From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: [PATCH] sg: Fix double-free when drives detach during SG_IO Date: Mon, 2 Nov 2015 21:57:35 +0100 Message-ID: <5637CE3F.6020706@interlog.com> References: <944215ec334c3c5b3af98210acf8f6479f5539c8.1445634103.git.calvinowens@fb.com> Reply-To: dgilbert@interlog.com Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <944215ec334c3c5b3af98210acf8f6479f5539c8.1445634103.git.calvinowens@fb.com> Sender: linux-kernel-owner@vger.kernel.org To: Calvin Owens , "James E.J. Bottomley" Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com List-Id: linux-scsi@vger.kernel.org On 15-10-31 12:57 AM, Calvin Owens wrote: > In sg_common_write(), we free the block request and return -ENODEV if > the device is detached in the middle of the SG_IO ioctl(). > > Unfortunately, sg_finish_rem_req() also tries to free srp->rq, so we > end up freeing rq->cmd in the already free rq object, and then free > the object itself out from under the current user. > > This ends up corrupting random memory via the list_head on the rq > object. The most common crash trace I saw is this: > > ------------[ cut here ]------------ > kernel BUG at block/blk-core.c:1420! > Call Trace: > [] blk_put_request+0x5b/0x80 > [] sg_finish_rem_req+0x6b/0x120 [sg] > [] sg_common_write.isra.14+0x459/0x5a0 [sg] > [] ? selinux_file_alloc_security+0x48/0x70 > [] sg_new_write.isra.17+0x195/0x2d0 [sg] > [] sg_ioctl+0x644/0xdb0 [sg] > [] do_vfs_ioctl+0x90/0x520 > [] ? file_has_perm+0x97/0xb0 > [] SyS_ioctl+0x91/0xb0 > [] tracesys+0xdd/0xe2 > RIP [] __blk_put_request+0x154/0x1a0 > > The solution is straightforward: just set srp->rq to NULL in the > failure branch so that sg_finish_rem_req() doesn't attempt to re-free > it. > > Additionally, since sg_rq_end_io() will never be called on the object > when this happens, we need to free memory backing ->cmd if it isn't > embedded in the object itself. > > KASAN was extremely helpful in finding the root cause of this bug. > > Signed-off-by: Calvin Owens Acked-by: Douglas Gilbert Thanks. > --- > drivers/scsi/sg.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c > index 9d7b7db..503ab8b 100644 > --- a/drivers/scsi/sg.c > +++ b/drivers/scsi/sg.c > @@ -787,8 +787,14 @@ sg_common_write(Sg_fd * sfp, Sg_request * srp, > return k; /* probably out of space --> ENOMEM */ > } > if (atomic_read(&sdp->detaching)) { > - if (srp->bio) > + if (srp->bio) { > + if (srp->rq->cmd != srp->rq->__cmd) > + kfree(srp->rq->cmd); > + > blk_end_request_all(srp->rq, -EIO); > + srp->rq = NULL; > + } > + > sg_finish_rem_req(srp); > return -ENODEV; > } >