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Date: Fri, 16 Aug 2013 15:51:41 +0400
From: Maxim Patlasov <MPatlasov@...allels.com>
To: miklos@...redi.hu
Cc: fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
devel@...nvz.org, xemul@...allels.com
Subject: [PATCH] fuse: fix race in fuse_writepages()
The patch is for
git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git writepages.v2
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@...allels.com>
---
fs/fuse/file.c | 17 ++++++++++++++++-
1 files changed, 16 insertions(+), 1 deletions(-)
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 568e859..0ebcc79 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1583,6 +1583,7 @@ 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)
@@ -1591,12 +1592,17 @@ 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,
@@ -1677,7 +1683,7 @@ 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
@@ -1709,6 +1715,13 @@ 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 */
@@ -1718,6 +1731,8 @@ 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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