From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 95B301A3035; Sun, 24 Nov 2024 12:41:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452112; cv=none; b=Wle0QHKH68/inJqFx54CBuT4tdWi6FDoholtGiyaJxGUhy+QFT9k73Z3PYeAl5WmY7+kPfqnkHTiHWkMs+mAlIOkPohgUlweYIZPeaS0S6VjlsTZimbjxjbzrBOgdtnoluCcBPiSTYGMe/Hj3i5giqEvYVMW+C6RSRTZ3hSYPh0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452112; c=relaxed/simple; bh=ICKaszo58/M5MTx56qX3+bvtjH6Qm1RGqc6/gEmFHjY=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=RDZvIJ+E1pnw/QRmYd9jjwnxEdu3EWhvg1LkUzqHJuYA7QHsSv6hNmD+am7zdIUF0y1z6YpDlaMhuPGawk9WgCVszPKKXumjJlaRD9C3XZaUlzVFd/KNlw/bRbG2ZiaBw6APtAuFaqOa3Y1Ci331I717uudUhWKApyjctbD5+Ds= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UVdgOD/6; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="UVdgOD/6" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3DD3FC4CECC; Sun, 24 Nov 2024 12:41:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732452112; bh=ICKaszo58/M5MTx56qX3+bvtjH6Qm1RGqc6/gEmFHjY=; h=From:To:Cc:Subject:Date:From; b=UVdgOD/6SUSEPxCYvSubrs3tQoGa844K3nQHV9MWtP4j3ELy7hQDRoHPexy8pNyRw 7uerOq2q8hNQUmBrHj32gRUdNGUDi/k+BAlWcyD2FFb4MHmYCE6l8Iykg1De5HRL5/ ZkQ0DdYTINFOYIZKMX9izVplk/+dHJxKmLsoiap0guBJ/1tjYgnptFHuolbZR2px99 Lk6fdSo+u1j8mf7maE4KqRFTbltYvh23D3t7AqPVcHNANU9w+1oOneECRyfAPlXuWn ErXGWJMCbZDtjTkCktSLzn/BGRaLG7P9Ri++cD7bRlfbAmHjjEy+DGSXIvaHgA9TgU 002kVxfDvfWOg== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Christian Brauner , Jan Kara , syzbot+3b6b32dc50537a49bb4a@syzkaller.appspotmail.com, Sasha Levin , viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org Subject: [PATCH AUTOSEL 5.15 1/6] epoll: annotate racy check Date: Sun, 24 Nov 2024 07:41:37 -0500 Message-ID: <20241124124149.3336868-1-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.15.173 Content-Transfer-Encoding: 8bit From: Christian Brauner [ Upstream commit 6474353a5e3d0b2cf610153cea0c61f576a36d0a ] Epoll relies on a racy fastpath check during __fput() in eventpoll_release() to avoid the hit of pointlessly acquiring a semaphore. Annotate that race by using WRITE_ONCE() and READ_ONCE(). Link: https://lore.kernel.org/r/66edfb3c.050a0220.3195df.001a.GAE@google.com Link: https://lore.kernel.org/r/20240925-fungieren-anbauen-79b334b00542@brauner Reviewed-by: Jan Kara Reported-by: syzbot+3b6b32dc50537a49bb4a@syzkaller.appspotmail.com Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin --- fs/eventpoll.c | 6 ++++-- include/linux/eventpoll.h | 2 +- 2 files changed, 5 insertions(+), 3 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index b60edddf17870..7413b4a6ba282 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -696,7 +696,8 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi) to_free = NULL; head = file->f_ep; if (head->first == &epi->fllink && !epi->fllink.next) { - file->f_ep = NULL; + /* See eventpoll_release() for details. */ + WRITE_ONCE(file->f_ep, NULL); if (!is_file_epoll(file)) { struct epitems_head *v; v = container_of(head, struct epitems_head, epitems); @@ -1460,7 +1461,8 @@ static int attach_epitem(struct file *file, struct epitem *epi) spin_unlock(&file->f_lock); goto allocate; } - file->f_ep = head; + /* See eventpoll_release() for details. */ + WRITE_ONCE(file->f_ep, head); to_free = NULL; } hlist_add_head_rcu(&epi->fllink, file->f_ep); diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h index 3337745d81bd6..0c0d00fcd131f 100644 --- a/include/linux/eventpoll.h +++ b/include/linux/eventpoll.h @@ -42,7 +42,7 @@ static inline void eventpoll_release(struct file *file) * because the file in on the way to be removed and nobody ( but * eventpoll ) has still a reference to this file. */ - if (likely(!file->f_ep)) + if (likely(!READ_ONCE(file->f_ep))) return; /* -- 2.43.0