linux-kernel - [PATCH] fs/pipe: allow sendfile() to pipe again

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Message-Id: <20210125101615.efceefcaeae0.Ibe2d56dfaa49d7a366c835b5ae0f0a5c2d643ede@changeid>
Date:   Mon, 25 Jan 2021 10:16:15 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@....de>,
        Oliver Giles <ohw.giles@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH] fs/pipe: allow sendfile() to pipe again

After commit 36e2c7421f02 ("fs: don't allow splice read/write
without explicit ops") sendfile() could no longer send data
from a real file to a pipe, breaking for example certain cgit
setups (e.g. when running behind fcgiwrap), because in this
case cgit will try to do exactly this: sendfile() to a pipe.

Fix this by using iter_file_splice_write for the splice_write
method of pipes, as suggested by Christoph.

Cc: stable@...r.kernel.org
Fixes: 36e2c7421f02 ("fs: don't allow splice read/write without explicit ops")
Suggested-by: Christoph Hellwig <hch@....de>
Tested-by: Johannes Berg <johannes@...solutions.net>
Signed-off-by: Johannes Berg <johannes@...solutions.net>
---
Mostly for the record, since it looks like we'll have a proper
fix without another intermediate pipe. However, this fixes the
regression for now.
---
 fs/pipe.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/pipe.c b/fs/pipe.c
index c5989cfd564d..39c96845a72f 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1206,6 +1206,7 @@ const struct file_operations pipefifo_fops = {
 	.unlocked_ioctl	= pipe_ioctl,
 	.release	= pipe_release,
 	.fasync		= pipe_fasync,
+	.splice_write	= iter_file_splice_write,
 };
 
 /*
-- 
2.26.2