linux-6.14.4/io_uring/rsrc.c

// SPDX-License-Identifier: GPL-2.0
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/nospec.h>
#include <linux/hugetlb.h>
#include <linux/compat.h>
#include <linux/io_uring.h>

#include <uapi/linux/io_uring.h>

#include "io_uring.h"
#include "openclose.h"
#include "rsrc.h"
#include "memmap.h"
#include "register.h"

struct io_rsrc_update {
	struct file			*file;
	u64				arg;
	u32				nr_args;
	u32				offset;
};

static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
			struct iovec *iov, struct page **last_hpage);

/* only define max */
#define IORING_MAX_FIXED_FILES	(1U << 20)
#define IORING_MAX_REG_BUFFERS	(1U << 14)

int __io_account_mem(struct user_struct *user, unsigned long nr_pages)
{
	unsigned long page_limit, cur_pages, new_pages;

	if (!nr_pages)
		return 0;

	/* Don't allow more pages than we can safely lock */
	page_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;

	cur_pages = atomic_long_read(&user->locked_vm);
	do {
		new_pages = cur_pages + nr_pages;
		if (new_pages > page_limit)
			return -ENOMEM;
	} while (!atomic_long_try_cmpxchg(&user->locked_vm,
					  &cur_pages, new_pages));
	return 0;
}

static void io_unaccount_mem(struct io_ring_ctx *ctx, unsigned long nr_pages)
{
	if (ctx->user)
		__io_unaccount_mem(ctx->user, nr_pages);

	if (ctx->mm_account)
		atomic64_sub(nr_pages, &ctx->mm_account->pinned_vm);
}

static int io_account_mem(struct io_ring_ctx *ctx, unsigned long nr_pages)
{
	int ret;

	if (ctx->user) {
		ret = __io_account_mem(ctx->user, nr_pages);
		if (ret)
			return ret;
	}

	if (ctx->mm_account)
		atomic64_add(nr_pages, &ctx->mm_account->pinned_vm);

	return 0;
}

static int io_buffer_validate(struct iovec *iov)
{
	unsigned long tmp, acct_len = iov->iov_len + (PAGE_SIZE - 1);

	/*
	 * Don't impose further limits on the size and buffer
	 * constraints here, we'll -EINVAL later when IO is
	 * submitted if they are wrong.
	 */
	if (!iov->iov_base)
		return iov->iov_len ? -EFAULT : 0;
	if (!iov->iov_len)
		return -EFAULT;

	/* arbitrary limit, but we need something */
	if (iov->iov_len > SZ_1G)
		return -EFAULT;

	if (check_add_overflow((unsigned long)iov->iov_base, acct_len, &tmp))
		return -EOVERFLOW;

	return 0;
}

static void io_buffer_unmap(struct io_ring_ctx *ctx, struct io_rsrc_node *node)
{
	unsigned int i;

	if (node->buf) {
		struct io_mapped_ubuf *imu = node->buf;

		if (!refcount_dec_and_test(&imu->refs))
			return;
		for (i = 0; i < imu->nr_bvecs; i++)
			unpin_user_page(imu->bvec[i].bv_page);
		if (imu->acct_pages)
			io_unaccount_mem(ctx, imu->acct_pages);
		kvfree(imu);
	}
}

struct io_rsrc_node *io_rsrc_node_alloc(int type)
{
	struct io_rsrc_node *node;

	node = kzalloc(sizeof(*node), GFP_KERNEL);
	if (node) {
		node->type = type;
		node->refs = 1;
	}
	return node;
}

static void io_clear_table_tags(struct io_rsrc_data *data)
{
	int i;

	for (i = 0; i < data->nr; i++) {
		struct io_rsrc_node *node = data->nodes[i];

		if (node)
			node->tag = 0;
	}
}

__cold void io_rsrc_data_free(struct io_ring_ctx *ctx, struct io_rsrc_data *data)
{
	if (!data->nr)
		return;
	while (data->nr--) {
		if (data->nodes[data->nr])
			io_put_rsrc_node(ctx, data->nodes[data->nr]);
	}
	kvfree(data->nodes);
	data->nodes = NULL;
	data->nr = 0;
}

__cold int io_rsrc_data_alloc(struct io_rsrc_data *data, unsigned nr)
{
	data->nodes = kvmalloc_array(nr, sizeof(struct io_rsrc_node *),
					GFP_KERNEL_ACCOUNT | __GFP_ZERO);
	if (data->nodes) {
		data->nr = nr;
		return 0;
	}
	return -ENOMEM;
}

static int __io_sqe_files_update(struct io_ring_ctx *ctx,
				 struct io_uring_rsrc_update2 *up,
				 unsigned nr_args)
{
	u64 __user *tags = u64_to_user_ptr(up->tags);
	__s32 __user *fds = u64_to_user_ptr(up->data);
	int fd, i, err = 0;
	unsigned int done;

	if (!ctx->file_table.data.nr)
		return -ENXIO;
	if (up->offset + nr_args > ctx->file_table.data.nr)
		return -EINVAL;

	for (done = 0; done < nr_args; done++) {
		u64 tag = 0;

		if ((tags && copy_from_user(&tag, &tags[done], sizeof(tag))) ||
		    copy_from_user(&fd, &fds[done], sizeof(fd))) {
			err = -EFAULT;
			break;
		}
		if ((fd == IORING_REGISTER_FILES_SKIP || fd == -1) && tag) {
			err = -EINVAL;
			break;
		}
		if (fd == IORING_REGISTER_FILES_SKIP)
			continue;

		i = up->offset + done;
		if (io_reset_rsrc_node(ctx, &ctx->file_table.data, i))
			io_file_bitmap_clear(&ctx->file_table, i);

		if (fd != -1) {
			struct file *file = fget(fd);
			struct io_rsrc_node *node;

			if (!file) {
				err = -EBADF;
				break;
			}
			/*
			 * Don't allow io_uring instances to be registered.
			 */
			if (io_is_uring_fops(file)) {
				fput(file);
				err = -EBADF;
				break;
			}
			node = io_rsrc_node_alloc(IORING_RSRC_FILE);
			if (!node) {
				err = -ENOMEM;
				fput(file);
				break;
			}
			ctx->file_table.data.nodes[i] = node;
			if (tag)
				node->tag = tag;
			io_fixed_file_set(node, file);
			io_file_bitmap_set(&ctx->file_table, i);
		}
	}
	return done ? done : err;
}

static int __io_sqe_buffers_update(struct io_ring_ctx *ctx,
				   struct io_uring_rsrc_update2 *up,
				   unsigned int nr_args)
{
	u64 __user *tags = u64_to_user_ptr(up->tags);
	struct iovec fast_iov, *iov;
	struct page *last_hpage = NULL;
	struct iovec __user *uvec;
	u64 user_data = up->data;
	__u32 done;
	int i, err;

	if (!ctx->buf_table.nr)
		return -ENXIO;
	if (up->offset + nr_args > ctx->buf_table.nr)
		return -EINVAL;

	for (done = 0; done < nr_args; done++) {
		struct io_rsrc_node *node;
		u64 tag = 0;

		uvec = u64_to_user_ptr(user_data);
		iov = iovec_from_user(uvec, 1, 1, &fast_iov, ctx->compat);
		if (IS_ERR(iov)) {
			err = PTR_ERR(iov);
			break;
		}
		if (tags && copy_from_user(&tag, &tags[done], sizeof(tag))) {
			err = -EFAULT;
			break;
		}
		err = io_buffer_validate(iov);
		if (err)
			break;
		node = io_sqe_buffer_register(ctx, iov, &last_hpage);
		if (IS_ERR(node)) {
			err = PTR_ERR(node);
			break;
		}
		if (tag) {
			if (!node) {
				err = -EINVAL;
				break;
			}
			node->tag = tag;
		}
		i = array_index_nospec(up->offset + done, ctx->buf_table.nr);
		io_reset_rsrc_node(ctx, &ctx->buf_table, i);
		ctx->buf_table.nodes[i] = node;
		if (ctx->compat)
			user_data += sizeof(struct compat_iovec);
		else
			user_data += sizeof(struct iovec);
	}
	return done ? done : err;
}

static int __io_register_rsrc_update(struct io_ring_ctx *ctx, unsigned type,
				     struct io_uring_rsrc_update2 *up,
				     unsigned nr_args)
{
	__u32 tmp;

	lockdep_assert_held(&ctx->uring_lock);

	if (check_add_overflow(up->offset, nr_args, &tmp))
		return -EOVERFLOW;

	switch (type) {
	case IORING_RSRC_FILE:
		return __io_sqe_files_update(ctx, up, nr_args);
	case IORING_RSRC_BUFFER:
		return __io_sqe_buffers_update(ctx, up, nr_args);
	}
	return -EINVAL;
}

int io_register_files_update(struct io_ring_ctx *ctx, void __user *arg,
			     unsigned nr_args)
{
	struct io_uring_rsrc_update2 up;

	if (!nr_args)
		return -EINVAL;
	memset(&up, 0, sizeof(up));
	if (copy_from_user(&up, arg, sizeof(struct io_uring_rsrc_update)))
		return -EFAULT;
	if (up.resv || up.resv2)
		return -EINVAL;
	return __io_register_rsrc_update(ctx, IORING_RSRC_FILE, &up, nr_args);
}

int io_register_rsrc_update(struct io_ring_ctx *ctx, void __user *arg,
			    unsigned size, unsigned type)
{
	struct io_uring_rsrc_update2 up;

	if (size != sizeof(up))
		return -EINVAL;
	if (copy_from_user(&up, arg, sizeof(up)))
		return -EFAULT;
	if (!up.nr || up.resv || up.resv2)
		return -EINVAL;
	return __io_register_rsrc_update(ctx, type, &up, up.nr);
}

__cold int io_register_rsrc(struct io_ring_ctx *ctx, void __user *arg,
			    unsigned int size, unsigned int type)
{
	struct io_uring_rsrc_register rr;

	/* keep it extendible */
	if (size != sizeof(rr))
		return -EINVAL;

	memset(&rr, 0, sizeof(rr));
	if (copy_from_user(&rr, arg, size))
		return -EFAULT;
	if (!rr.nr || rr.resv2)
		return -EINVAL;
	if (rr.flags & ~IORING_RSRC_REGISTER_SPARSE)
		return -EINVAL;

	switch (type) {
	case IORING_RSRC_FILE:
		if (rr.flags & IORING_RSRC_REGISTER_SPARSE && rr.data)
			break;
		return io_sqe_files_register(ctx, u64_to_user_ptr(rr.data),
					     rr.nr, u64_to_user_ptr(rr.tags));
	case IORING_RSRC_BUFFER:
		if (rr.flags & IORING_RSRC_REGISTER_SPARSE && rr.data)
			break;
		return io_sqe_buffers_register(ctx, u64_to_user_ptr(rr.data),
					       rr.nr, u64_to_user_ptr(rr.tags));
	}
	return -EINVAL;
}

int io_files_update_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
{
	struct io_rsrc_update *up = io_kiocb_to_cmd(req, struct io_rsrc_update);

	if (unlikely(req->flags & (REQ_F_FIXED_FILE | REQ_F_BUFFER_SELECT)))
		return -EINVAL;
	if (sqe->rw_flags || sqe->splice_fd_in)
		return -EINVAL;

	up->offset = READ_ONCE(sqe->off);
	up->nr_args = READ_ONCE(sqe->len);
	if (!up->nr_args)
		return -EINVAL;
	up->arg = READ_ONCE(sqe->addr);
	return 0;
}

static int io_files_update_with_index_alloc(struct io_kiocb *req,
					    unsigned int issue_flags)
{
	struct io_rsrc_update *up = io_kiocb_to_cmd(req, struct io_rsrc_update);
	__s32 __user *fds = u64_to_user_ptr(up->arg);
	unsigned int done;
	struct file *file;
	int ret, fd;

	if (!req->ctx->file_table.data.nr)
		return -ENXIO;

	for (done = 0; done < up->nr_args; done++) {
		if (copy_from_user(&fd, &fds[done], sizeof(fd))) {
			ret = -EFAULT;
			break;
		}

		file = fget(fd);
		if (!file) {
			ret = -EBADF;
			break;
		}
		ret = io_fixed_fd_install(req, issue_flags, file,
					  IORING_FILE_INDEX_ALLOC);
		if (ret < 0)
			break;
		if (copy_to_user(&fds[done], &ret, sizeof(ret))) {
			__io_close_fixed(req->ctx, issue_flags, ret);
			ret = -EFAULT;
			break;
		}
	}

	if (done)
		return done;
	return ret;
}

int io_files_update(struct io_kiocb *req, unsigned int issue_flags)
{
	struct io_rsrc_update *up = io_kiocb_to_cmd(req, struct io_rsrc_update);
	struct io_ring_ctx *ctx = req->ctx;
	struct io_uring_rsrc_update2 up2;
	int ret;

	up2.offset = up->offset;
	up2.data = up->arg;
	up2.nr = 0;
	up2.tags = 0;
	up2.resv = 0;
	up2.resv2 = 0;

	if (up->offset == IORING_FILE_INDEX_ALLOC) {
		ret = io_files_update_with_index_alloc(req, issue_flags);
	} else {
		io_ring_submit_lock(ctx, issue_flags);
		ret = __io_register_rsrc_update(ctx, IORING_RSRC_FILE,
						&up2, up->nr_args);
		io_ring_submit_unlock(ctx, issue_flags);
	}

	if (ret < 0)
		req_set_fail(req);
	io_req_set_res(req, ret, 0);
	return IOU_OK;
}

void io_free_rsrc_node(struct io_ring_ctx *ctx, struct io_rsrc_node *node)
{
	if (node->tag)
		io_post_aux_cqe(ctx, node->tag, 0, 0);

	switch (node->type) {
	case IORING_RSRC_FILE:
		if (io_slot_file(node))
			fput(io_slot_file(node));
		break;
	case IORING_RSRC_BUFFER:
		if (node->buf)
			io_buffer_unmap(ctx, node);
		break;
	default:
		WARN_ON_ONCE(1);
		break;
	}

	kfree(node);
}

int io_sqe_files_unregister(struct io_ring_ctx *ctx)
{
	if (!ctx->file_table.data.nr)
		return -ENXIO;

	io_free_file_tables(ctx, &ctx->file_table);
	io_file_table_set_alloc_range(ctx, 0, 0);
	return 0;
}

int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
			  unsigned nr_args, u64 __user *tags)
{
	__s32 __user *fds = (__s32 __user *) arg;
	struct file *file;
	int fd, ret;
	unsigned i;

	if (ctx->file_table.data.nr)
		return -EBUSY;
	if (!nr_args)
		return -EINVAL;
	if (nr_args > IORING_MAX_FIXED_FILES)
		return -EMFILE;
	if (nr_args > rlimit(RLIMIT_NOFILE))
		return -EMFILE;
	if (!io_alloc_file_tables(ctx, &ctx->file_table, nr_args))
		return -ENOMEM;

	for (i = 0; i < nr_args; i++) {
		struct io_rsrc_node *node;
		u64 tag = 0;

		ret = -EFAULT;
		if (tags && copy_from_user(&tag, &tags[i], sizeof(tag)))
			goto fail;
		if (fds && copy_from_user(&fd, &fds[i], sizeof(fd)))
			goto fail;
		/* allow sparse sets */
		if (!fds || fd == -1) {
			ret = -EINVAL;
			if (tag)
				goto fail;
			continue;
		}

		file = fget(fd);
		ret = -EBADF;
		if (unlikely(!file))
			goto fail;

		/*
		 * Don't allow io_uring instances to be registered.
		 */
		if (io_is_uring_fops(file)) {
			fput(file);
			goto fail;
		}
		ret = -ENOMEM;
		node = io_rsrc_node_alloc(IORING_RSRC_FILE);
		if (!node) {
			fput(file);
			goto fail;
		}
		if (tag)
			node->tag = tag;
		ctx->file_table.data.nodes[i] = node;
		io_fixed_file_set(node, file);
		io_file_bitmap_set(&ctx->file_table, i);
	}

	/* default it to the whole table */
	io_file_table_set_alloc_range(ctx, 0, ctx->file_table.data.nr);
	return 0;
fail:
	io_clear_table_tags(&ctx->file_table.data);
	io_sqe_files_unregister(ctx);
	return ret;
}

int io_sqe_buffers_unregister(struct io_ring_ctx *ctx)
{
	if (!ctx->buf_table.nr)
		return -ENXIO;
	io_rsrc_data_free(ctx, &ctx->buf_table);
	return 0;
}

/*
 * Not super efficient, but this is just a registration time. And we do cache
 * the last compound head, so generally we'll only do a full search if we don't
 * match that one.
 *
 * We check if the given compound head page has already been accounted, to
 * avoid double accounting it. This allows us to account the full size of the
 * page, not just the constituent pages of a huge page.
 */
static bool headpage_already_acct(struct io_ring_ctx *ctx, struct page **pages,
				  int nr_pages, struct page *hpage)
{
	int i, j;

	/* check current page array */
	for (i = 0; i < nr_pages; i++) {
		if (!PageCompound(pages[i]))
			continue;
		if (compound_head(pages[i]) == hpage)
			return true;
	}

	/* check previously registered pages */
	for (i = 0; i < ctx->buf_table.nr; i++) {
		struct io_rsrc_node *node = ctx->buf_table.nodes[i];
		struct io_mapped_ubuf *imu;

		if (!node)
			continue;
		imu = node->buf;
		for (j = 0; j < imu->nr_bvecs; j++) {
			if (!PageCompound(imu->bvec[j].bv_page))
				continue;
			if (compound_head(imu->bvec[j].bv_page) == hpage)
				return true;
		}
	}

	return false;
}

static int io_buffer_account_pin(struct io_ring_ctx *ctx, struct page **pages,
				 int nr_pages, struct io_mapped_ubuf *imu,
				 struct page **last_hpage)
{
	int i, ret;

	imu->acct_pages = 0;
	for (i = 0; i < nr_pages; i++) {
		if (!PageCompound(pages[i])) {
			imu->acct_pages++;
		} else {
			struct page *hpage;

			hpage = compound_head(pages[i]);
			if (hpage == *last_hpage)
				continue;
			*last_hpage = hpage;
			if (headpage_already_acct(ctx, pages, i, hpage))
				continue;
			imu->acct_pages += page_size(hpage) >> PAGE_SHIFT;
		}
	}

	if (!imu->acct_pages)
		return 0;

	ret = io_account_mem(ctx, imu->acct_pages);
	if (ret)
		imu->acct_pages = 0;
	return ret;
}

static bool io_coalesce_buffer(struct page ***pages, int *nr_pages,
				struct io_imu_folio_data *data)
{
	struct page **page_array = *pages, **new_array = NULL;
	int nr_pages_left = *nr_pages, i, j;
	int nr_folios = data->nr_folios;

	/* Store head pages only*/
	new_array = kvmalloc_array(nr_folios, sizeof(struct page *),
					GFP_KERNEL);
	if (!new_array)
		return false;

	new_array[0] = compound_head(page_array[0]);
	/*
	 * The pages are bound to the folio, it doesn't
	 * actually unpin them but drops all but one reference,
	 * which is usually put down by io_buffer_unmap().
	 * Note, needs a better helper.
	 */
	if (data->nr_pages_head > 1)
		unpin_user_pages(&page_array[1], data->nr_pages_head - 1);

	j = data->nr_pages_head;
	nr_pages_left -= data->nr_pages_head;
	for (i = 1; i < nr_folios; i++) {
		unsigned int nr_unpin;

		new_array[i] = page_array[j];
		nr_unpin = min_t(unsigned int, nr_pages_left - 1,
					data->nr_pages_mid - 1);
		if (nr_unpin)
			unpin_user_pages(&page_array[j+1], nr_unpin);
		j += data->nr_pages_mid;
		nr_pages_left -= data->nr_pages_mid;
	}
	kvfree(page_array);
	*pages = new_array;
	*nr_pages = nr_folios;
	return true;
}

bool io_check_coalesce_buffer(struct page **page_array, int nr_pages,
			      struct io_imu_folio_data *data)
{
	struct folio *folio = page_folio(page_array[0]);
	unsigned int count = 1, nr_folios = 1;
	int i;

	data->nr_pages_mid = folio_nr_pages(folio);
	data->folio_shift = folio_shift(folio);

	/*
	 * Check if pages are contiguous inside a folio, and all folios have
	 * the same page count except for the head and tail.
	 */
	for (i = 1; i < nr_pages; i++) {
		if (page_folio(page_array[i]) == folio &&
			page_array[i] == page_array[i-1] + 1) {
			count++;
			continue;
		}

		if (nr_folios == 1) {
			if (folio_page_idx(folio, page_array[i-1]) !=
				data->nr_pages_mid - 1)
				return false;

			data->nr_pages_head = count;
		} else if (count != data->nr_pages_mid) {
			return false;
		}

		folio = page_folio(page_array[i]);
		if (folio_size(folio) != (1UL << data->folio_shift) ||
			folio_page_idx(folio, page_array[i]) != 0)
			return false;

		count = 1;
		nr_folios++;
	}
	if (nr_folios == 1)
		data->nr_pages_head = count;

	data->nr_folios = nr_folios;
	return true;
}

static struct io_rsrc_node *io_sqe_buffer_register(struct io_ring_ctx *ctx,
						   struct iovec *iov,
						   struct page **last_hpage)
{
	struct io_mapped_ubuf *imu = NULL;
	struct page **pages = NULL;
	struct io_rsrc_node *node;
	unsigned long off;
	size_t size;
	int ret, nr_pages, i;
	struct io_imu_folio_data data;
	bool coalesced = false;

	if (!iov->iov_base)
		return NULL;

	node = io_rsrc_node_alloc(IORING_RSRC_BUFFER);
	if (!node)
		return ERR_PTR(-ENOMEM);
	node->buf = NULL;

	ret = -ENOMEM;
	pages = io_pin_pages((unsigned long) iov->iov_base, iov->iov_len,
				&nr_pages);
	if (IS_ERR(pages)) {
		ret = PTR_ERR(pages);
		pages = NULL;
		goto done;
	}

	/* If it's huge page(s), try to coalesce them into fewer bvec entries */
	if (nr_pages > 1 && io_check_coalesce_buffer(pages, nr_pages, &data)) {
		if (data.nr_pages_mid != 1)
			coalesced = io_coalesce_buffer(&pages, &nr_pages, &data);
	}

	imu = kvmalloc(struct_size(imu, bvec, nr_pages), GFP_KERNEL);
	if (!imu)
		goto done;

	ret = io_buffer_account_pin(ctx, pages, nr_pages, imu, last_hpage);
	if (ret) {
		unpin_user_pages(pages, nr_pages);
		goto done;
	}

	size = iov->iov_len;
	/* store original address for later verification */
	imu->ubuf = (unsigned long) iov->iov_base;
	imu->len = iov->iov_len;
	imu->nr_bvecs = nr_pages;
	imu->folio_shift = PAGE_SHIFT;
	if (coalesced)
		imu->folio_shift = data.folio_shift;
	refcount_set(&imu->refs, 1);
	off = (unsigned long) iov->iov_base & ((1UL << imu->folio_shift) - 1);
	node->buf = imu;
	ret = 0;

	for (i = 0; i < nr_pages; i++) {
		size_t vec_len;

		vec_len = min_t(size_t, size, (1UL << imu->folio_shift) - off);
		bvec_set_page(&imu->bvec[i], pages[i], vec_len, off);
		off = 0;
		size -= vec_len;
	}
done:
	if (ret) {
		kvfree(imu);
		if (node)
			io_put_rsrc_node(ctx, node);
		node = ERR_PTR(ret);
	}
	kvfree(pages);
	return node;
}

int io_sqe_buffers_register(struct io_ring_ctx *ctx, void __user *arg,
			    unsigned int nr_args, u64 __user *tags)
{
	struct page *last_hpage = NULL;
	struct io_rsrc_data data;
	struct iovec fast_iov, *iov = &fast_iov;
	const struct iovec __user *uvec;
	int i, ret;

	BUILD_BUG_ON(IORING_MAX_REG_BUFFERS >= (1u << 16));

	if (ctx->buf_table.nr)
		return -EBUSY;
	if (!nr_args || nr_args > IORING_MAX_REG_BUFFERS)
		return -EINVAL;
	ret = io_rsrc_data_alloc(&data, nr_args);
	if (ret)
		return ret;

	if (!arg)
		memset(iov, 0, sizeof(*iov));

	for (i = 0; i < nr_args; i++) {
		struct io_rsrc_node *node;
		u64 tag = 0;

		if (arg) {
			uvec = (struct iovec __user *) arg;
			iov = iovec_from_user(uvec, 1, 1, &fast_iov, ctx->compat);
			if (IS_ERR(iov)) {
				ret = PTR_ERR(iov);
				break;
			}
			ret = io_buffer_validate(iov);
			if (ret)
				break;
			if (ctx->compat)
				arg += sizeof(struct compat_iovec);
			else
				arg += sizeof(struct iovec);
		}

		if (tags) {
			if (copy_from_user(&tag, &tags[i], sizeof(tag))) {
				ret = -EFAULT;
				break;
			}
		}

		node = io_sqe_buffer_register(ctx, iov, &last_hpage);
		if (IS_ERR(node)) {
			ret = PTR_ERR(node);
			break;
		}
		if (tag) {
			if (!node) {
				ret = -EINVAL;
				break;
			}
			node->tag = tag;
		}
		data.nodes[i] = node;
	}

	ctx->buf_table = data;
	if (ret) {
		io_clear_table_tags(&ctx->buf_table);
		io_sqe_buffers_unregister(ctx);
	}
	return ret;
}

int io_import_fixed(int ddir, struct iov_iter *iter,
			   struct io_mapped_ubuf *imu,
			   u64 buf_addr, size_t len)
{
	u64 buf_end;
	size_t offset;

	if (WARN_ON_ONCE(!imu))
		return -EFAULT;
	if (unlikely(check_add_overflow(buf_addr, (u64)len, &buf_end)))
		return -EFAULT;
	/* not inside the mapped region */
	if (unlikely(buf_addr < imu->ubuf || buf_end > (imu->ubuf + imu->len)))
		return -EFAULT;

	/*
	 * Might not be a start of buffer, set size appropriately
	 * and advance us to the beginning.
	 */
	offset = buf_addr - imu->ubuf;
	iov_iter_bvec(iter, ddir, imu->bvec, imu->nr_bvecs, len);

	if (offset) {
		/*
		 * Don't use iov_iter_advance() here, as it's really slow for
		 * using the latter parts of a big fixed buffer - it iterates
		 * over each segment manually. We can cheat a bit here, because
		 * we know that:
		 *
		 * 1) it's a BVEC iter, we set it up
		 * 2) all bvecs are the same in size, except potentially the
		 *    first and last bvec
		 *
		 * So just find our index, and adjust the iterator afterwards.
		 * If the offset is within the first bvec (or the whole first
		 * bvec, just use iov_iter_advance(). This makes it easier
		 * since we can just skip the first segment, which may not
		 * be folio_size aligned.
		 */
		const struct bio_vec *bvec = imu->bvec;

		if (offset < bvec->bv_len) {
			iter->iov_offset = offset;
		} else {
			unsigned long seg_skip;

			/* skip first vec */
			offset -= bvec->bv_len;
			seg_skip = 1 + (offset >> imu->folio_shift);

			iter->bvec += seg_skip;
			iter->nr_segs -= seg_skip;
			iter->iov_offset = offset & ((1UL << imu->folio_shift) - 1);
		}
	}

	return 0;
}

/* Lock two rings at once. The rings must be different! */
static void lock_two_rings(struct io_ring_ctx *ctx1, struct io_ring_ctx *ctx2)
{
	if (ctx1 > ctx2)
		swap(ctx1, ctx2);
	mutex_lock(&ctx1->uring_lock);
	mutex_lock_nested(&ctx2->uring_lock, SINGLE_DEPTH_NESTING);
}

/* Both rings are locked by the caller. */
static int io_clone_buffers(struct io_ring_ctx *ctx, struct io_ring_ctx *src_ctx,
			    struct io_uring_clone_buffers *arg)
{
	struct io_rsrc_data data;
	int i, ret, off, nr;
	unsigned int nbufs;

	lockdep_assert_held(&ctx->uring_lock);
	lockdep_assert_held(&src_ctx->uring_lock);

	/*
	 * Accounting state is shared between the two rings; that only works if
	 * both rings are accounted towards the same counters.
	 */
	if (ctx->user != src_ctx->user || ctx->mm_account != src_ctx->mm_account)
		return -EINVAL;

	/* if offsets are given, must have nr specified too */
	if (!arg->nr && (arg->dst_off || arg->src_off))
		return -EINVAL;
	/* not allowed unless REPLACE is set */
	if (ctx->buf_table.nr && !(arg->flags & IORING_REGISTER_DST_REPLACE))
		return -EBUSY;

	nbufs = src_ctx->buf_table.nr;
	if (!arg->nr)
		arg->nr = nbufs;
	else if (arg->nr > nbufs)
		return -EINVAL;
	else if (arg->nr > IORING_MAX_REG_BUFFERS)
		return -EINVAL;
	if (check_add_overflow(arg->nr, arg->dst_off, &nbufs))
		return -EOVERFLOW;

	ret = io_rsrc_data_alloc(&data, max(nbufs, ctx->buf_table.nr));
	if (ret)
		return ret;

	/* Fill entries in data from dst that won't overlap with src */
	for (i = 0; i < min(arg->dst_off, ctx->buf_table.nr); i++) {
		struct io_rsrc_node *src_node = ctx->buf_table.nodes[i];

		if (src_node) {
			data.nodes[i] = src_node;
			src_node->refs++;
		}
	}

	ret = -ENXIO;
	nbufs = src_ctx->buf_table.nr;
	if (!nbufs)
		goto out_free;
	ret = -EINVAL;
	if (!arg->nr)
		arg->nr = nbufs;
	else if (arg->nr > nbufs)
		goto out_free;
	ret = -EOVERFLOW;
	if (check_add_overflow(arg->nr, arg->src_off, &off))
		goto out_free;
	if (off > nbufs)
		goto out_free;

	off = arg->dst_off;
	i = arg->src_off;
	nr = arg->nr;
	while (nr--) {
		struct io_rsrc_node *dst_node, *src_node;

		src_node = io_rsrc_node_lookup(&src_ctx->buf_table, i);
		if (!src_node) {
			dst_node = NULL;
		} else {
			dst_node = io_rsrc_node_alloc(IORING_RSRC_BUFFER);
			if (!dst_node) {
				ret = -ENOMEM;
				goto out_free;
			}

			refcount_inc(&src_node->buf->refs);
			dst_node->buf = src_node->buf;
		}
		data.nodes[off++] = dst_node;
		i++;
	}

	/*
	 * If asked for replace, put the old table. data->nodes[] holds both
	 * old and new nodes at this point.
	 */
	if (arg->flags & IORING_REGISTER_DST_REPLACE)
		io_rsrc_data_free(ctx, &ctx->buf_table);

	/*
	 * ctx->buf_table must be empty now - either the contents are being
	 * replaced and we just freed the table, or the contents are being
	 * copied to a ring that does not have buffers yet (checked at function
	 * entry).
	 */
	WARN_ON_ONCE(ctx->buf_table.nr);
	ctx->buf_table = data;
	return 0;

out_free:
	io_rsrc_data_free(ctx, &data);
	return ret;
}

/*
 * Copy the registered buffers from the source ring whose file descriptor
 * is given in the src_fd to the current ring. This is identical to registering
 * the buffers with ctx, except faster as mappings already exist.
 *
 * Since the memory is already accounted once, don't account it again.
 */
int io_register_clone_buffers(struct io_ring_ctx *ctx, void __user *arg)
{
	struct io_uring_clone_buffers buf;
	struct io_ring_ctx *src_ctx;
	bool registered_src;
	struct file *file;
	int ret;

	if (copy_from_user(&buf, arg, sizeof(buf)))
		return -EFAULT;
	if (buf.flags & ~(IORING_REGISTER_SRC_REGISTERED|IORING_REGISTER_DST_REPLACE))
		return -EINVAL;
	if (!(buf.flags & IORING_REGISTER_DST_REPLACE) && ctx->buf_table.nr)
		return -EBUSY;
	if (memchr_inv(buf.pad, 0, sizeof(buf.pad)))
		return -EINVAL;

	registered_src = (buf.flags & IORING_REGISTER_SRC_REGISTERED) != 0;
	file = io_uring_register_get_file(buf.src_fd, registered_src);
	if (IS_ERR(file))
		return PTR_ERR(file);

	src_ctx = file->private_data;
	if (src_ctx != ctx) {
		mutex_unlock(&ctx->uring_lock);
		lock_two_rings(ctx, src_ctx);
	}

	ret = io_clone_buffers(ctx, src_ctx, &buf);

	if (src_ctx != ctx)
		mutex_unlock(&src_ctx->uring_lock);

	fput(file);
	return ret;
}