linux-kernel - [RFC PATCH 10/11] pipe: Check for ring full inside of the spinlock in pipe

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Message-ID: <157262973277.13142.11996381016183033698.stgit@warthog.procyon.org.uk>
Date:   Fri, 01 Nov 2019 17:35:32 +0000
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 10/11] pipe: Check for ring full inside of the spinlock
 in pipe_write() [ver #3]

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 d7b8d3f22987..aba2455caabe 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -463,6 +463,11 @@ 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->head = head + 1;
 
 			/* Always wake up, even if the copy fails. Otherwise