From: Dan Minor <dminor@mozilla.com>
Date: Wed, 8 Jul 2020 17:35:00 +0000
Subject: Bug 1650572 - Check V4L2_CAP_DEVICE_CAPS before accessing
 device_caps; r=ng

The capabilities field is for the physical device, device_caps is for the
specific /dev/videoX device that has been opened. The device_caps field is
only populated if V4L2_CAP_DEVICE_CAPS is set, so we should check that, and
fall back to capabilities if it is not set.

Differential Revision: https://phabricator.services.mozilla.com/D82377
Mercurial Revision: https://hg.mozilla.org/mozilla-central/rev/b5acbf536c46a66c939a61bde34ad93b1977a604
---
 modules/video_capture/linux/device_info_v4l2.cc | 17 ++++++++++++-----
 modules/video_capture/linux/device_info_v4l2.h  |  3 +++
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/modules/video_capture/linux/device_info_v4l2.cc b/modules/video_capture/linux/device_info_v4l2.cc
index a2435bcd4f..cd0ba6e3df 100644
--- a/modules/video_capture/linux/device_info_v4l2.cc
+++ b/modules/video_capture/linux/device_info_v4l2.cc
@@ -220,8 +220,7 @@ uint32_t DeviceInfoV4l2::NumberOfDevices() {
     snprintf(device, sizeof(device), "/dev/video%d", n);
     if ((fd = open(device, O_RDONLY)) != -1) {
       // query device capabilities and make sure this is a video capture device
-      if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0 ||
-          !(cap.device_caps & V4L2_CAP_VIDEO_CAPTURE)) {
+      if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0 || !IsVideoCaptureDevice(&cap)) {
         close(fd);
         continue;
       }
@@ -252,8 +251,7 @@ int32_t DeviceInfoV4l2::GetDeviceName(uint32_t deviceNumber,
     snprintf(device, sizeof(device), "/dev/video%d", n);
     if ((fd = open(device, O_RDONLY)) != -1) {
       // query device capabilities and make sure this is a video capture device
-      if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0 ||
-          !(cap.device_caps & V4L2_CAP_VIDEO_CAPTURE)) {
+      if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0 || !IsVideoCaptureDevice(&cap)) {
         close(fd);
         continue;
       }
@@ -331,7 +329,7 @@ int32_t DeviceInfoV4l2::CreateCapabilityMap(const char* deviceUniqueIdUTF8) {
     struct v4l2_capability cap;
     if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == 0) {
       // skip devices without video capture capability
-      if (!(cap.device_caps & V4L2_CAP_VIDEO_CAPTURE)) {
+      if (!IsVideoCaptureDevice(&cap)) {
         continue;
       }
 
@@ -393,6 +391,15 @@ bool DeviceInfoV4l2::IsDeviceNameMatches(const char* name,
   return false;
 }
 
+bool DeviceInfoV4l2::IsVideoCaptureDevice(struct v4l2_capability* cap)
+{
+  if (cap->capabilities & V4L2_CAP_DEVICE_CAPS) {
+    return cap->device_caps & V4L2_CAP_VIDEO_CAPTURE;
+  } else {
+    return cap->capabilities & V4L2_CAP_VIDEO_CAPTURE;
+  }
+}
+
 int32_t DeviceInfoV4l2::FillCapabilities(int fd) {
   // set image format
   struct v4l2_format video_fmt;
diff --git a/modules/video_capture/linux/device_info_v4l2.h b/modules/video_capture/linux/device_info_v4l2.h
index 95432a509d..e3c2395f49 100644
--- a/modules/video_capture/linux/device_info_v4l2.h
+++ b/modules/video_capture/linux/device_info_v4l2.h
@@ -18,6 +18,8 @@
 #include "rtc_base/platform_thread.h"
 #include <sys/inotify.h>
 
+struct v4l2_capability;
+
 namespace webrtc {
 namespace videocapturemodule {
 class DeviceInfoV4l2 : public DeviceInfoImpl {
@@ -49,6 +51,7 @@ class DeviceInfoV4l2 : public DeviceInfoImpl {
 
  private:
   bool IsDeviceNameMatches(const char* name, const char* deviceUniqueIdUTF8);
+  bool IsVideoCaptureDevice(struct v4l2_capability* cap);
 
 #ifdef WEBRTC_LINUX
   void HandleEvent(inotify_event* event, int fd);