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 B0544224247; Mon, 2 Jun 2025 14:41:12 +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=1748875272; cv=none; b=Rxi/knYwvY4HNAYTB63wae9j3v38I4mI6DHjuEyN/RMz0WWhFqCz9r5WEHladuCG8rx7NVuW2GDRaq7YiV7tbYdTNQI1tKw5d2VQz5qO2hBkbeCY/sqL8Z7KMo1ogxGpXAkYsXKy8RclOXeKZeflIPkF8RcECKbuVq3Q9QI9InE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748875272; c=relaxed/simple; bh=U85LASC22LjKEJ25q0YN6rAPF9ca85mjadhb+Y4lGDI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=AQwaQvdNtXyapogluqtKzk1xJCA9q2B73VgrZvLKYvM/cioHIJ6q/A3636h32gMXOrUr2MTNE38hL11+QOm/GN1V4k7nbOUaoVOBiBZ7+nYTCCLdoeL/C1P2+NsAnMr7x2lai0ahNgntpUbqJjJpq5DAh4sTf6H2KHv/Ccfxk2Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=fx02iHdg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="fx02iHdg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 409C3C4CEEB; Mon, 2 Jun 2025 14:41:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1748875272; bh=U85LASC22LjKEJ25q0YN6rAPF9ca85mjadhb+Y4lGDI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fx02iHdgbwWstpDBgE4xKihiPYGNf3VnzMnYJNLoBO+PiMFzU9P7/R6Q7tfOWmK8G Ast1DlaC+BwKkGsRcwWhLEJSH3uy8iU+dR/qXTJP/0czeAD3SNBwyMnGpaiiDXxSPA erfUC8Egku0WCrIbKo2rLunDgJ/XE5wuhUFaWH2Y= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Christian Brauner , Al Viro , Sasha Levin Subject: [PATCH 5.10 082/270] do_umount(): add missing barrier before refcount checks in sync case Date: Mon, 2 Jun 2025 15:46:07 +0200 Message-ID: <20250602134310.525069482@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250602134307.195171844@linuxfoundation.org> References: <20250602134307.195171844@linuxfoundation.org> User-Agent: quilt/0.68 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 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro [ Upstream commit 65781e19dcfcb4aed1167d87a3ffcc2a0c071d47 ] do_umount() analogue of the race fixed in 119e1ef80ecf "fix __legitimize_mnt()/mntput() race". Here we want to make sure that if __legitimize_mnt() doesn't notice our lock_mount_hash(), we will notice their refcount increment. Harder to hit than mntput_no_expire() one, fortunately, and consequences are milder (sync umount acting like umount -l on a rare race with RCU pathwalk hitting at just the wrong time instead of use-after-free galore mntput_no_expire() counterpart used to be hit). Still a bug... Fixes: 48a066e72d97 ("RCU'd vfsmounts") Reviewed-by: Christian Brauner Signed-off-by: Al Viro Signed-off-by: Sasha Levin --- fs/namespace.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/namespace.c b/fs/namespace.c index 2f97112657adc..e46267e7d29d1 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -569,7 +569,7 @@ int __legitimize_mnt(struct vfsmount *bastard, unsigned seq) return 0; mnt = real_mount(bastard); mnt_add_count(mnt, 1); - smp_mb(); // see mntput_no_expire() + smp_mb(); // see mntput_no_expire() and do_umount() if (likely(!read_seqretry(&mount_lock, seq))) return 0; if (bastard->mnt_flags & MNT_SYNC_UMOUNT) { @@ -1638,6 +1638,7 @@ static int do_umount(struct mount *mnt, int flags) umount_tree(mnt, UMOUNT_PROPAGATE); retval = 0; } else { + smp_mb(); // paired with __legitimize_mnt() shrink_submounts(mnt); retval = -EBUSY; if (!propagate_mount_busy(mnt, 2)) { -- 2.39.5