Commit message: aio: prevent double free in ioctx_alloc

ioctx_alloc() calls aio_setup_ring() to allocate a ring. If aio_setup_ring()
fails to do so it would call aio_free_ring() before returning, but
ioctx_alloc() would call aio_free_ring() again causing a double free of
the ring.

This is easily reproducible from userspace.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Benjamin LaHaise <bcrl@kvack.org>
CVE: CVE-2013-7348
CWE: CWE-399
Vulnerability description: Double free vulnerability in the ioctx_alloc function in fs/aio.c in the Linux kernel before 3.12.4 allows local users to cause a denial of service (system crash) or possibly have unspecified other impact via vectors involving an error condition in the aio_setup_ring function.

Project: linux
File: aio.c

SYSCALL_DEFINE1(io_destroy, aio_context_t, ctx)
{
	struct kioctx *ioctx = lookup_ioctx(ctx);
	if (likely(NULL != ioctx)) {
		kill_ioctx(current->mm, ioctx);
		percpu_ref_put(&ioctx->users);
		return 0;
	}
	pr_debug("EINVAL: io_destroy: invalid context id\n");
	return -EINVAL;
}

Project: linux
File: aio.c

SYSCALL_DEFINE2(io_setup, unsigned, nr_events, aio_context_t __user *, ctxp)
{
	struct kioctx *ioctx = NULL;
	unsigned long ctx;
	long ret;

	ret = get_user(ctx, ctxp);
	if (unlikely(ret))
		goto out;

	ret = -EINVAL;
	if (unlikely(ctx || nr_events == 0)) {
		pr_debug("EINVAL: io_setup: ctx %lu nr_events %u\n",
		         ctx, nr_events);
		goto out;
	}

	ioctx = ioctx_alloc(nr_events);
	ret = PTR_ERR(ioctx);
	if (!IS_ERR(ioctx)) {
		ret = put_user(ioctx->user_id, ctxp);
		if (ret)
			kill_ioctx(current->mm, ioctx);
		percpu_ref_put(&ioctx->users);
	}

out:
	return ret;
}

Project: linux
File: aio.c

SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
		struct io_event __user *, result)
{
	struct kioctx *ctx;
	struct kiocb *kiocb;
	u32 key;
	int ret;

	ret = get_user(key, &iocb->aio_key);
	if (unlikely(ret))
		return -EFAULT;

	ctx = lookup_ioctx(ctx_id);
	if (unlikely(!ctx))
		return -EINVAL;

	spin_lock_irq(&ctx->ctx_lock);

	kiocb = lookup_kiocb(ctx, iocb, key);
	if (kiocb)
		ret = kiocb_cancel(ctx, kiocb);
	else
		ret = -EINVAL;

	spin_unlock_irq(&ctx->ctx_lock);

	if (!ret) {
		/*
		 * The result argument is no longer used - the io_event is
		 * always delivered via the ring buffer. -EINPROGRESS indicates
		 * cancellation is progress:
		 */
		ret = -EINPROGRESS;
	}

	percpu_ref_put(&ctx->users);

	return ret;
}

Project: linux
File: aio.c

void aio_complete(struct kiocb *iocb, long res, long res2)
{
	struct kioctx	*ctx = iocb->ki_ctx;
	struct aio_ring	*ring;
	struct io_event	*ev_page, *event;
	unsigned long	flags;
	unsigned tail, pos;

	/*
	 * Special case handling for sync iocbs:
	 *  - events go directly into the iocb for fast handling
	 *  - the sync task with the iocb in its stack holds the single iocb
	 *    ref, no other paths have a way to get another ref
	 *  - the sync task helpfully left a reference to itself in the iocb
	 */
	if (is_sync_kiocb(iocb)) {
		iocb->ki_user_data = res;
		smp_wmb();
		iocb->ki_ctx = ERR_PTR(-EXDEV);
		wake_up_process(iocb->ki_obj.tsk);
		return;
	}

	if (iocb->ki_list.next) {
		unsigned long flags;

		spin_lock_irqsave(&ctx->ctx_lock, flags);
		list_del(&iocb->ki_list);
		spin_unlock_irqrestore(&ctx->ctx_lock, flags);
	}

	/*
	 * Add a completion event to the ring buffer. Must be done holding
	 * ctx->completion_lock to prevent other code from messing with the tail
	 * pointer since we might be called from irq context.
	 */
	spin_lock_irqsave(&ctx->completion_lock, flags);

	tail = ctx->tail;
	pos = tail + AIO_EVENTS_OFFSET;

	if (++tail >= ctx->nr_events)
		tail = 0;

	ev_page = kmap_atomic(ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE]);
	event = ev_page + pos % AIO_EVENTS_PER_PAGE;

	event->obj = (u64)(unsigned long)iocb->ki_obj.user;
	event->data = iocb->ki_user_data;
	event->res = res;
	event->res2 = res2;

	kunmap_atomic(ev_page);
	flush_dcache_page(ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE]);

	pr_debug("%p[%u]: %p: %p %Lx %lx %lx\n",
		 ctx, tail, iocb, iocb->ki_obj.user, iocb->ki_user_data,
		 res, res2);

	/* after flagging the request as done, we
	 * must never even look at it again
	 */
	smp_wmb();	/* make event visible before updating tail */

	ctx->tail = tail;

	ring = kmap_atomic(ctx->ring_pages[0]);
	ring->tail = tail;
	kunmap_atomic(ring);
	flush_dcache_page(ctx->ring_pages[0]);

	spin_unlock_irqrestore(&ctx->completion_lock, flags);

	pr_debug("added to ring %p at [%u]\n", iocb, tail);

	/*
	 * Check if the user asked us to deliver the result through an
	 * eventfd. The eventfd_signal() function is safe to be called
	 * from IRQ context.
	 */
	if (iocb->ki_eventfd != NULL)
		eventfd_signal(iocb->ki_eventfd, 1);

	/* everything turned out well, dispose of the aiocb. */
	kiocb_free(iocb);

	/*
	 * We have to order our ring_info tail store above and test
	 * of the wait list below outside the wait lock.  This is
	 * like in wake_up_bit() where clearing a bit has to be
	 * ordered with the unlocked test.
	 */
	smp_mb();

	if (waitqueue_active(&ctx->wait))
		wake_up(&ctx->wait);

	percpu_ref_put(&ctx->reqs);
}

Project: linux
File: aio.c

static void aio_free_ring(struct kioctx *ctx)
{
	int i;

	for (i = 0; i < ctx->nr_pages; i++) {
		pr_debug("pid(%d) [%d] page->count=%d\n", current->pid, i,
				page_count(ctx->ring_pages[i]));
		put_page(ctx->ring_pages[i]);
	}

	put_aio_ring_file(ctx);

	if (ctx->ring_pages && ctx->ring_pages != ctx->internal_pages)
		kfree(ctx->ring_pages);
}

Project: linux
File: aio.c

static int aio_migratepage(struct address_space *mapping, struct page *new,
			struct page *old, enum migrate_mode mode)
{
	struct kioctx *ctx;
	unsigned long flags;
	int rc;

	/* Writeback must be complete */
	BUG_ON(PageWriteback(old));
	put_page(old);

	rc = migrate_page_move_mapping(mapping, new, old, NULL, mode);
	if (rc != MIGRATEPAGE_SUCCESS) {
		get_page(old);
		return rc;
	}

	get_page(new);

	/* We can potentially race against kioctx teardown here.  Use the
	 * address_space's private data lock to protect the mapping's
	 * private_data.
	 */
	spin_lock(&mapping->private_lock);
	ctx = mapping->private_data;
	if (ctx) {
		pgoff_t idx;
		spin_lock_irqsave(&ctx->completion_lock, flags);
		migrate_page_copy(new, old);
		idx = old->index;
		if (idx < (pgoff_t)ctx->nr_pages)
			ctx->ring_pages[idx] = new;
		spin_unlock_irqrestore(&ctx->completion_lock, flags);
	} else
		rc = -EBUSY;
	spin_unlock(&mapping->private_lock);

	return rc;
}

Project: linux
File: aio.c

static ssize_t aio_run_iocb(struct kiocb *req, unsigned opcode,
			    char __user *buf, bool compat)
{
	struct file *file = req->ki_filp;
	ssize_t ret;
	unsigned long nr_segs;
	int rw;
	fmode_t mode;
	aio_rw_op *rw_op;
	struct iovec inline_vec, *iovec = &inline_vec;

	switch (opcode) {
	case IOCB_CMD_PREAD:
	case IOCB_CMD_PREADV:
		mode	= FMODE_READ;
		rw	= READ;
		rw_op	= file->f_op->aio_read;
		goto rw_common;

	case IOCB_CMD_PWRITE:
	case IOCB_CMD_PWRITEV:
		mode	= FMODE_WRITE;
		rw	= WRITE;
		rw_op	= file->f_op->aio_write;
		goto rw_common;
rw_common:
		if (unlikely(!(file->f_mode & mode)))
			return -EBADF;

		if (!rw_op)
			return -EINVAL;

		ret = (opcode == IOCB_CMD_PREADV ||
		       opcode == IOCB_CMD_PWRITEV)
			? aio_setup_vectored_rw(req, rw, buf, &nr_segs,
						&iovec, compat)
			: aio_setup_single_vector(req, rw, buf, &nr_segs,
						  iovec);
		if (ret)
			return ret;

		ret = rw_verify_area(rw, file, &req->ki_pos, req->ki_nbytes);
		if (ret < 0) {
			if (iovec != &inline_vec)
				kfree(iovec);
			return ret;
		}

		req->ki_nbytes = ret;

		/* XXX: move/kill - rw_verify_area()? */
		/* This matches the pread()/pwrite() logic */
		if (req->ki_pos < 0) {
			ret = -EINVAL;
			break;
		}

		if (rw == WRITE)
			file_start_write(file);

		ret = rw_op(req, iovec, nr_segs, req->ki_pos);

		if (rw == WRITE)
			file_end_write(file);
		break;

	case IOCB_CMD_FDSYNC:
		if (!file->f_op->aio_fsync)
			return -EINVAL;

		ret = file->f_op->aio_fsync(req, 1);
		break;

	case IOCB_CMD_FSYNC:
		if (!file->f_op->aio_fsync)
			return -EINVAL;

		ret = file->f_op->aio_fsync(req, 0);
		break;

	default:
		pr_debug("EINVAL: no operation provided\n");
		return -EINVAL;
	}

	if (iovec != &inline_vec)
		kfree(iovec);

	if (ret != -EIOCBQUEUED) {
		/*
		 * There's no easy way to restart the syscall since other AIO's
		 * may be already running. Just fail this IO with EINTR.
		 */
		if (unlikely(ret == -ERESTARTSYS || ret == -ERESTARTNOINTR ||
			     ret == -ERESTARTNOHAND ||
			     ret == -ERESTART_RESTARTBLOCK))
			ret = -EINTR;
		aio_complete(req, ret, 0);
	}

	return 0;
}

Project: linux
File: aio.c

static int aio_setup_ring(struct kioctx *ctx)
{
	struct aio_ring *ring;
	unsigned nr_events = ctx->max_reqs;
	struct mm_struct *mm = current->mm;
	unsigned long size, populate;
	int nr_pages;
	int i;
	struct file *file;

	/* Compensate for the ring buffer's head/tail overlap entry */
	nr_events += 2;	/* 1 is required, 2 for good luck */

	size = sizeof(struct aio_ring);
	size += sizeof(struct io_event) * nr_events;

	nr_pages = PFN_UP(size);
	if (nr_pages < 0)
		return -EINVAL;

	file = anon_inode_getfile_private("[aio]", &aio_ring_fops, ctx, O_RDWR);
	if (IS_ERR(file)) {
		ctx->aio_ring_file = NULL;
		return -EAGAIN;
	}

	file->f_inode->i_mapping->a_ops = &aio_ctx_aops;
	file->f_inode->i_mapping->private_data = ctx;
	file->f_inode->i_size = PAGE_SIZE * (loff_t)nr_pages;

	for (i = 0; i < nr_pages; i++) {
		struct page *page;
		page = find_or_create_page(file->f_inode->i_mapping,
					   i, GFP_HIGHUSER | __GFP_ZERO);
		if (!page)
			break;
		pr_debug("pid(%d) page[%d]->count=%d\n",
			 current->pid, i, page_count(page));
		SetPageUptodate(page);
		SetPageDirty(page);
		unlock_page(page);
	}
	ctx->aio_ring_file = file;
	nr_events = (PAGE_SIZE * nr_pages - sizeof(struct aio_ring))
			/ sizeof(struct io_event);

	ctx->ring_pages = ctx->internal_pages;
	if (nr_pages > AIO_RING_PAGES) {
		ctx->ring_pages = kcalloc(nr_pages, sizeof(struct page *),
					  GFP_KERNEL);
		if (!ctx->ring_pages)
			return -ENOMEM;
	}

	ctx->mmap_size = nr_pages * PAGE_SIZE;
	pr_debug("attempting mmap of %lu bytes\n", ctx->mmap_size);

	down_write(&mm->mmap_sem);
	ctx->mmap_base = do_mmap_pgoff(ctx->aio_ring_file, 0, ctx->mmap_size,
				       PROT_READ | PROT_WRITE,
				       MAP_SHARED | MAP_POPULATE, 0, &populate);
	if (IS_ERR((void *)ctx->mmap_base)) {
		up_write(&mm->mmap_sem);
		ctx->mmap_size = 0;
		aio_free_ring(ctx);
		return -EAGAIN;
	}

	pr_debug("mmap address: 0x%08lx\n", ctx->mmap_base);

	/* We must do this while still holding mmap_sem for write, as we
	 * need to be protected against userspace attempting to mremap()
	 * or munmap() the ring buffer.
	 */
	ctx->nr_pages = get_user_pages(current, mm, ctx->mmap_base, nr_pages,
				       1, 0, ctx->ring_pages, NULL);

	/* Dropping the reference here is safe as the page cache will hold
	 * onto the pages for us.  It is also required so that page migration
	 * can unmap the pages and get the right reference count.
	 */
	for (i = 0; i < ctx->nr_pages; i++)
		put_page(ctx->ring_pages[i]);

	up_write(&mm->mmap_sem);

	if (unlikely(ctx->nr_pages != nr_pages)) {
		aio_free_ring(ctx);
		return -EAGAIN;
	}

	ctx->user_id = ctx->mmap_base;
	ctx->nr_events = nr_events; /* trusted copy */

	ring = kmap_atomic(ctx->ring_pages[0]);
	ring->nr = nr_events;	/* user copy */
	ring->id = ~0U;
	ring->head = ring->tail = 0;
	ring->magic = AIO_RING_MAGIC;
	ring->compat_features = AIO_RING_COMPAT_FEATURES;
	ring->incompat_features = AIO_RING_INCOMPAT_FEATURES;
	ring->header_length = sizeof(struct aio_ring);
	kunmap_atomic(ring);
	flush_dcache_page(ctx->ring_pages[0]);

	return 0;
}

Project: linux
File: aio.c

static void free_ioctx_reqs(struct percpu_ref *ref)
{
	struct kioctx *ctx = container_of(ref, struct kioctx, reqs);

	INIT_WORK(&ctx->free_work, free_ioctx);
	schedule_work(&ctx->free_work);
}

Project: linux
File: aio.c

static void free_ioctx_users(struct percpu_ref *ref)
{
	struct kioctx *ctx = container_of(ref, struct kioctx, users);
	struct kiocb *req;

	spin_lock_irq(&ctx->ctx_lock);

	while (!list_empty(&ctx->active_reqs)) {
		req = list_first_entry(&ctx->active_reqs,
				       struct kiocb, ki_list);

		list_del_init(&req->ki_list);
		kiocb_cancel(ctx, req);
	}

	spin_unlock_irq(&ctx->ctx_lock);

	percpu_ref_kill(&ctx->reqs);
	percpu_ref_put(&ctx->reqs);
}

Project: linux
File: aio.c

static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
{
	unsigned i, new_nr;
	struct kioctx_table *table, *old;
	struct aio_ring *ring;

	spin_lock(&mm->ioctx_lock);
	rcu_read_lock();
	table = rcu_dereference(mm->ioctx_table);

	while (1) {
		if (table)
			for (i = 0; i < table->nr; i++)
				if (!table->table[i]) {
					ctx->id = i;
					table->table[i] = ctx;
					rcu_read_unlock();
					spin_unlock(&mm->ioctx_lock);

					ring = kmap_atomic(ctx->ring_pages[0]);
					ring->id = ctx->id;
					kunmap_atomic(ring);
					return 0;
				}

		new_nr = (table ? table->nr : 1) * 4;

		rcu_read_unlock();
		spin_unlock(&mm->ioctx_lock);

		table = kzalloc(sizeof(*table) + sizeof(struct kioctx *) *
				new_nr, GFP_KERNEL);
		if (!table)
			return -ENOMEM;

		table->nr = new_nr;

		spin_lock(&mm->ioctx_lock);
		rcu_read_lock();
		old = rcu_dereference(mm->ioctx_table);

		if (!old) {
			rcu_assign_pointer(mm->ioctx_table, table);
		} else if (table->nr > old->nr) {
			memcpy(table->table, old->table,
			       old->nr * sizeof(struct kioctx *));

			rcu_assign_pointer(mm->ioctx_table, table);
			kfree_rcu(old, rcu);
		} else {
			kfree(table);
			table = old;
		}
	}
}

Project: linux
File: aio.c

static void kill_ioctx(struct mm_struct *mm, struct kioctx *ctx)
{
	if (!atomic_xchg(&ctx->dead, 1)) {
		struct kioctx_table *table;

		spin_lock(&mm->ioctx_lock);
		rcu_read_lock();
		table = rcu_dereference(mm->ioctx_table);

		WARN_ON(ctx != table->table[ctx->id]);
		table->table[ctx->id] = NULL;
		rcu_read_unlock();
		spin_unlock(&mm->ioctx_lock);

		/* percpu_ref_kill() will do the necessary call_rcu() */
		wake_up_all(&ctx->wait);

		/*
		 * It'd be more correct to do this in free_ioctx(), after all
		 * the outstanding kiocbs have finished - but by then io_destroy
		 * has already returned, so io_setup() could potentially return
		 * -EAGAIN with no ioctxs actually in use (as far as userspace
		 *  could tell).
		 */
		aio_nr_sub(ctx->max_reqs);

		if (ctx->mmap_size)
			vm_munmap(ctx->mmap_base, ctx->mmap_size);

		percpu_ref_kill(&ctx->users);
	}
}

Project: linux
File: aio.c

static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb)
{
	kiocb_cancel_fn *old, *cancel;

	/*
	 * Don't want to set kiocb->ki_cancel = KIOCB_CANCELLED unless it
	 * actually has a cancel function, hence the cmpxchg()
	 */

	cancel = ACCESS_ONCE(kiocb->ki_cancel);
	do {
		if (!cancel || cancel == KIOCB_CANCELLED)
			return -EINVAL;

		old = cancel;
		cancel = cmpxchg(&kiocb->ki_cancel, old, KIOCB_CANCELLED);
	} while (cancel != old);

	return cancel(kiocb);
}