From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi1-f182.google.com (mail-oi1-f182.google.com [209.85.167.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BFF8A27874F for ; Tue, 19 May 2026 11:29:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779190145; cv=none; b=GCwYGyETpWPvFlQfNI/Vpd75AAmPhaUitwH+tLQQ9IW9p+/RAtaY2vXPa06y3wf4IXZQWcsQdyuptiZ6VzB7q9SDp3s91hAyzou+gmRtVeRENdJJKVOw6MzhOsBq9zkp+Ydir5B2W0XX6XoXUIJ5O+JL8G7Da3WkUGtBJWngR6c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779190145; c=relaxed/simple; bh=szo2VVDxR9awOEL/+X182mFYbjmEhAJ/MspfhKVa/3k=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=LKlSlNis8Watdze1yTETzZbo7w5esYbQNj5/B3NpvsUYaBziewu5vLt05Q1I/fBKCnxZJb5SXbjBJR2IkH8ib8dfelp1i9y4c+clh9S0fiAEZlnOZt2Fm1e0vjPFASm0I2mEWY/0Pxt2mJzmvI2+0v5obXfDW13HSsySRCcQblI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=KlUvSxdo; arc=none smtp.client-ip=209.85.167.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KlUvSxdo" Received: by mail-oi1-f182.google.com with SMTP id 5614622812f47-47c918c62b4so2255301b6e.0 for ; Tue, 19 May 2026 04:29:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1779190143; x=1779794943; darn=vger.kernel.org; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:from:to :cc:subject:date:message-id:reply-to; bh=QSDvgGmb6zPH7zSSup9Opz0c2vS1ZlQJf1syzf4z968=; b=KlUvSxdoijGpdTCeGAymxdZtJDreqRkSYTSwq5ZtF3Mj/d7OL2IznxQ5vfu1FcmBFh 3Byh2plqf1kjssjOk5XZ+Fwp2qmilerBFmzUegxOQ562QjI7Ur/umkyYwPsm0SU1zXWw V/O1jUo0vwewSS2yy02Xmiju0Qbd3Mh6/eBOgG6SZ8rv23ZJu72EE9q3Qve0THgdHU7j 61iutM3djs1COoXJqoYQoCQxEhq9Bi3iRHnEkoVLRNTcBw2h2P3eTKB7gbGZBKVf9Qfz sVaszWdpd1u4fuXvi84yMypolL1tMF3iRsv6+fzEZD3V9W4AABqoMDWDGEdxb18//cUa 1SJQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1779190143; x=1779794943; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=QSDvgGmb6zPH7zSSup9Opz0c2vS1ZlQJf1syzf4z968=; b=YiTGzOYsMbuIyUNLsJjF/TG9W57LZ1bRcBvhQyXlg4GsPkvY2p1avV9auDNlILpmtr G7kQVZ4hyqw5PUGqOiKWQhCj3Vt0uDUso3ljtWzKVjhW7g/u+jnu6SkZBxm9iNtOWFIh 6kho/9/juw7QXgKPVDELNiv40LMw7kTrOLVRuMmCVQJD5ZUvQkrzuE1jLoB/mE5MqPvx 3MuXY2Y1Waod4+gLxon2qeCwmRPKaeGNJ2IPFX3omoQk4EhFxi2T9wAwmLcb0ajbtpa5 3dQSKb8PJR++K4fMbd9wKIRAjVuuz0h2Vt40MZV0eITqRMNP6iGkBr2VgX5YgPbcfKj1 upEQ== X-Forwarded-Encrypted: i=1; AFNElJ/I+Oe83H0yGzUF5M9yEsvRJKy5nOc2kpJiymEjgNt+6DFn2mPezna9ZUxP0LEvgwRBGhRuyg0N7fjepoM=@vger.kernel.org X-Gm-Message-State: AOJu0YyszwSqoOXlElSHHuplOCztj0ZaybiYE3JeONoDcfPn32kXvpbg YIb7SAacJOuCh638JrsiJ00sCEUEyuJ6/RnZVQjvm2oebGgH8lCnwkyC X-Gm-Gg: Acq92OGqooqi0b4V97VrVocx6LMzngH9yyJlk5fFhEdkTuDj77lXPXfZCPSxw5xoVk3 GZMX84zCHYr31HmHTy/mJG7VUKrBdHZICpGOw/OcyiZzbWnbX9qpMysD0P96VY+W1KEEW2T/8+5 EgOzw0Kj0nSnTXWPoP8Y8C3h6iYZIFKGGbMEBbMshBdnBzZ4gkDAR60hEEDeZAyT8byXJXwBLn8 kJDi5BQaaOz5BJkzCI4+fxSjGUlKHe9jyeuHXHq/7nAC38useVPM83fBjjzUT37ojvGBcpCg8QC Py5FQmL36bjqgHCwTTXl6QRqACi+CjJr5qc1TvfqS8Wu5B+1zp83dQYjJDXtbNcKpWnTOAKfiID UM419/2WhkhcNApf6pfOvQxjRUaTcO3dyZlL4hm025Bi60//AKwdsSi0vpkG0LfiBtU5LW2iz2C D1mBo1mUtOzF3/jnDJ74nw9kt/Akuoiscjc2/jTAAbQffjSV12QBfR+aPfk+r8MXA8qKR2MkhZ8 myxxkpcEylsowCwPZ5O X-Received: by 2002:a05:6808:c291:b0:467:70eb:36ae with SMTP id 5614622812f47-482e57c78c0mr12490521b6e.29.1779190142634; Tue, 19 May 2026 04:29:02 -0700 (PDT) Received: from fedora ([172.245.82.59]) by smtp.gmail.com with ESMTPSA id 5614622812f47-482ee0999f3sm6376418b6e.0.2026.05.19.04.28.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 May 2026 04:29:02 -0700 (PDT) Date: Tue, 19 May 2026 19:28:53 +0800 From: Ming Lei To: Hongling Zeng Cc: Hongling Zeng , axboe@kernel.dk, ming.lei@canonical.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Tetsuo Handa Subject: Re: [PATCH] block/loop: Fix NULL pointer dereference in lo_rw_aio() Message-ID: References: <20260519040103.22776-1-zenghongling@kylinos.cn> <6A0BFDE2.5000808@126.com> <6A0C29F6.5080704@126.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6A0C29F6.5080704@126.com> On Tue, May 19, 2026 at 05:14:30PM +0800, Hongling Zeng wrote: > Hi Ming, > > Tetsuo’s syzkaller trace confirms the root cause: > > Timeline: > T6142: lo_rw_aio(loop3) starting read with raw_refcnt=0x0, refcnt=1 > T44: lo_rw_aio(loop3) starting read with raw_refcnt=0x0, refcnt=1 > T6148: __loop_clr_fd(loop3) clearing lo_backing_file with raw_refcnt=0x0, > refcnt=1 > T180: lo_rw_aio(loop3) starting write with NULL file (already cleared?) > T180: CRASH - null-ptr-deref IO could be from writeback or early close, so the following patch should help: diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 0000913f7efc..24654a03db71 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1118,6 +1118,8 @@ static void __loop_clr_fd(struct loop_device *lo) struct file *filp; gfp_t gfp = lo->old_gfp_mask; + drain_workqueue(lo->workqueue); + spin_lock_irq(&lo->lo_lock); filp = lo->lo_backing_file; lo->lo_backing_file = NULL; @@ -1857,9 +1859,6 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx, blk_mq_start_request(rq); - if (data_race(READ_ONCE(lo->lo_state)) != Lo_bound) - return BLK_STS_IOERR; - switch (req_op(rq)) { case REQ_OP_FLUSH: case REQ_OP_DISCARD: @@ -1901,6 +1900,11 @@ static void loop_handle_cmd(struct loop_cmd *cmd) int ret = 0; struct mem_cgroup *old_memcg = NULL; + if (data_race(READ_ONCE(lo->lo_state)) != Lo_bound) { + ret = -EIO; + goto failed; + } + if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY)) { ret = -EIO; goto failed; > > Key anomaly: |raw_refcnt=0|while |refcnt=1|. > This means |__loop_clr_fd()|runs while I/O is still active. > Regression introduced by: > 6050fa4c84cc ("loop: don't hold lo_mutex during __loop_clr_fd()") Why do you conclude it is caused by above commit? Thanks, Ming