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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+6e1efbd8efaaa6860e91@syzkaller.appspotmail.com,
        Miklos Szeredi <mszeredi@redhat.com>
Subject: [PATCH 5.18 0105/1095] fuse: write inode in fuse_release()
Date:   Mon, 15 Aug 2022 19:51:44 +0200
Message-Id: <20220815180433.905210062@linuxfoundation.org>
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From: Miklos Szeredi <mszeredi@redhat.com>

commit 035ff33cf4db101250fb980a3941bf078f37a544 upstream.

A race between write(2) and close(2) allows pages to be dirtied after
fuse_flush -> write_inode_now().  If these pages are not flushed from
fuse_release(), then there might not be a writable open file later.  So any
remaining dirty pages must be written back before the file is released.

This is a partial revert of the blamed commit.

Reported-by: syzbot+6e1efbd8efaaa6860e91@syzkaller.appspotmail.com
Fixes: 36ea23374d1f ("fuse: write inode in fuse_vma_close() instead of fuse_release()")
Cc: <stable@vger.kernel.org> # v5.16
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/fuse/file.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -338,6 +338,15 @@ static int fuse_open(struct inode *inode
 
 static int fuse_release(struct inode *inode, struct file *file)
 {
+	struct fuse_conn *fc = get_fuse_conn(inode);
+
+	/*
+	 * Dirty pages might remain despite write_inode_now() call from
+	 * fuse_flush() due to writes racing with the close.
+	 */
+	if (fc->writeback_cache)
+		write_inode_now(inode, 1);
+
 	fuse_release_common(file, false);
 
 	/* return value is ignored by VFS */