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[73.241.217.19]) by smtp.gmail.com with ESMTPSA id z11sm9592511pfk.141.2020.06.20.10.31.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 20 Jun 2020 10:31:53 -0700 (PDT) Subject: Re: [PATCH v7 6/8] blktrace: fix debugfs use after free To: Luis Chamberlain , axboe@kernel.dk, viro@zeniv.linux.org.uk, gregkh@linuxfoundation.org, rostedt@goodmis.org, mingo@redhat.com, jack@suse.cz, ming.lei@redhat.com, nstange@suse.de, akpm@linux-foundation.org Cc: 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 References: <20200619204730.26124-1-mcgrof@kernel.org> <20200619204730.26124-7-mcgrof@kernel.org> From: Bart Van Assche Autocrypt: addr=bvanassche@acm.org; prefer-encrypt=mutual; keydata= mQENBFSOu4oBCADcRWxVUvkkvRmmwTwIjIJvZOu6wNm+dz5AF4z0FHW2KNZL3oheO3P8UZWr LQOrCfRcK8e/sIs2Y2D3Lg/SL7qqbMehGEYcJptu6mKkywBfoYbtBkVoJ/jQsi2H0vBiiCOy fmxMHIPcYxaJdXxrOG2UO4B60Y/BzE6OrPDT44w4cZA9DH5xialliWU447Bts8TJNa3lZKS1 AvW1ZklbvJfAJJAwzDih35LxU2fcWbmhPa7EO2DCv/LM1B10GBB/oQB5kvlq4aA2PSIWkqz4 3SI5kCPSsygD6wKnbRsvNn2mIACva6VHdm62A7xel5dJRfpQjXj2snd1F/YNoNc66UUTABEB AAG0JEJhcnQgVmFuIEFzc2NoZSA8YnZhbmFzc2NoZUBhY20ub3JnPokBOQQTAQIAIwUCVI67 igIbAwcLCQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEHFcPTXFzhAJ8QkH/1AdXblKL65M Y1Zk1bYKnkAb4a98LxCPm/pJBilvci6boefwlBDZ2NZuuYWYgyrehMB5H+q+Kq4P0IBbTqTa jTPAANn62A6jwJ0FnCn6YaM9TZQjM1F7LoDX3v+oAkaoXuq0dQ4hnxQNu792bi6QyVdZUvKc macVFVgfK9n04mL7RzjO3f+X4midKt/s+G+IPr4DGlrq+WH27eDbpUR3aYRk8EgbgGKvQFdD CEBFJi+5ZKOArmJVBSk21RHDpqyz6Vit3rjep7c1SN8s7NhVi9cjkKmMDM7KYhXkWc10lKx2 RTkFI30rkDm4U+JpdAd2+tP3tjGf9AyGGinpzE2XY1K5AQ0EVI67igEIAKiSyd0nECrgz+H5 PcFDGYQpGDMTl8MOPCKw/F3diXPuj2eql4xSbAdbUCJzk2ETif5s3twT2ER8cUTEVOaCEUY3 eOiaFgQ+nGLx4BXqqGewikPJCe+UBjFnH1m2/IFn4T9jPZkV8xlkKmDUqMK5EV9n3eQLkn5g lco+FepTtmbkSCCjd91EfThVbNYpVQ5ZjdBCXN66CKyJDMJ85HVr5rmXG/nqriTh6cv1l1Js T7AFvvPjUPknS6d+BETMhTkbGzoyS+sywEsQAgA+BMCxBH4LvUmHYhpS+W6CiZ3ZMxjO8Hgc ++w1mLeRUvda3i4/U8wDT3SWuHcB3DWlcppECLkAEQEAAYkBHwQYAQIACQUCVI67igIbDAAK CRBxXD01xc4QCZ4dB/0QrnEasxjM0PGeXK5hcZMT9Eo998alUfn5XU0RQDYdwp6/kMEXMdmT oH0F0xB3SQ8WVSXA9rrc4EBvZruWQ+5/zjVrhhfUAx12CzL4oQ9Ro2k45daYaonKTANYG22y //x8dLe2Fv1By4SKGhmzwH87uXxbTJAUxiWIi1np0z3/RDnoVyfmfbbL1DY7zf2hYXLLzsJR mSsED/1nlJ9Oq5fALdNEPgDyPUerqHxcmIub+pF0AzJoYHK5punqpqfGmqPbjxrJLPJfHVKy goMj5DlBMoYqEgpbwdUYkH6QdizJJCur4icy8GUNbisFYABeoJ91pnD4IGei3MTdvINSZI5e Message-ID: <75c3a94d-dcd1-05e4-47c6-db65f074136a@acm.org> Date: Sat, 20 Jun 2020 10:31:51 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200619204730.26124-7-mcgrof@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: E899D1804E3A1 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 2020-06-19 13:47, Luis Chamberlain wrote: > This goes tested with: ^^^^ got? > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c > index 7ff2ea5cd05e..e6e2d25fdbd6 100644 > --- a/kernel/trace/blktrace.c > +++ b/kernel/trace/blktrace.c > @@ -524,10 +524,18 @@ 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) > +#ifdef CONFIG_BLK_DEBUG_FS > + /* > + * 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, ^^^^^^^^^^^^^^^^^^^^^ It seems like a word is missing from the comment? Or did you perhaps want to refer to "all partition 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) && bdev && bdev == bdev->bd_contains) > + dir = q->debugfs_dir; > + else > +#endif > bt->dir = dir = debugfs_create_dir(buts->name, blk_debugfs_root); Can it happen that two different threads each try to set up block tracing and hence that debugfs_create_dir() fails because a directory with name buts->name already exists? > bt->dev = dev; > @@ -565,8 +573,6 @@ 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; Shouldn't bt->dir be removed in this error path for make_request drivers? Thanks, Bart.