lguest: dereferencing freed mem in add_eventfd()

[safe/jmp/linux-2.6] / drivers / lguest / lguest_user.c

/*P:200 This contains all the /dev/lguest code, whereby the userspace launcher
 * controls and communicates with the Guest.  For example, the first write will
 * tell us the Guest's memory layout, pagetable, entry point and kernel address
 * offset.  A read will run the Guest until something happens, such as a signal
 * or the Guest doing a NOTIFY out to the Launcher. :*/
#include <linux/uaccess.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include <linux/eventfd.h>
#include <linux/file.h>
#include "lg.h"

bool send_notify_to_eventfd(struct lg_cpu *cpu)
{
        unsigned int i;
        struct lg_eventfd_map *map;

        /* lg->eventfds is RCU-protected */
        rcu_read_lock();
        map = rcu_dereference(cpu->lg->eventfds);
        for (i = 0; i < map->num; i++) {
                if (map->map[i].addr == cpu->pending_notify) {
                        eventfd_signal(map->map[i].event, 1);
                        cpu->pending_notify = 0;
                        break;
                }
        }
        rcu_read_unlock();
        return cpu->pending_notify == 0;
}

static int add_eventfd(struct lguest *lg, unsigned long addr, int fd)
{
        struct lg_eventfd_map *new, *old = lg->eventfds;

        if (!addr)
                return -EINVAL;

        /* Replace the old array with the new one, carefully: others can
         * be accessing it at the same time */
        new = kmalloc(sizeof(*new) + sizeof(new->map[0]) * (old->num + 1),
                      GFP_KERNEL);
        if (!new)
                return -ENOMEM;

        /* First make identical copy. */
        memcpy(new->map, old->map, sizeof(old->map[0]) * old->num);
        new->num = old->num;

        /* Now append new entry. */
        new->map[new->num].addr = addr;
        new->map[new->num].event = eventfd_ctx_fdget(fd);
        if (IS_ERR(new->map[new->num].event)) {
                int err =  PTR_ERR(new->map[new->num].event);
                kfree(new);
                return err;
        }
        new->num++;

        /* Now put new one in place. */
        rcu_assign_pointer(lg->eventfds, new);

        /* We're not in a big hurry.  Wait until noone's looking at old
         * version, then delete it. */
        synchronize_rcu();
        kfree(old);

        return 0;
}

static int attach_eventfd(struct lguest *lg, const unsigned long __user *input)
{
        unsigned long addr, fd;
        int err;

        if (get_user(addr, input) != 0)
                return -EFAULT;
        input++;
        if (get_user(fd, input) != 0)
                return -EFAULT;

        mutex_lock(&lguest_lock);
        err = add_eventfd(lg, addr, fd);
        mutex_unlock(&lguest_lock);

        return err;
}

/*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
 * number to /dev/lguest. */
static int user_send_irq(struct lg_cpu *cpu, const unsigned long __user *input)
{
        unsigned long irq;

        if (get_user(irq, input) != 0)
                return -EFAULT;
        if (irq >= LGUEST_IRQS)
                return -EINVAL;

        set_interrupt(cpu, irq);
        return 0;
}

/*L:040 Once our Guest is initialized, the Launcher makes it run by reading
 * from /dev/lguest. */
static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
{
        struct lguest *lg = file->private_data;
        struct lg_cpu *cpu;
        unsigned int cpu_id = *o;

        /* You must write LHREQ_INITIALIZE first! */
        if (!lg)
                return -EINVAL;

        /* Watch out for arbitrary vcpu indexes! */
        if (cpu_id >= lg->nr_cpus)
                return -EINVAL;

        cpu = &lg->cpus[cpu_id];

        /* If you're not the task which owns the Guest, go away. */
        if (current != cpu->tsk)
                return -EPERM;

        /* If the Guest is already dead, we indicate why */
        if (lg->dead) {
                size_t len;

                /* lg->dead either contains an error code, or a string. */
                if (IS_ERR(lg->dead))
                        return PTR_ERR(lg->dead);

                /* We can only return as much as the buffer they read with. */
                len = min(size, strlen(lg->dead)+1);
                if (copy_to_user(user, lg->dead, len) != 0)
                        return -EFAULT;
                return len;
        }

        /* If we returned from read() last time because the Guest sent I/O,
         * clear the flag. */
        if (cpu->pending_notify)
                cpu->pending_notify = 0;

        /* Run the Guest until something interesting happens. */
        return run_guest(cpu, (unsigned long __user *)user);
}

/*L:025 This actually initializes a CPU.  For the moment, a Guest is only
 * uniprocessor, so "id" is always 0. */
static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
{
        /* We have a limited number the number of CPUs in the lguest struct. */
        if (id >= ARRAY_SIZE(cpu->lg->cpus))
                return -EINVAL;

        /* Set up this CPU's id, and pointer back to the lguest struct. */
        cpu->id = id;
        cpu->lg = container_of((cpu - id), struct lguest, cpus[0]);
        cpu->lg->nr_cpus++;

        /* Each CPU has a timer it can set. */
        init_clockdev(cpu);

        /* We need a complete page for the Guest registers: they are accessible
         * to the Guest and we can only grant it access to whole pages. */
        cpu->regs_page = get_zeroed_page(GFP_KERNEL);
        if (!cpu->regs_page)
                return -ENOMEM;

        /* We actually put the registers at the bottom of the page. */
        cpu->regs = (void *)cpu->regs_page + PAGE_SIZE - sizeof(*cpu->regs);

        /* Now we initialize the Guest's registers, handing it the start
         * address. */
        lguest_arch_setup_regs(cpu, start_ip);

        /* We keep a pointer to the Launcher task (ie. current task) for when
         * other Guests want to wake this one (eg. console input). */
        cpu->tsk = current;

        /* We need to keep a pointer to the Launcher's memory map, because if
         * the Launcher dies we need to clean it up.  If we don't keep a
         * reference, it is destroyed before close() is called. */
        cpu->mm = get_task_mm(cpu->tsk);

        /* We remember which CPU's pages this Guest used last, for optimization
         * when the same Guest runs on the same CPU twice. */
        cpu->last_pages = NULL;

        /* No error == success. */
        return 0;
}

/*L:020 The initialization write supplies 3 pointer sized (32 or 64 bit)
 * values (in addition to the LHREQ_INITIALIZE value).  These are:
 *
 * base: The start of the Guest-physical memory inside the Launcher memory.
 *
 * pfnlimit: The highest (Guest-physical) page number the Guest should be
 * allowed to access.  The Guest memory lives inside the Launcher, so it sets
 * this to ensure the Guest can only reach its own memory.
 *
 * start: The first instruction to execute ("eip" in x86-speak).
 */
static int initialize(struct file *file, const unsigned long __user *input)
{
        /* "struct lguest" contains everything we (the Host) know about a
         * Guest. */
        struct lguest *lg;
        int err;
        unsigned long args[3];

        /* We grab the Big Lguest lock, which protects against multiple
         * simultaneous initializations. */
        mutex_lock(&lguest_lock);
        /* You can't initialize twice!  Close the device and start again... */
        if (file->private_data) {
                err = -EBUSY;
                goto unlock;
        }

        if (copy_from_user(args, input, sizeof(args)) != 0) {
                err = -EFAULT;
                goto unlock;
        }

        lg = kzalloc(sizeof(*lg), GFP_KERNEL);
        if (!lg) {
                err = -ENOMEM;
                goto unlock;
        }

        lg->eventfds = kmalloc(sizeof(*lg->eventfds), GFP_KERNEL);
        if (!lg->eventfds) {
                err = -ENOMEM;
                goto free_lg;
        }
        lg->eventfds->num = 0;

        /* Populate the easy fields of our "struct lguest" */
        lg->mem_base = (void __user *)args[0];
        lg->pfn_limit = args[1];

        /* This is the first cpu (cpu 0) and it will start booting at args[2] */
        err = lg_cpu_start(&lg->cpus[0], 0, args[2]);
        if (err)
                goto free_eventfds;

        /* Initialize the Guest's shadow page tables, using the toplevel
         * address the Launcher gave us.  This allocates memory, so can fail. */
        err = init_guest_pagetable(lg);
        if (err)
                goto free_regs;

        /* We keep our "struct lguest" in the file's private_data. */
        file->private_data = lg;

        mutex_unlock(&lguest_lock);

        /* And because this is a write() call, we return the length used. */
        return sizeof(args);

free_regs:
        /* FIXME: This should be in free_vcpu */
        free_page(lg->cpus[0].regs_page);
free_eventfds:
        kfree(lg->eventfds);
free_lg:
        kfree(lg);
unlock:
        mutex_unlock(&lguest_lock);
        return err;
}

/*L:010 The first operation the Launcher does must be a write.  All writes
 * start with an unsigned long number: for the first write this must be
 * LHREQ_INITIALIZE to set up the Guest.  After that the Launcher can use
 * writes of other values to send interrupts.
 *
 * Note that we overload the "offset" in the /dev/lguest file to indicate what
 * CPU number we're dealing with.  Currently this is always 0, since we only
 * support uniprocessor Guests, but you can see the beginnings of SMP support
 * here. */
static ssize_t write(struct file *file, const char __user *in,
                     size_t size, loff_t *off)
{
        /* Once the Guest is initialized, we hold the "struct lguest" in the
         * file private data. */
        struct lguest *lg = file->private_data;
        const unsigned long __user *input = (const unsigned long __user *)in;
        unsigned long req;
        struct lg_cpu *uninitialized_var(cpu);
        unsigned int cpu_id = *off;

        /* The first value tells us what this request is. */
        if (get_user(req, input) != 0)
                return -EFAULT;
        input++;

        /* If you haven't initialized, you must do that first. */
        if (req != LHREQ_INITIALIZE) {
                if (!lg || (cpu_id >= lg->nr_cpus))
                        return -EINVAL;
                cpu = &lg->cpus[cpu_id];

                /* Once the Guest is dead, you can only read() why it died. */
                if (lg->dead)
                        return -ENOENT;
        }

        switch (req) {
        case LHREQ_INITIALIZE:
                return initialize(file, input);
        case LHREQ_IRQ:
                return user_send_irq(cpu, input);
        case LHREQ_EVENTFD:
                return attach_eventfd(lg, input);
        default:
                return -EINVAL;
        }
}

/*L:060 The final piece of interface code is the close() routine.  It reverses
 * everything done in initialize().  This is usually called because the
 * Launcher exited.
 *
 * Note that the close routine returns 0 or a negative error number: it can't
 * really fail, but it can whine.  I blame Sun for this wart, and K&R C for
 * letting them do it. :*/
static int close(struct inode *inode, struct file *file)
{
        struct lguest *lg = file->private_data;
        unsigned int i;

        /* If we never successfully initialized, there's nothing to clean up */
        if (!lg)
                return 0;

        /* We need the big lock, to protect from inter-guest I/O and other
         * Launchers initializing guests. */
        mutex_lock(&lguest_lock);

        /* Free up the shadow page tables for the Guest. */
        free_guest_pagetable(lg);

        for (i = 0; i < lg->nr_cpus; i++) {
                /* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
                hrtimer_cancel(&lg->cpus[i].hrt);
                /* We can free up the register page we allocated. */
                free_page(lg->cpus[i].regs_page);
                /* Now all the memory cleanups are done, it's safe to release
                 * the Launcher's memory management structure. */
                mmput(lg->cpus[i].mm);
        }

        /* Release any eventfds they registered. */
        for (i = 0; i < lg->eventfds->num; i++)
                eventfd_ctx_put(lg->eventfds->map[i].event);
        kfree(lg->eventfds);

        /* If lg->dead doesn't contain an error code it will be NULL or a
         * kmalloc()ed string, either of which is ok to hand to kfree(). */
        if (!IS_ERR(lg->dead))
                kfree(lg->dead);
        /* Free the memory allocated to the lguest_struct */
        kfree(lg);
        /* Release lock and exit. */
        mutex_unlock(&lguest_lock);

        return 0;
}

/*L:000
 * Welcome to our journey through the Launcher!
 *
 * The Launcher is the Host userspace program which sets up, runs and services
 * the Guest.  In fact, many comments in the Drivers which refer to "the Host"
 * doing things are inaccurate: the Launcher does all the device handling for
 * the Guest, but the Guest can't know that.
 *
 * Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
 * shall see more of that later.
 *
 * We begin our understanding with the Host kernel interface which the Launcher
 * uses: reading and writing a character device called /dev/lguest.  All the
 * work happens in the read(), write() and close() routines: */
static struct file_operations lguest_fops = {
        .owner   = THIS_MODULE,
        .release = close,
        .write   = write,
        .read    = read,
};

/* This is a textbook example of a "misc" character device.  Populate a "struct
 * miscdevice" and register it with misc_register(). */
static struct miscdevice lguest_dev = {
        .minor  = MISC_DYNAMIC_MINOR,
        .name   = "lguest",
        .fops   = &lguest_fops,
};

int __init lguest_device_init(void)
{
        return misc_register(&lguest_dev);
}

void __exit lguest_device_remove(void)
{
        misc_deregister(&lguest_dev);
}