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 672CA5304BF; Wed, 30 Sep 2026 18:25:01 +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=1790792702; cv=none; b=BhsuvcAkbNPkS5/z2ObvCASXruIp8gYBWr8McRKCDCIkqrBu/EA268MfNlOSUeG/hVUhpjd7/AHAsvMGthv5848PuvZuXoS9CsjaayqqDkAlUrE8ftoiQ0wTBUQmHzAdF5+8Zkr7GHgxV+lBklQtAm5R1nyJuSNdBneC2dS411w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790792702; c=relaxed/simple; bh=L/Mee07QD+kS885w74dQKXeq1DqNDRb2vGE5rML45nY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=P+lSSMfcz9pLeZgVg+BJQ3f/FTcb+/e0zCeWXn/oc99OT5m7WOcdeak9ylIGGch+tQD1VYkU68P3+yToqdL2SZLUnRgnaB7V5EO4aesO6wfY9jmg9OtoJZZPZxxnHYJnCNPrw/MuxJE220eveeO/V3BfKtKbyoQe4FDhzbH7am8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ud8URErt; 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="ud8URErt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C28121F000FF; Wed, 30 Sep 2026 18:25:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1790792701; bh=7R/+3/H0zJl9H1KGxKT2KEi7HY6zHYtF4gGI9A2PNeo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=ud8URErttjlfXgsBrdzIDOdNWQJcm3TXYQrvc4Z1Pt0zJO/41g/7CWCVTxZoMv1+i Mu4iMn4Kc7lhfyz9QzRSLzyU8qpLI/o1Oej2xFitTg58lyKAP4iurroKfQ/4ltTRVD +Yblv5xCNErlzr1mWMrJEgonzpA6E16x/dhQw8rc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Christian Brauner (Amutable)" , Quentin Schulz , Wentao Guan , Lee Jones , Sasha Levin Subject: [PATCH 5.15 746/752] eventpoll: move epi_fget() up Date: Wed, 30 Sep 2026 17:30:16 +0200 Message-ID: <20260930152414.359131362@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260930152358.131179731@linuxfoundation.org> References: <20260930152358.131179731@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-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") [file_ref_get(&file->f_ref) from original commit left as atomic_long_inc_not_zero(&file->f_count) due to v6.12.y missing commit 90ee6ed776c0 ("fs: port files to file_ref") and its dependent commit 08ef26ea9ab3 ("fs: add file_ref")] Signed-off-by: Quentin Schulz Signed-off-by: Wentao Guan Signed-off-by: Greg Kroah-Hartman (cherry picked from commit 7859566c519c75965b57ab2caccf8d6268717c9a) Signed-off-by: Lee Jones 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 3c5151e08f63b..95d31d23db60b 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -708,6 +708,34 @@ 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 (!atomic_long_inc_not_zero(&file->f_count)) + file = NULL; + return file; +} + /* * Called with &file->f_lock held, * returns with it released @@ -879,34 +907,6 @@ 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 (!atomic_long_inc_not_zero(&file->f_count)) - 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