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[217.87.94.241]) by smtp.gmail.com with ESMTPSA id b8sm7649377wrx.15.2021.05.14.12.23.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 May 2021 12:23:41 -0700 (PDT) Subject: Re: [PATCH] fdc: check drive block device before usage (CVE-2021-20196) To: P J P , John Snow , Max Reitz , Kevin Wolf , Qemu-block References: <20210123100345.642933-1-ppandit@redhat.com> From: Thomas Huth Message-ID: <6881ef3c-99a1-1f5f-cca5-0850ec2bd6cf@redhat.com> Date: Fri, 14 May 2021 21:23:39 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: <20210123100345.642933-1-ppandit@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-stable@nongnu.org, Gaoning Pan , QEMU Developers , Prasad J Pandit Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 23/01/2021 11.03, P J P wrote: > From: Prasad J Pandit > > While processing ioport command in 'fdctrl_write_dor', device > controller may select a drive which is not initialised with a > block device. This may result in a NULL pointer dereference. > Add checks to avoid it. > > Fixes: CVE-2021-20196 > Reported-by: Gaoning Pan > Buglink: https://bugs.launchpad.net/qemu/+bug/1912780 > Signed-off-by: Prasad J Pandit > --- > hw/block/fdc.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > diff --git a/hw/block/fdc.c b/hw/block/fdc.c > index 3636874432..13a9470d19 100644 > --- a/hw/block/fdc.c > +++ b/hw/block/fdc.c > @@ -1429,7 +1429,9 @@ static void fdctrl_write_dor(FDCtrl *fdctrl, uint32_t value) > } > } > /* Selected drive */ > - fdctrl->cur_drv = value & FD_DOR_SELMASK; > + if (fdctrl->drives[value & FD_DOR_SELMASK].blk) { > + fdctrl->cur_drv = value & FD_DOR_SELMASK; > + } > > fdctrl->dor = value; > } > @@ -1894,6 +1896,10 @@ static uint32_t fdctrl_read_data(FDCtrl *fdctrl) > uint32_t pos; > > cur_drv = get_cur_drv(fdctrl); > + if (!cur_drv->blk) { > + FLOPPY_DPRINTF("No drive connected\n"); > + return 0; > + } > fdctrl->dsr &= ~FD_DSR_PWRDOWN; > if (!(fdctrl->msr & FD_MSR_RQM) || !(fdctrl->msr & FD_MSR_DIO)) { > FLOPPY_DPRINTF("error: controller not ready for reading\n"); > @@ -2420,7 +2426,8 @@ static void fdctrl_write_data(FDCtrl *fdctrl, uint32_t value) > if (pos == FD_SECTOR_LEN - 1 || > fdctrl->data_pos == fdctrl->data_len) { > cur_drv = get_cur_drv(fdctrl); > - if (blk_pwrite(cur_drv->blk, fd_offset(cur_drv), fdctrl->fifo, > + if (cur_drv->blk == NULL > + || blk_pwrite(cur_drv->blk, fd_offset(cur_drv), fdctrl->fifo, > BDRV_SECTOR_SIZE, 0) < 0) { > FLOPPY_DPRINTF("error writing sector %d\n", > fd_sector(cur_drv)); > Ping again! Could anybody review / pick this up? Thomas