linux-kernel - Re: [PATCH 2/4] fuse: writepages: crop secondary requests

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Date:	Thu, 3 Oct 2013 17:14:32 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	Maxim Patlasov <mpatlasov@...allels.com>
Cc:	fuse-devel@...ts.sourceforge.net, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] fuse: writepages: crop secondary requests

On Thu, Oct 03, 2013 at 05:28:30PM +0400, Maxim Patlasov wrote:

> 1. There is an in-flight primary request with a chain of secondary ones.
> 2. User calls ftruncate(2) to extend file; fuse_set_nowrite() makes
> fi->writectr negative and starts waiting for completion of that
> in-flight request
> 3. Userspace fuse daemon ACKs the request and fuse_writepage_end()
> is called; it calls __fuse_flush_writepages(), but the latter does
> nothing because fi->writectr < 0
> 4. fuse_do_setattr() proceeds extending i_size and calling
> __fuse_release_nowrite(). But now new (increased) i_size will be
> used as 'crop' arg of __fuse_flush_writepages()
> 
> stale data can leak to the server.

So, lets do this then: skip fuse_flush_writepages() and call
fuse_send_writepage() directly.  It will ignore the NOWRITE logic, but that's
okay, this happens rarely and cannot happen more than once in a row.

Does this look good?

Can you actually trigger this path with your testing?

Thanks,
Miklos


Index: linux/fs/fuse/file.c
===================================================================
--- linux.orig/fs/fuse/file.c	2013-10-03 12:12:33.480918954 +0200
+++ linux/fs/fuse/file.c	2013-10-03 17:06:23.702510854 +0200
@@ -1436,12 +1436,12 @@ static void fuse_writepage_finish(struct
 }
 
 /* Called under fc->lock, may release and reacquire it */
-static void fuse_send_writepage(struct fuse_conn *fc, struct fuse_req *req)
+static void fuse_send_writepage(struct fuse_conn *fc, struct fuse_req *req,
+				loff_t size)
 __releases(fc->lock)
 __acquires(fc->lock)
 {
 	struct fuse_inode *fi = get_fuse_inode(req->inode);
-	loff_t size = i_size_read(req->inode);
 	struct fuse_write_in *inarg = &req->misc.write.in;
 	__u64 data_size = req->num_pages * PAGE_CACHE_SIZE;
 
@@ -1482,12 +1482,13 @@ __acquires(fc->lock)
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	struct fuse_inode *fi = get_fuse_inode(inode);
+	size_t crop = i_size_read(inode);
 	struct fuse_req *req;
 
 	while (fi->writectr >= 0 && !list_empty(&fi->queued_writes)) {
 		req = list_entry(fi->queued_writes.next, struct fuse_req, list);
 		list_del_init(&req->list);
-		fuse_send_writepage(fc, req);
+		fuse_send_writepage(fc, req, crop);
 	}
 }
 
@@ -1499,12 +1500,13 @@ static void fuse_writepage_end(struct fu
 	mapping_set_error(inode->i_mapping, req->out.h.error);
 	spin_lock(&fc->lock);
 	while (req->misc.write.next) {
+		struct fuse_conn *fc = get_fuse_conn(inode);
+		struct fuse_write_in *inarg = &req->misc.write.in;
 		struct fuse_req *next = req->misc.write.next;
 		req->misc.write.next = next->misc.write.next;
 		next->misc.write.next = NULL;
 		list_add(&next->writepages_entry, &fi->writepages);
-		list_add_tail(&next->list, &fi->queued_writes);
-		fuse_flush_writepages(inode);
+		fuse_send_writepage(fc, next, inarg->offset + inarg->size);
 	}
 	fi->writectr--;
 	fuse_writepage_finish(fc, req);
--
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