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Wed, 15 Apr 2020 20:01:46 -0500 (CDT) Subject: Re: [PATCH 2/5] blktrace: fix debugfs use after free To: Luis Chamberlain 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 References: <20200414041902.16769-1-mcgrof@kernel.org> <20200414041902.16769-3-mcgrof@kernel.org> <55401e02-f61c-25eb-271c-3ec7baf35e28@sandeen.net> <20200416005636.GA11244@42.do-not-panic.com> From: Eric Sandeen Autocrypt: addr=sandeen@sandeen.net; prefer-encrypt=mutual; keydata= mQINBE6x99QBEADMR+yNFBc1Y5avoUhzI/sdR9ANwznsNpiCtZlaO4pIWvqQJCjBzp96cpCs nQZV32nqJBYnDpBDITBqTa/EF+IrHx8gKq8TaSBLHUq2ju2gJJLfBoL7V3807PQcI18YzkF+ WL05ODFQ2cemDhx5uLghHEeOxuGj+1AI+kh/FCzMedHc6k87Yu2ZuaWF+Gh1W2ix6hikRJmQ vj5BEeAx7xKkyBhzdbNIbbjV/iGi9b26B/dNcyd5w2My2gxMtxaiP7q5b6GM2rsQklHP8FtW ZiYO7jsg/qIppR1C6Zr5jK1GQlMUIclYFeBbKggJ9mSwXJH7MIftilGQ8KDvNuV5AbkronGC sEEHj2khs7GfVv4pmUUHf1MRIvV0x3WJkpmhuZaYg8AdJlyGKgp+TQ7B+wCjNTdVqMI1vDk2 BS6Rg851ay7AypbCPx2w4d8jIkQEgNjACHVDU89PNKAjScK1aTnW+HNUqg9BliCvuX5g4z2j gJBs57loTWAGe2Ve3cMy3VoQ40Wt3yKK0Eno8jfgzgb48wyycINZgnseMRhxc2c8hd51tftK LKhPj4c7uqjnBjrgOVaVBupGUmvLiePlnW56zJZ51BR5igWnILeOJ1ZIcf7KsaHyE6B1mG+X dmYtjDhjf3NAcoBWJuj8euxMB6TcQN2MrSXy5wSKaw40evooGwARAQABtCVFcmljIFIuIFNh bmRlZW4gPHNhbmRlZW5Ac2FuZGVlbi5uZXQ+iQI7BBMBAgAlAhsDBgsJCAcDAgYVCAIJCgsE FgIDAQIeAQIXgAUCUzMzbAIZAQAKCRAgrhaS4T3e4Fr7D/wO+fenqVvHjq21SCjDCrt8HdVj aJ28B1SqSU2toxyg5I160GllAxEHpLFGdbFAhQfBtnmlY9eMjwmJb0sCIrkrB6XNPSPA/B2B UPISh0z2odJv35/euJF71qIFgWzp2czJHkHWwVZaZpMWWNvsLIroXoR+uA9c2V1hQFVAJZyk EE4xzfm1+oVtjIC12B9tTCuS00pY3AUy21yzNowT6SSk7HAzmtG/PJ/uSB5wEkwldB6jVs2A sjOg1wMwVvh/JHilsQg4HSmDfObmZj1d0RWlMWcUE7csRnCE0ZWBMp/ttTn+oosioGa09HAS 9jAnauznmYg43oQ5Akd8iQRxz5I58F/+JsdKvWiyrPDfYZtFS+UIgWD7x+mHBZ53Qjazszox gjwO9ehZpwUQxBm4I0lPDAKw3HJA+GwwiubTSlq5PS3P7QoCjaV8llH1bNFZMz2o8wPANiDx 5FHgpRVgwLHakoCU1Gc+LXHXBzDXt7Cj02WYHdFzMm2hXaslRdhNGowLo1SXZFXa41KGTlNe 4di53y9CK5ynV0z+YUa+5LR6RdHrHtgywdKnjeWdqhoVpsWIeORtwWGX8evNOiKJ7j0RsHha WrePTubr5nuYTDsQqgc2r4aBIOpeSRR2brlT/UE3wGgy9LY78L4EwPR0MzzecfE1Ws60iSqw Pu3vhb7h3bkCDQROsffUARAA0DrUifTrXQzqxO8aiQOC5p9Tz25Np/Tfpv1rofOwL8VPBMvJ X4P5l1V2yd70MZRUVgjmCydEyxLJ6G2YyHO2IZTEajUY0Up+b3ErOpLpZwhvgWatjifpj6bB SKuDXeThqFdkphF5kAmgfVAIkan5SxWK3+S0V2F/oxstIViBhMhDwI6XsRlnVBoLLYcEilxA 2FlRUS7MOZGmRJkRtdGD5koVZSM6xVZQSmfEBaYQ/WJBGJQdPy94nnlAVn3lH3+N7pXvNUuC GV+t4YUt3tLcRuIpYBCOWlc7bpgeCps5Xa0dIZgJ8Louu6OBJ5vVXjPxTlkFdT0S0/uerCG5 1u8p6sGRLnUeAUGkQfIUqGUjW2rHaXgWNvzOV6i3tf9YaiXKl3avFaNW1kKBs0T5M1cnlWZU Utl6k04lz5OjoNY9J/bGyV3DSlkblXRMK87iLYQSrcV6cFz9PRl4vW1LGff3xRQHngeN5fPx ze8X5NE3hb+SSwyMSEqJxhVTXJVfQWWW0dQxP7HNwqmOWYF/6m+1gK/Y2gY3jAQnsWTru4RV TZGnKwEPmOCpSUvsTRXsVHgsWJ70qd0yOSjWuiv4b8vmD3+QFgyvCBxPMdP3xsxN5etheLMO gRwWpLn6yNFq/xtgs+ECgG+gR78yXQyA7iCs5tFs2OrMqV5juSMGmn0kxJUAEQEAAYkCHwQY AQIACQUCTrH31AIbDAAKCRAgrhaS4T3e4BKwD/0ZOOmUNOZCSOLAMjZx3mtYtjYgfUNKi0ki YPveGoRWTqbis8UitPtNrG4XxgzLOijSdOEzQwkdOIp/QnZhGNssMejCnsluK0GQd+RkFVWN mcQT78hBeGcnEMAXZKq7bkIKzvc06GFmkMbX/gAl6DiNGv0UNAX+5FYh+ucCJZSyAp3sA+9/ LKjxnTedX0aygXA6rkpX0Y0FvN/9dfm47+LGq7WAqBOyYTU3E6/+Z72bZoG/cG7ANLxcPool LOrU43oqFnD8QwcN56y4VfFj3/jDF2MX3xu4v2OjglVjMEYHTCxP3mpxesGHuqOit/FR+mF0 MP9JGfj6x+bj/9JMBtCW1bY/aPeMdPGTJvXjGtOVYblGZrSjXRn5++Uuy36CvkcrjuziSDG+ JEexGxczWwN4mrOQWhMT5Jyb+18CO+CWxJfHaYXiLEW7dI1AynL4jjn4W0MSiXpWDUw+fsBO Pk6ah10C4+R1Jc7dyUsKksMfvvhRX1hTIXhth85H16706bneTayZBhlZ/hK18uqTX+s0onG/ m1F3vYvdlE4p2ts1mmixMF7KajN9/E5RQtiSArvKTbfsB6Two4MthIuLuf+M0mI4gPl9SPlf fWCYVPhaU9o83y1KFbD/+lh1pjP7bEu/YudBvz7F2Myjh4/9GUAijrCTNeDTDAgvIJDjXuLX pA== Message-ID: <924950e6-e016-25b2-4ee1-b5ea9f752c12@sandeen.net> Date: Wed, 15 Apr 2020 20:02:04 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200416005636.GA11244@42.do-not-panic.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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 4/15/20 7:56 PM, Luis Chamberlain wrote: > On Wed, Apr 15, 2020 at 12:38:26PM -0500, Eric Sandeen wrote: >> On 4/13/20 11:18 PM, Luis Chamberlain wrote: >>> On commit 6ac93117ab00 ("blktrace: use existing disk debugfs director= y") >>> merged on v4.12 Omar fixed the original blktrace code for request-bas= ed >>> drivers (multiqueue). This however left in place a possible crash, if= you >>> happen to abuse blktrace in a way it was not intended. >>> >>> Namely, if you loop adding a device, setup the blktrace with BLKTRACE= SETUP, >>> forget to BLKTRACETEARDOWN, and then just remove the device you end u= p >>> with a panic: >> >> I think this patch makes this all cleaner anyway, but - without the ap= parent >> loop bug mentioned by Bart which allows removal of the loop device whi= le blktrace >> is active (if I read that right), can this still happen? >=20 > I have not tested that, but some modifications of the break-blktrace > program could enable us to test that FWIW, I modified it to modprobe & rmmod scsi_debug instead of the loop io= ctls, and the module can't be unloaded after the blktrace is started since it's= busy. Not sure that's equivalent tho. > however I don't think the race > would be possible after patch 3/5 "blktrace: refcount the request_queue > during ioctl" is merged, as removal then a pending blktrace would > refcount the request_queue and the removal would have to wait until > the refcount is decremeneted, until after the blktrace ioctl. I'm out of my depth in the block layer, not sure who's supposed to take refs on what. ;) -Eric