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Thu, 24 Sep 2026 18:07:35 -0700 (PDT) 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 Date: Fri, 25 Sep 2026 10:07:33 +0900 Message-Id: To: "Nick Rogers" Cc: "Mauro Carvalho Chehab" , "Hans Verkuil" , "Brian Daniels" , , Subject: Re: [PATCH] media: v4l2-ioctl: zero the ext control built for VIDIOC_{G,S}_CTRL From: "Alexandre Courbot" References: <20260923160936.33445-1-nick@getfieldwork.ai> In-Reply-To: <20260923160936.33445-1-nick@getfieldwork.ai> On Thu Sep 24, 2026 at 1:09 AM JST, Nick Rogers wrote: > When a driver implements the extended control ioctls but has no control > handler, v4l_g_ctrl() and v4l_s_ctrl() pass VIDIOC_G_CTRL and > VIDIOC_S_CTRL on as a single struct v4l2_ext_control built on the stack. > Only its id and value are set, and check_ext_ctrls() clears reserved[0] > and reserved2[0]; the control's size and the rest of both structures are > left uninitialized. > > A driver that forwards the controls rather than handling them through > the control framework sees that stack garbage. The virtio-media driver > under review takes a nonzero size as a payload to copy from userspace, > so VIDIOC_G_CTRL and VIDIOC_S_CTRL fail with -EINVAL through it whenever > the stack is dirty. GStreamer's V4L2 encoders set their profile with > VIDIOC_S_CTRL, and cannot negotiate against such a device. > > Zero-initialize both structures. > > Assisted-by: Claude:claude-opus-5-5 nit: per the kernel guidelines [1], this should be Assisted-by: LLM [1] https://docs.kernel.org/process/coding-assistants.html#attribution