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 7E27B298C1B; Mon, 12 May 2025 18:04:26 +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=1747073066; cv=none; b=AE2hJyGNdd+i3N1upwih4Y9EShEQjEChDTq2BnP3q0Ek2Zm5FHPaFgvGMRpTCK7xN0QGGlsE7LWcRhSwPiDGZpsj1yrjGEypR/VCx3XKXT6MDHAJSOf8Usd/II4NbhNBsVH8+4A/euvtPSSWhvGnkyzseHYUFb16jDdP2o//Iks= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747073066; c=relaxed/simple; bh=UHCXy9jR8dSGqVN48aTVRaYvNMr8ifTKeSKvOn17H8w=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=IWJ0kwNXnOf2DAA27UogijYyEZToXkxD+Y/xCLsa7jvi/7Bg7JukGlJfBX7Le7QK/+50HydBMOM1wCXC/i157JXwnG5TZ7p+JEOii2pBtdfVHchNeWgX38RJx6lt/11YsPnQlIizg44QBpy617c46j3pGkSX6X5Apk6A27PEJgc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GIy+h3cG; 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="GIy+h3cG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 24A3CC4CEF0; Mon, 12 May 2025 18:04:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1747073066; bh=UHCXy9jR8dSGqVN48aTVRaYvNMr8ifTKeSKvOn17H8w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GIy+h3cGV028lDKoKPOQt8neYjnSnCIfJZL23jzQ2stNM3JIKGOIaG3qSXiQfRZM4 NE8qeKGSAParA1fkMHvjPHOhwuyDESiRRCGoSdfdFMVq/vc+cqaI5PKmN6N83HZ6Mm K0wPGu8coC+QHd334uMmognyvfpr8vW+JC9nzocYlTq5qxFOabDsc5jj6CfLrJjCQF THcrcSZtpXr+0Sp8lA/2BP0OoylpEC0X0+6cQn1TaNCvWKpp0HbAG65wV5tKE+RtIk n8OhnCuYpe3oo4w4Xw9tKIKtPWFdRq7Pckp/5R5lIs+Smq9F9jGYk0NURyUK2mFlx0 kBYIBi3Q9vVEQ== From: Sasha Levin To: patches@lists.linux.dev, stable@vger.kernel.org Cc: Al Viro , Christian Brauner , Sasha Levin , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH AUTOSEL 6.14 15/15] __legitimize_mnt(): check for MNT_SYNC_UMOUNT should be under mount_lock Date: Mon, 12 May 2025 14:03:50 -0400 Message-Id: <20250512180352.437356-15-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250512180352.437356-1-sashal@kernel.org> References: <20250512180352.437356-1-sashal@kernel.org> 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 6.14.6 Content-Transfer-Encoding: 8bit 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 280a6ebc46d93..6730ffb03da5b 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -781,12 +781,8 @@ int __legitimize_mnt(struct vfsmount *bastard, unsigned seq) smp_mb(); // see mntput_no_expire() 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