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[157.230.128.187]) by smtp.gmail.com with ESMTPSA id h193sm1001007pfe.30.2020.04.29.04.45.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Apr 2020 04:45:43 -0700 (PDT) Received: by 42.do-not-panic.com (Postfix, from userid 1000) id A8F8E403AB; Wed, 29 Apr 2020 11:45:42 +0000 (UTC) Date: Wed, 29 Apr 2020 11:45:42 +0000 From: Luis Chamberlain To: Christoph Hellwig Cc: axboe@kernel.dk, viro@zeniv.linux.org.uk, bvanassche@acm.org, gregkh@linuxfoundation.org, rostedt@goodmis.org, mingo@redhat.com, jack@suse.cz, ming.lei@redhat.com, nstange@suse.de, akpm@linux-foundation.org, mhocko@suse.com, yukuai3@huawei.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 v3 4/6] blktrace: fix debugfs use after free Message-ID: <20200429114542.GJ11244@42.do-not-panic.com> References: <20200429074627.5955-1-mcgrof@kernel.org> <20200429074627.5955-5-mcgrof@kernel.org> <20200429112637.GD21892@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200429112637.GD21892@infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) 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, Apr 29, 2020 at 04:26:37AM -0700, Christoph Hellwig wrote: > I can't say I'm a fan of all these long backtraces in commit logs.. > > > +static struct dentry *blk_debugfs_dir_register(const char *name) > > +{ > > + return debugfs_create_dir(name, blk_debugfs_root); > > +} > > I don't think we really need this helper. We don't export blk_debugfs_root, didn't think we'd want to, and since only a few scew funky drivers would use the struct gendisk and also support BLKTRACE, I didn't think we'd want to export it now. A new block private symbol namespace alright? > > +void blk_part_debugfs_unregister(struct hd_struct *p) > > +{ > > + debugfs_remove_recursive(p->debugfs_dir); > > + p->debugfs_dir = NULL; > > +} > > Why do we need to clear the pointer here? True, not needed for partition. > > +#ifdef CONFIG_DEBUG_FS > > + /* Currently only used by kernel/trace/blktrace.c */ > > + struct dentry *debugfs_dir; > > +#endif > > Does that comment really add value? I'll nuke it. > > +static struct dentry *blk_trace_debugfs_dir(struct block_device *bdev, > > + struct request_queue *q) > > { > > + struct hd_struct *p = NULL; > > > > + * Some drivers like scsi-generic use a NULL block device. For > > + * other drivers when bdev != bdev->bd_contain we are doing a blktrace > > + * on a parition, otherwise we know we are working on the whole > > + * disk, and for that the request_queue already has its own debugfs_dir. > > + * which we have been using for other things other than blktrace. > > + */ > > + if (bdev && bdev != bdev->bd_contains) > > + p = bdev->bd_part; > > > > + if (p) > > + return p->debugfs_dir; > > + > > + return q->debugfs_dir; > > This could be simplified down to: > > if (bdev && bdev != bdev->bd_contains) > return bdev->bd_part->debugfs_dir; > return q->debugfs_dir; > > Given that bd_part is in __blkdev_get very near bd_contains. Ah neat. > Also given that this patch completely rewrites blk_trace_debugfs_dir is > there any point in the previous patch? Still think it helps with making this patch easier to read, but I don't care, lemme know if I should just fold it. > > @@ -491,6 +500,7 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev, > > struct dentry *dir = NULL; > > int ret; > > > > + > > if (!buts->buf_size || !buts->buf_nr) > > return -EINVAL; > > > > Spurious whitespace change. Will nuke. Luis