linux-kernel - [PATCH] fuse: Fix fuse_get_user

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Message-Id: <1461105785-83223-1-git-send-email-seth.forshee@canonical.com>
Date:	Tue, 19 Apr 2016 17:43:04 -0500
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Seth Forshee <seth.forshee@...onical.com>,
	fuse-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: [PATCH] fuse: Fix fuse_get_user_pages() return value

fuse_direct_io() expects this to return either 0 or a negative
error code, but on success it may return a positive value.
fuse_direct_io() may return this same value when the subsequent
I/O operation doesn't transfer any data, which means that it will
return a positive value when no bytes were transferred. This is
obviously problematic.

Fix fuse_get_user_pages() to return 0 on success. This will in
turn make it so that fuse_direct_io() returns 0 if no bytes are
transferred.

Fixes: 742f992708df ("fuse: return patrial success from fuse_direct_io()")
Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
---
 fs/fuse/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index b5c616c5ec98..78af5c0996b8 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1295,7 +1295,7 @@ static int fuse_get_user_pages(struct fuse_req *req, struct iov_iter *ii,

 	*nbytesp = nbytes;

-	return ret;
+	return ret < 0 ? ret : 0;
 }

 static inline int fuse_iter_npages(const struct iov_iter *ii_p)
-- 
1.9.1