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[157.230.128.187]) by smtp.gmail.com with ESMTPSA id m7sm1026289pfb.1.2020.06.10.16.31.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Jun 2020 16:31:16 -0700 (PDT) Received: by 42.do-not-panic.com (Postfix, from userid 1000) id 0FDAA403AB; Wed, 10 Jun 2020 23:31:16 +0000 (UTC) Date: Wed, 10 Jun 2020 23:31:16 +0000 From: Luis Chamberlain To: Christoph Hellwig Cc: Jan Kara , axboe@kernel.dk, viro@zeniv.linux.org.uk, bvanassche@acm.org, gregkh@linuxfoundation.org, rostedt@goodmis.org, mingo@redhat.com, ming.lei@redhat.com, nstange@suse.de, akpm@linux-foundation.org, mhocko@suse.com, yukuai3@huawei.com, martin.petersen@oracle.com, jejb@linux.ibm.com, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Omar Sandoval , Hannes Reinecke , Michal Hocko , syzbot+603294af2d01acfdd6da@syzkaller.appspotmail.com Subject: Re: [PATCH v6 6/6] blktrace: fix debugfs use after free Message-ID: <20200610233116.GI13911@42.do-not-panic.com> References: <20200608170127.20419-1-mcgrof@kernel.org> <20200608170127.20419-7-mcgrof@kernel.org> <20200609150602.GA7111@infradead.org> <20200609172922.GP11244@42.do-not-panic.com> <20200609173218.GA7968@infradead.org> <20200609175359.GR11244@42.do-not-panic.com> <20200610064234.GB24975@infradead.org> <20200610210917.GH11244@42.do-not-panic.com> <20200610215213.GH13911@42.do-not-panic.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200610215213.GH13911@42.do-not-panic.com> X-Rspamd-Queue-Id: 95EC9100EDBE0 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jun 10, 2020 at 09:52:13PM +0000, Luis Chamberlain wrote: > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c > index 7ff2ea5cd05e..5cea04c05e09 100644 > --- a/kernel/trace/blktrace.c > +++ b/kernel/trace/blktrace.c > @@ -524,10 +524,16 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev, > if (!bt->msg_data) > goto err; > > - ret = -ENOENT; > - > - dir = debugfs_lookup(buts->name, blk_debugfs_root); > - if (!dir) > + /* > + * When tracing whole make_request drivers (multiqueue) block devices, > + * reuse the existing debugfs directory created by the block layer on > + * init. For request-based block devices, all partitions block devices, > + * and scsi-generic block devices we create a temporary new debugfs > + * directory that will be removed once the trace ends. > + */ > + if (queue_is_mq(q)) And this should be instead: if (queue_is_mq(q) && bdev && bdev == bdev->bd_contains) > + dir = q->debugfs_dir; > + else > bt->dir = dir = debugfs_create_dir(buts->name, blk_debugfs_root); > > bt->dev = dev; > @@ -565,8 +571,6 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev, > > ret = 0; > err: > - if (dir && !bt->dir) > - dput(dir); > if (ret) > blk_trace_free(bt); > return ret;