
* cuse_process_init_reply - finish initializing CUSE channel
*
* This function creates the character device and sets up all the
* required data structures for it. Please read the comment at the
* top of this file for high level overview.
*/
static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
{
struct cuse_conn *cc = fc_to_cc(fc), *pos;
struct cuse_init_out *arg = req->out.args[0].value;
struct page *page = req->pages[0];
struct cuse_devinfo devinfo = { };
struct device *dev;
struct cdev *cdev;
dev_t devt;
int rc, i;
if (req->out.h.error ||
arg->major != FUSE_KERNEL_VERSION || arg->minor < 11) {
goto err;
}
fc->minor = arg->minor;
fc->max_read = max_t(unsigned, arg->max_read, 4096);
fc->max_write = max_t(unsigned, arg->max_write, 4096);
/* parse init reply */
cc->unrestricted_ioctl = arg->flags & CUSE_UNRESTRICTED_IOCTL;
rc = cuse_parse_devinfo(page_address(page), req->out.args[1].size,
&devinfo);
if (rc)
goto err;
/* determine and reserve devt */
devt = MKDEV(arg->dev_major, arg->dev_minor);
if (!MAJOR(devt))
rc = alloc_chrdev_region(&devt, MINOR(devt), 1, devinfo.name);
else
rc = register_chrdev_region(devt, 1, devinfo.name);
if (rc) {
printk(KERN_ERR "CUSE: failed to register chrdev region\n");
goto err;
}
/* devt determined, create device */
rc = -ENOMEM;
dev = kzalloc(sizeof(*dev), GFP_KERNEL);
if (!dev)
goto err_region;
device_initialize(dev);
dev_set_uevent_suppress(dev, 1);
dev->class = cuse_class;
dev->devt = devt;
dev->release = cuse_gendev_release;
dev_set_drvdata(dev, cc);
dev_set_name(dev, "%s", devinfo.name);
mutex_lock(&cuse_lock);
/* make sure the device-name is unique */
for (i = 0; i < CUSE_CONNTBL_LEN; ++i) {
list_for_each_entry(pos, &cuse_conntbl[i], list)
if (!strcmp(dev_name(pos->dev), dev_name(dev)))
goto err_unlock;
}
rc = device_add(dev);
if (rc)
goto err_unlock;
/* register cdev */
rc = -ENOMEM;
cdev = cdev_alloc();
if (!cdev)
goto err_unlock;
cdev->owner = THIS_MODULE;
cdev->ops = &cuse_frontend_fops;
rc = cdev_add(cdev, devt, 1);
if (rc)
goto err_cdev;
cc->dev = dev;
cc->cdev = cdev;
/* make the device available */
list_add(&cc->list, cuse_conntbl_head(devt));
mutex_unlock(&cuse_lock);
/* announce device availability */
dev_set_uevent_suppress(dev, 0);
kobject_uevent(&dev->kobj, KOBJ_ADD);
out:
kfree(arg);
__free_page(page);
return;
err_cdev:
cdev_del(cdev);
err_unlock:
mutex_unlock(&cuse_lock);
put_device(dev);
err_region:
unregister_chrdev_region(devt, 1);
err:
fuse_abort_conn(fc);
goto out;
}
static int cuse_send_init(struct cuse_conn *cc)
{
int rc;
struct fuse_req *req;
struct page *page;
struct fuse_conn *fc = &cc->fc;
struct cuse_init_in *arg;
void *outarg;
BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);
req = fuse_get_req_for_background(fc, 1);
if (IS_ERR(req)) {
rc = PTR_ERR(req);
goto err;
}
rc = -ENOMEM;
page = alloc_page(GFP_KERNEL | __GFP_ZERO);
if (!page)
goto err_put_req;
outarg = kzalloc(sizeof(struct cuse_init_out), GFP_KERNEL);
if (!outarg)
goto err_free_page;
arg = &req->misc.cuse_init_in;
arg->major = FUSE_KERNEL_VERSION;
arg->minor = FUSE_KERNEL_MINOR_VERSION;
arg->flags |= CUSE_UNRESTRICTED_IOCTL;
req->in.h.opcode = CUSE_INIT;
req->in.numargs = 1;
req->in.args[0].size = sizeof(struct cuse_init_in);
req->in.args[0].value = arg;
req->out.numargs = 2;
req->out.args[0].size = sizeof(struct cuse_init_out);
req->out.args[0].value = outarg;
req->out.args[1].size = CUSE_INIT_INFO_MAX;
req->out.argvar = 1;
req->out.argpages = 1;
req->pages[0] = page;
req->page_descs[0].length = req->out.args[1].size;
req->num_pages = 1;
req->end = cuse_process_init_reply;
fuse_request_send_background(fc, req);
return 0;
err_free_page:
__free_page(page);
err_put_req:
fuse_put_request(fc, req);
err:
return rc;
}
static void cuse_fc_release(struct fuse_conn *fc)
{
struct cuse_conn *cc = fc_to_cc(fc);
kfree_rcu(cc, fc.rcu);
}
/**
* cuse_channel_open - open method for /dev/cuse
* @inode: inode for /dev/cuse
* @file: file struct being opened
*
* Userland CUSE server can create a CUSE device by opening /dev/cuse
* and replying to the initialization request kernel sends. This
* function is responsible for handling CUSE device initialization.
* Because the fd opened by this function is used during
* initialization, this function only creates cuse_conn and sends
* init. The rest is delegated to a kthread.
*
* RETURNS:
* 0 on success, -errno on failure.
*/
static int cuse_channel_open(struct inode *inode, struct file *file)
{
struct fuse_dev *fud;
struct cuse_conn *cc;
int rc;
/* set up cuse_conn */
cc = kzalloc(sizeof(*cc), GFP_KERNEL);
if (!cc)
return -ENOMEM;
fuse_conn_init(&cc->fc);
fud = fuse_dev_alloc(&cc->fc);
if (!fud) {
kfree(cc);
return -ENOMEM;
}
INIT_LIST_HEAD(&cc->list);
cc->fc.release = cuse_fc_release;
cc->fc.initialized = 1;
rc = cuse_send_init(cc);
if (rc) {
fuse_dev_free(fud);
return rc;
}
file->private_data = fud;
return 0;
}
/**
* cuse_channel_release - release method for /dev/cuse
* @inode: inode for /dev/cuse
* @file: file struct being closed
*
* Disconnect the channel, deregister CUSE device and initiate
* destruction by putting the default reference.
*
* RETURNS:
* 0 on success, -errno on failure.
*/
static int cuse_channel_release(struct inode *inode, struct file *file)
{
struct fuse_dev *fud = file->private_data;
struct cuse_conn *cc = fc_to_cc(fud->fc);
int rc;
/* remove from the conntbl, no more access from this point on */
mutex_lock(&cuse_lock);
list_del_init(&cc->list);
mutex_unlock(&cuse_lock);
/* remove device */
if (cc->dev)
device_unregister(cc->dev);
if (cc->cdev) {
unregister_chrdev_region(cc->cdev->dev, 1);
cdev_del(cc->cdev);
}
/* Base reference is now owned by "fud" */
fuse_conn_put(&cc->fc);
rc = fuse_dev_release(inode, file); /* puts the base reference */
return rc;
}
static struct file_operations cuse_channel_fops; /* initialized during init */
/**************************************************************************
* Misc stuff and module initializatiion
*
* CUSE exports the same set of attributes to sysfs as fusectl.
*/
static ssize_t cuse_class_waiting_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct cuse_conn *cc = dev_get_drvdata(dev);
return sprintf(buf, "%d\n", atomic_read(&cc->fc.num_waiting));
}
static DEVICE_ATTR(waiting, 0400, cuse_class_waiting_show, NULL);
static ssize_t cuse_class_abort_store(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
{
struct cuse_conn *cc = dev_get_drvdata(dev);
fuse_abort_conn(&cc->fc);
return count;
}
static DEVICE_ATTR(abort, 0200, NULL, cuse_class_abort_store);
static struct attribute *cuse_class_dev_attrs[] = {
&dev_attr_waiting.attr,
&dev_attr_abort.attr,
NULL,
};
ATTRIBUTE_GROUPS(cuse_class_dev);
static struct miscdevice cuse_miscdev = {
.minor = CUSE_MINOR,
.name = "cuse",
.fops = &cuse_channel_fops,
};
MODULE_ALIAS_MISCDEV(CUSE_MINOR);
MODULE_ALIAS("devname:cuse");
static int __init cuse_init(void)
{
int i, rc;
/* init conntbl */
for (i = 0; i < CUSE_CONNTBL_LEN; i++)
INIT_LIST_HEAD(&cuse_conntbl[i]);
/* inherit and extend fuse_dev_operations */
cuse_channel_fops = fuse_dev_operations;
cuse_channel_fops.owner = THIS_MODULE;
cuse_channel_fops.open = cuse_channel_open;
cuse_channel_fops.release = cuse_channel_release;
cuse_class = class_create(THIS_MODULE, "cuse");
if (IS_ERR(cuse_class))
return PTR_ERR(cuse_class);
cuse_class->dev_groups = cuse_class_dev_groups;
rc = misc_register(&cuse_miscdev);
if (rc) {
class_destroy(cuse_class);
return rc;
}
return 0;
}
static void __exit cuse_exit(void)
{
misc_deregister(&cuse_miscdev);
class_destroy(cuse_class);
}
module_init(cuse_init);
module_exit(cuse_exit);
MODULE_AUTHOR("Tejun Heo <tj@kernel.org>");
MODULE_DESCRIPTION("Character device in Userspace");
MODULE_LICENSE("GPL");