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 103AE22A7E4; Mon, 2 Jun 2025 14:59:46 +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=1748876386; cv=none; b=R9D5CmVlp1X4zTANu+B0h08hebj1H0rik9LYuZEoirBg9PkPH2UBn4UmPSvMPSbLig62g6zsYadOKGmdEuitYtWM/2/K2fbhh9YBNfu6KYQ2c8as9UUwvvcfbn5bKn0CwsxJ1k4y0IFPf6+CRrzlvtnzByhFj7Evl0VfPaMHzJ0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1748876386; c=relaxed/simple; bh=H3iabgjzWGDBvdWTXK+o1wcPcmY4lUN6/AiHT/EToq0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=bUybpb4AXUpDprw1thAk29fZ6AocH39qlKcMUv9rs6Hlc2nu/HVmjk6wrOc8TsPyvJF91iKlZ+nE1/+zLwhT/UNuyeacpp3xbgy9F02hC6A83+nYnaTYgJgW/RISeJ1yDeSrEmGhxwrirq3kyMonhcPcMgUbkMXv0DKJmMgH1oQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=be4Celva; 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="be4Celva" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8C9D7C4CEEB; Mon, 2 Jun 2025 14:59:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1748876385; bh=H3iabgjzWGDBvdWTXK+o1wcPcmY4lUN6/AiHT/EToq0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=be4CelvaDUdDiP1HvW+xVhaDwJpcizb05N5wZ/bIcNnozxHNZGRqdMK/UsvYHyCJB +fGEuvWAj1zCeTJmn0wyz4CjDIr7uK6P5ii3JBefZXIeeT4LTsSXHjLMxF7kO1qayl ZORS/yvdsTMcogCiBrnJEzpNu6k+kf/GWcsTkOWk= 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 5.15 161/207] __legitimize_mnt(): check for MNT_SYNC_UMOUNT should be under mount_lock Date: Mon, 2 Jun 2025 15:48:53 +0200 Message-ID: <20250602134305.026554807@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250602134258.769974467@linuxfoundation.org> References: <20250602134258.769974467@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 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Al Viro [ Upstream commit 250cf3693060a5f803c5f1ddc082bb06b16112a9 ] ... or we risk stealing final mntput from sync umount - raising mnt_count after umount(2) has verified that victim is not busy, but before it has set MNT_SYNC_UMOUNT; in that case __legitimize_mnt() doesn't see that it's safe to quietly undo mnt_count increment and leaves dropping the reference to caller, where it'll be a full-blown mntput(). Check under mount_lock is needed; leaving the current one done before taking that makes no sense - it's nowhere near common enough to bother with. Reviewed-by: Christian Brauner Signed-off-by: Al Viro Signed-off-by: Sasha Levin --- fs/namespace.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index 27ec6d0a68ff5..a99a060e89316 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -589,12 +589,8 @@ int __legitimize_mnt(struct vfsmount *bastard, unsigned seq) 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) { - mnt_add_count(mnt, -1); - return 1; - } lock_mount_hash(); - if (unlikely(bastard->mnt_flags & MNT_DOOMED)) { + if (unlikely(bastard->mnt_flags & (MNT_SYNC_UMOUNT | MNT_DOOMED))) { mnt_add_count(mnt, -1); unlock_mount_hash(); return 1; -- 2.39.5