From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E78A0233933; Wed, 20 May 2026 17:48:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779299302; cv=none; b=NE0pCCVDkDYkLyGaZlBH1Zjc3mQNjIdBFLNfUv0gjm11+XSOLbaGr9fMP15SDBi71Xkpp4g8/H9KHFfBk5MWKCF75IfDRVV5OWi+ysnJQmTxwVBXlwuYFe50PeSfrQlQ/lTUjPSExXg14oqwepCC9Mb4RYE6DKm65u0yUFabux8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779299302; c=relaxed/simple; bh=P+WRjTvVQrpA8pAiJ+bLcBJTKYyCobIDIGPRbRn4SXw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=e+aD7K5lvVwy6jZFL9fx6P3ksXeeOhbr4YestCsooUr8B4c/Me5F8+USv32D0Q8b6/TUZ48qT0OCKKnW8+SlfIzpv6qAFYIJ8KSNEXic8DhByzIjCOJAwTPDjiTZUOXoNnzbozSjp3cfIvk4dtAJDnk8cM/e8o+pHtHhzuUjE90= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=od1ksCc3; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="od1ksCc3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 214551F000E9; Wed, 20 May 2026 17:48:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1779299300; bh=xcZu6X//FpWRmEi3Lm3VquuHVUPpeyUdcQtfLT/ZCrY=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=od1ksCc3JC0db74cwrfPn1z3NdlXQ6TfEifHwp1O4BzkEKfW0cgIYAPqfgjk4zDqT lKgupYthaOBYX1OTa5Crxz+SbxBkotMvdlybEk947mDoNMoOTkqpOnDj/Ibb+rJ4bX 7U+1z7us+1a6VnGjrF6whF3PDaLbkcaYuMo0cLPE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Christian Brauner (Amutable)" , Sasha Levin Subject: [PATCH 6.18 721/957] eventpoll: move epi_fget() up Date: Wed, 20 May 2026 18:20:04 +0200 Message-ID: <20260520162150.185481131@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520162134.554764788@linuxfoundation.org> References: <20260520162134.554764788@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Brauner [ Upstream commit 86e87059e6d1fd5115a31949726450ed03c1073b ] We'll need it when removing files so move it up. No functional change. Link: https://patch.msgid.link/20260423-work-epoll-uaf-v1-5-2470f9eec0f5@kernel.org Signed-off-by: Christian Brauner (Amutable) Stable-dep-of: a6dc643c6931 ("eventpoll: fix ep_remove struct eventpoll / struct file UAF") Signed-off-by: Sasha Levin --- fs/eventpoll.c | 56 +++++++++++++++++++++++++------------------------- 1 file changed, 28 insertions(+), 28 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 68607634a60df..df6994943e59f 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -826,6 +826,34 @@ static void ep_free(struct eventpoll *ep) kfree_rcu(ep, rcu); } +/* + * The ffd.file pointer may be in the process of being torn down due to + * being closed, but we may not have finished eventpoll_release() yet. + * + * Normally, even with the atomic_long_inc_not_zero, the file may have + * been free'd and then gotten re-allocated to something else (since + * files are not RCU-delayed, they are SLAB_TYPESAFE_BY_RCU). + * + * But for epoll, users hold the ep->mtx mutex, and as such any file in + * the process of being free'd will block in eventpoll_release_file() + * and thus the underlying file allocation will not be free'd, and the + * file re-use cannot happen. + * + * For the same reason we can avoid a rcu_read_lock() around the + * operation - 'ffd.file' cannot go away even if the refcount has + * reached zero (but we must still not call out to ->poll() functions + * etc). + */ +static struct file *epi_fget(const struct epitem *epi) +{ + struct file *file; + + file = epi->ffd.file; + if (!file_ref_get(&file->f_ref)) + file = NULL; + return file; +} + /* * Called with &file->f_lock held, * returns with it released @@ -1018,34 +1046,6 @@ static __poll_t __ep_eventpoll_poll(struct file *file, poll_table *wait, int dep return res; } -/* - * The ffd.file pointer may be in the process of being torn down due to - * being closed, but we may not have finished eventpoll_release() yet. - * - * Normally, even with the atomic_long_inc_not_zero, the file may have - * been free'd and then gotten re-allocated to something else (since - * files are not RCU-delayed, they are SLAB_TYPESAFE_BY_RCU). - * - * But for epoll, users hold the ep->mtx mutex, and as such any file in - * the process of being free'd will block in eventpoll_release_file() - * and thus the underlying file allocation will not be free'd, and the - * file re-use cannot happen. - * - * For the same reason we can avoid a rcu_read_lock() around the - * operation - 'ffd.file' cannot go away even if the refcount has - * reached zero (but we must still not call out to ->poll() functions - * etc). - */ -static struct file *epi_fget(const struct epitem *epi) -{ - struct file *file; - - file = epi->ffd.file; - if (!file_ref_get(&file->f_ref)) - file = NULL; - return file; -} - /* * Differs from ep_eventpoll_poll() in that internal callers already have * the ep->mtx so we need to start from depth=1, such that mutex_lock_nested() -- 2.53.0