linux-kernel - [RFC PATCH 10/10] pipe: Check for ring full inside of the spinlock in pipe

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Message-ID: <157186191654.3995.6474781916564747415.stgit@warthog.procyon.org.uk>
Date:   Wed, 23 Oct 2019 21:18:36 +0100
From:   David Howells <dhowells@...hat.com>
To:     torvalds@...ux-foundation.org
Cc:     dhowells@...hat.com, Rasmus Villemoes <linux@...musvillemoes.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        nicolas.dichtel@...nd.com, raven@...maw.net,
        Christian Brauner <christian@...uner.io>, dhowells@...hat.com,
        keyrings@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-block@...r.kernel.org, linux-security-module@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 10/10] pipe: Check for ring full inside of the spinlock
 in pipe_write() [ver #2]

Make pipe_write() check to see if the ring has become full between it
taking the pipe mutex, checking the ring status and then taking the
spinlock.

This can happen if a notification is written into the pipe as that happens
without the pipe mutex.

Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/pipe.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/pipe.c b/fs/pipe.c
index 3df93990dd9d..6a982a88f658 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -462,6 +462,11 @@ pipe_write(struct kiocb *iocb, struct iov_iter *from)
 			spin_lock_irq(&pipe->wait.lock);
 
 			head = pipe->head;
+			if (pipe_full(head, pipe->tail, max_usage)) {
+				spin_unlock_irq(&pipe->wait.lock);
+				continue;
+			}
+
 			pipe_commit_write(pipe, head + 1);
 
 			/* Always wake up, even if the copy fails. Otherwise