fuse: fix race in fuse_writepages() (2d033eaa) · Commits · 戴 / test

The patch fixes a race between ftruncate(2), mmap-ed write and write(2): 1) An user makes a page dirty via mmap-ed write. 2) The user performs shrinking truncate(2) intended to purge the page. 3) Before fuse_do_setattr calls truncate_pagecache, the page goes to writeback. fuse_writepages_fill attaches a new page to FUSE_WRITE request, then releases the original page by end_page_writeback and unlock it. 4) fuse_do_setattr completes and successfully returns. Since now, i_mutex is free. 5) Ordinary write(2) extends i_size back to cover the page. Note that fuse_send_write_pages do wait for fuse writeback, but for another page->index. 6) fuse_writepages_fill attaches more pages to the request (if any), then fuse_writepages_send is eventually called. It is supposed to crop inarg->size of the request, but it doesn't because i_size has already been extended back. Moving end_page_writeback behind fuse_writepages_send guarantees that __fuse_release_nowrite (called from fuse_do_setattr) will crop inarg->size of the request before write(2) gets the chance to extend i_size. Signed-off-by:

Maxim Patlasov <mpatlasov@parallels.com> Signed-off-by:

Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/file.c

+16 −1

Original line number	Diff line number	Diff line
		@@ -1590,6 +1590,7 @@ struct fuse_fill_wb_data {
		struct fuse_req *req;
		struct fuse_file *ff;
		struct inode *inode;
		struct page **orig_pages;
		};

		static void fuse_writepages_send(struct fuse_fill_wb_data *data)
		@@ -1598,12 +1599,17 @@ static void fuse_writepages_send(struct fuse_fill_wb_data *data)
		struct inode *inode = data->inode;
		struct fuse_conn *fc = get_fuse_conn(inode);
		struct fuse_inode *fi = get_fuse_inode(inode);
		int num_pages = req->num_pages;
		int i;

		req->ff = fuse_file_get(data->ff);
		spin_lock(&fc->lock);
		list_add_tail(&req->list, &fi->queued_writes);
		fuse_flush_writepages(inode);
		spin_unlock(&fc->lock);

		for (i = 0; i < num_pages; i++)
		end_page_writeback(data->orig_pages[i]);
		}

		static int fuse_writepages_fill(struct page *page,
		@@ -1684,7 +1690,7 @@ static int fuse_writepages_fill(struct page *page,

		inc_bdi_stat(page->mapping->backing_dev_info, BDI_WRITEBACK);
		inc_zone_page_state(tmp_page, NR_WRITEBACK_TEMP);
		end_page_writeback(page);
		data->orig_pages[req->num_pages] = page;

		/*
		* Protected by fc->lock against concurrent access by
		@@ -1716,6 +1722,13 @@ static int fuse_writepages(struct address_space *mapping,
		data.req = NULL;
		data.ff = NULL;

		err = -ENOMEM;
		data.orig_pages = kzalloc(sizeof(struct page )
		FUSE_MAX_PAGES_PER_REQ,
		GFP_NOFS);
		if (!data.orig_pages)
		goto out;

		err = write_cache_pages(mapping, wbc, fuse_writepages_fill, &data);
		if (data.req) {
		/* Ignore errors if we can write at least one page */
		@@ -1725,6 +1738,8 @@ static int fuse_writepages(struct address_space *mapping,
		}
		if (data.ff)
		fuse_file_put(data.ff, false);

		kfree(data.orig_pages);
		out:
		return err;
		}

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