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Sat, 02 Nov 2019 13:50:11 -0700 (PDT) Reply-To: alex.popov@linux.com Subject: Re: [PATCH v3 1/1] media: vivid: Fix wrong locking that causes race conditions on streaming stop To: Linus Torvalds , Hans Verkuil , Mauro Carvalho Chehab , Security Officers , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org References: <20191102190327.24903-1-alex.popov@linux.com> From: Alexander Popov Autocrypt: addr=alex.popov@linux.com; prefer-encrypt=mutual; keydata= mQINBFX15q4BEADZartsIW3sQ9R+9TOuCFRIW+RDCoBWNHhqDLu+Tzf2mZevVSF0D5AMJW4f UB1QigxOuGIeSngfmgLspdYe2Kl8+P8qyfrnBcS4hLFyLGjaP7UVGtpUl7CUxz2Hct3yhsPz ID/rnCSd0Q+3thrJTq44b2kIKqM1swt/F2Er5Bl0B4o5WKx4J9k6Dz7bAMjKD8pHZJnScoP4 dzKPhrytN/iWM01eRZRc1TcIdVsRZC3hcVE6OtFoamaYmePDwWTRhmDtWYngbRDVGe3Tl8bT 7BYN7gv7Ikt7Nq2T2TOfXEQqr9CtidxBNsqFEaajbFvpLDpUPw692+4lUbQ7FL0B1WYLvWkG cVysClEyX3VBSMzIG5eTF0Dng9RqItUxpbD317ihKqYL95jk6eK6XyI8wVOCEa1V3MhtvzUo WGZVkwm9eMVZ05GbhzmT7KHBEBbCkihS+TpVxOgzvuV+heCEaaxIDWY/k8u4tgbrVVk+tIVG 99v1//kNLqd5KuwY1Y2/h2MhRrfxqGz+l/f/qghKh+1iptm6McN//1nNaIbzXQ2Ej34jeWDa xAN1C1OANOyV7mYuYPNDl5c9QrbcNGg3D6gOeGeGiMn11NjbjHae3ipH8MkX7/k8pH5q4Lhh Ra0vtJspeg77CS4b7+WC5jlK3UAKoUja3kGgkCrnfNkvKjrkEwARAQABtCZBbGV4YW5kZXIg UG9wb3YgPGFsZXgucG9wb3ZAbGludXguY29tPokCVwQTAQgAQQIbIwIeAQIXgAULCQgHAwUV CgkICwUWAgMBAAIZARYhBLl2JLAkAVM0bVvWTo4Oneu8fo+qBQJdehKcBQkLRpLuAAoJEI4O neu8fo+qrkgP/jS0EhDnWhIFBnWaUKYWeiwR69DPwCs/lNezOu63vg30O9BViEkWsWwXQA+c SVVTz5f9eB9K2me7G06A3U5AblOJKdoZeNX5GWMdrrGNLVISsa0geXNT95TRnFqE1HOZJiHT NFyw2nv+qQBUHBAKPlk3eL4/Yev/P8w990Aiiv6/RN3IoxqTfSu2tBKdQqdxTjEJ7KLBlQBm 5oMpm/P2Y/gtBiXRvBd7xgv7Y3nShPUDymjBnc+efHFqARw84VQPIG4nqVhIei8gSWps49DX kp6v4wUzUAqFo+eh/ErWmyBNETuufpxZnAljtnKpwmpFCcq9yfcMlyOO9/viKn14grabE7qE 4j3/E60wraHu8uiXJlfXmt0vG16vXb8g5a25Ck09UKkXRGkNTylXsAmRbrBrA3Moqf8QzIk9 p+aVu/vFUs4ywQrFNvn7Qwt2hWctastQJcH3jrrLk7oGLvue5KOThip0SNicnOxVhCqstjYx KEnzZxtna5+rYRg22Zbfg0sCAAEGOWFXjqg3hw400oRxTW7IhiE34Kz1wHQqNif0i5Eor+TS 22r9iF4jUSnk1jaVeRKOXY89KxzxWhnA06m8IvW1VySHoY1ZG6xEZLmbp3OuuFCbleaW07OU 9L8L1Gh1rkAz0Fc9eOR8a2HLVFnemmgAYTJqBks/sB/DD0SuuQINBFX15q4BEACtxRV/pF1P XiGSbTNPlM9z/cElzo/ICCFX+IKg+byRvOMoEgrzQ28ah0N5RXQydBtfjSOMV1IjSb3oc23z oW2J9DefC5b8G1Lx2Tz6VqRFXC5OAxuElaZeoowV1VEJuN3Ittlal0+KnRYY0PqnmLzTXGA9 GYjw/p7l7iME7gLHVOggXIk7MP+O+1tSEf23n+dopQZrkEP2BKSC6ihdU4W8928pApxrX1Lt tv2HOPJKHrcfiqVuFSsb/skaFf4uveAPC4AausUhXQVpXIg8ZnxTZ+MsqlwELv+Vkm/SNEWl n0KMd58gvG3s0bE8H2GTaIO3a0TqNKUY16WgNglRUi0WYb7+CLNrYqteYMQUqX7+bB+NEj/4 8dHw+xxaIHtLXOGxW6zcPGFszaYArjGaYfiTTA1+AKWHRKvD3MJTYIonphy5EuL9EACLKjEF v3CdK5BLkqTGhPfYtE3B/Ix3CUS1Aala0L+8EjXdclVpvHQ5qXHs229EJxfUVf2ucpWNIUdf lgnjyF4B3R3BFWbM4Yv8QbLBvVv1Dc4hZ70QUXy2ZZX8keza2EzPj3apMcDmmbklSwdC5kYG EFT4ap06R2QW+6Nw27jDtbK4QhMEUCHmoOIaS9j0VTU4fR9ZCpVT/ksc2LPMhg3YqNTrnb1v RVNUZvh78zQeCXC2VamSl9DMcwARAQABiQI8BBgBCAAmAhsMFiEEuXYksCQBUzRtW9ZOjg6d 67x+j6oFAl16ErcFCQtGkwkACgkQjg6d67x+j6q7zA/+IsjSKSJypgOImN9LYjeb++7wDjXp qvEpq56oAn21CvtbGus3OcC0hrRtyZ/rC5Qc+S5SPaMRFUaK8S3j1vYC0wZJ99rrmQbcbYMh C2o0k4pSejaINmgyCajVOhUhln4IuwvZke1CLfXe1i3ZtlaIUrxfXqfYpeijfM/JSmliPxwW BRnQRcgS85xpC1pBUMrraxajaVPwu7hCTke03v6bu8zSZlgA1rd9E6KHu2VNS46VzUPjbR77 kO7u6H5PgQPKcuJwQQ+d3qa+5ZeKmoVkc2SuHVrCd1yKtAMmKBoJtSku1evXPwyBzqHFOInk mLMtrWuUhj+wtcnOWxaP+n4ODgUwc/uvyuamo0L2Gp3V5ItdIUDO/7ZpZ/3JxvERF3Yc1md8 5kfflpLzpxyl2fKaRdvxr48ZLv9XLUQ4qNuADDmJArq/+foORAX4BBFWvqZQKe8a9ZMAvGSh uoGUVg4Ks0uC4IeG7iNtd+csmBj5dNf91C7zV4bsKt0JjiJ9a4D85dtCOPmOeNuusK7xaDZc gzBW8J8RW+nUJcTpudX4TC2SGeAOyxnM5O4XJ8yZyDUY334seDRJWtS4wRHxpfYcHKTewR96 IsP1USE+9ndu6lrMXQ3aFsd1n1m1pfa/y8hiqsSYHy7JQ9Iuo9DxysOj22UNOmOE+OYPK48D j3lCqPk= Message-ID: <8edf1056-072d-9718-74ac-e6b8c0339228@linux.com> Date: Sat, 2 Nov 2019 23:50:08 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191102190327.24903-1-alex.popov@linux.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I've announced this patch at the oss-security ML: https://www.openwall.com/lists/oss-security/2019/11/02/1 Best regards, Alexander On 02.11.2019 22:03, Alexander Popov wrote: > There is the same incorrect approach to locking implemented in > vivid_stop_generating_vid_cap(), vivid_stop_generating_vid_out() and > sdr_cap_stop_streaming(). > > These functions are called during streaming stopping with vivid_dev.mutex > locked. And they all do the same mistake while stopping their kthreads, > which need to lock this mutex as well. See the example from > vivid_stop_generating_vid_cap(): > /* shutdown control thread */ > vivid_grab_controls(dev, false); > mutex_unlock(&dev->mutex); > kthread_stop(dev->kthread_vid_cap); > dev->kthread_vid_cap = NULL; > mutex_lock(&dev->mutex); > > But when this mutex is unlocked, another vb2_fop_read() can lock it > instead of vivid_thread_vid_cap() and manipulate the buffer queue. > That causes a use-after-free access later. > > To fix those issues let's: > 1. avoid unlocking the mutex in vivid_stop_generating_vid_cap(), > vivid_stop_generating_vid_out() and sdr_cap_stop_streaming(); > 2. use mutex_trylock() with schedule_timeout() in the loops > of the vivid kthread handlers. > > Signed-off-by: Alexander Popov > Acked-by: Linus Torvalds > --- > drivers/media/platform/vivid/vivid-kthread-cap.c | 8 +++++--- > drivers/media/platform/vivid/vivid-kthread-out.c | 8 +++++--- > drivers/media/platform/vivid/vivid-sdr-cap.c | 8 +++++--- > 3 files changed, 15 insertions(+), 9 deletions(-) > > diff --git a/drivers/media/platform/vivid/vivid-kthread-cap.c b/drivers/media/platform/vivid/vivid-kthread-cap.c > index 003319d7816d..27b9c78d2d05 100644 > --- a/drivers/media/platform/vivid/vivid-kthread-cap.c > +++ b/drivers/media/platform/vivid/vivid-kthread-cap.c > @@ -796,7 +796,11 @@ static int vivid_thread_vid_cap(void *data) > if (kthread_should_stop()) > break; > > - mutex_lock(&dev->mutex); > + if (!mutex_trylock(&dev->mutex)) { > + schedule_timeout(1); > + continue; > + } > + > cur_jiffies = jiffies; > if (dev->cap_seq_resync) { > dev->jiffies_vid_cap = cur_jiffies; > @@ -956,8 +960,6 @@ void vivid_stop_generating_vid_cap(struct vivid_dev *dev, bool *pstreaming) > > /* shutdown control thread */ > vivid_grab_controls(dev, false); > - mutex_unlock(&dev->mutex); > kthread_stop(dev->kthread_vid_cap); > dev->kthread_vid_cap = NULL; > - mutex_lock(&dev->mutex); > } > diff --git a/drivers/media/platform/vivid/vivid-kthread-out.c b/drivers/media/platform/vivid/vivid-kthread-out.c > index ce5bcda2348c..a657b0d20e2f 100644 > --- a/drivers/media/platform/vivid/vivid-kthread-out.c > +++ b/drivers/media/platform/vivid/vivid-kthread-out.c > @@ -143,7 +143,11 @@ static int vivid_thread_vid_out(void *data) > if (kthread_should_stop()) > break; > > - mutex_lock(&dev->mutex); > + if (!mutex_trylock(&dev->mutex)) { > + schedule_timeout(1); > + continue; > + } > + > cur_jiffies = jiffies; > if (dev->out_seq_resync) { > dev->jiffies_vid_out = cur_jiffies; > @@ -301,8 +305,6 @@ void vivid_stop_generating_vid_out(struct vivid_dev *dev, bool *pstreaming) > > /* shutdown control thread */ > vivid_grab_controls(dev, false); > - mutex_unlock(&dev->mutex); > kthread_stop(dev->kthread_vid_out); > dev->kthread_vid_out = NULL; > - mutex_lock(&dev->mutex); > } > diff --git a/drivers/media/platform/vivid/vivid-sdr-cap.c b/drivers/media/platform/vivid/vivid-sdr-cap.c > index 9acc709b0740..590080716962 100644 > --- a/drivers/media/platform/vivid/vivid-sdr-cap.c > +++ b/drivers/media/platform/vivid/vivid-sdr-cap.c > @@ -141,7 +141,11 @@ static int vivid_thread_sdr_cap(void *data) > if (kthread_should_stop()) > break; > > - mutex_lock(&dev->mutex); > + if (!mutex_trylock(&dev->mutex)) { > + schedule_timeout(1); > + continue; > + } > + > cur_jiffies = jiffies; > if (dev->sdr_cap_seq_resync) { > dev->jiffies_sdr_cap = cur_jiffies; > @@ -303,10 +307,8 @@ static void sdr_cap_stop_streaming(struct vb2_queue *vq) > } > > /* shutdown control thread */ > - mutex_unlock(&dev->mutex); > kthread_stop(dev->kthread_sdr_cap); > dev->kthread_sdr_cap = NULL; > - mutex_lock(&dev->mutex); > } > > static void sdr_cap_buf_request_complete(struct vb2_buffer *vb) >