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[76.204.101.112]) by smtp.gmail.com with ESMTPSA id 00721157ae682-81f33c2df04sm21047067b3.12.2026.07.22.17.02.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jul 2026 17:02:17 -0700 (PDT) From: "Cen Zhang (Microsoft)" To: mchehab@kernel.org, hverkuil@kernel.org Cc: kees@kernel.org, rongqianfeng@vivo.com, axboe@kernel.dk, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, AutonomousCodeSecurity@microsoft.com, tgopinath@linux.microsoft.com, kys@microsoft.com, blbllhy@gmail.com, stable@vger.kernel.org Subject: [PATCH] media: dvb-core: fix race between dvb_dvr_read() and dvb_dvr_set_buffer_size() Date: Wed, 22 Jul 2026 20:00:16 -0400 Message-ID: <20260723000016.84091-1-blbllhy@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" dvb_dvr_read() accesses the DVR ring buffer without holding dmxdev->mutex, while ioctl(DMX_SET_BUFFER_SIZE) replaces the backing memory of the buffer under that mutex. A concurrent resize can free the vmalloc region while the reader is still copying from it, resulting in a use-after-free read. BUG: KASAN: vmalloc-out-of-bounds in _copy_to_user+0x4e/0x80 _copy_to_user+0x4e/0x80 dvb_ringbuffer_read_user+0x141/0x390 (dvb_ringbuffer.c:151) dvb_dmxdev_buffer_read.isra.0+0x310/0x3e0 dvb_dvr_read+0xc6/0x110 vfs_read+0x1ac/0x940 This is a re-discovery of an issue noted by the original author: https://lore.kernel.org/all/47E45138.1030107@googlemail.com/. Fix by protecting dvb_dvr_read() with dmxdev->mutex. Fixes: a095be4b030c ("V4L/DVB (7659): dvb-core: Implement DMX_SET_BUFFER_SI= ZE for dvr") Cc: stable@vger.kernel.org Reported-by: AutonomousCodeSecurity@microsoft.com Signed-off-by: Cen Zhang (Microsoft) --- drivers/media/dvb-core/dmxdev.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/drivers/media/dvb-core/dmxdev.c b/drivers/media/dvb-core/dmxde= v.c index 3c8bc75e4d6c..b4aa8d37ff03 100644 --- a/drivers/media/dvb-core/dmxdev.c +++ b/drivers/media/dvb-core/dmxdev.c @@ -270,13 +270,23 @@ static ssize_t dvb_dvr_read(struct file *file, char _= _user *buf, size_t count, { struct dvb_device *dvbdev =3D file->private_data; struct dmxdev *dmxdev =3D dvbdev->priv; + ssize_t ret; =20 - if (dmxdev->exit) + if (mutex_lock_interruptible(&dmxdev->mutex)) + return -ERESTARTSYS; + + if (dmxdev->exit) { + mutex_unlock(&dmxdev->mutex); return -ENODEV; + } + + ret =3D dvb_dmxdev_buffer_read(&dmxdev->dvr_buffer, + file->f_flags & O_NONBLOCK, + buf, count, ppos); =20 - return dvb_dmxdev_buffer_read(&dmxdev->dvr_buffer, - file->f_flags & O_NONBLOCK, - buf, count, ppos); + mutex_unlock(&dmxdev->mutex); + + return ret; } =20 static int dvb_dvr_set_buffer_size(struct dmxdev *dmxdev, --=20 2.53.0