From 1dcf202ffe88a6de007f1331808680576fcc955d Mon Sep 17 00:00:00 2001
From: Guillaume Petit <guillaume.petit@shadow.tech>
Date: Thu, 14 Nov 2024 15:28:03 +0100
Subject: [PATCH] Fixes a linear interpolation bad access
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Bug: webrtc:353425611
Change-Id: I9c38428d2463d9d76047ad5be84ed57cba9ebb72
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/367981
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43408}
---
 AUTHORS                                       |  1 +
 rtc_base/experiments/encoder_info_settings.cc |  6 +++
 .../encoder_info_settings_unittest.cc         | 45 +++++++++++++++++++
 3 files changed, 52 insertions(+)

diff --git a/AUTHORS b/AUTHORS
index 9424a61de1..f4dd64134d 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -56,6 +56,7 @@ Frederik Riedel, Frogg GmbH <frederik.riedel@frogg.io>
 Gao Chun <gaochun.dev@gmail.com>
 Giji Gangadharan <giji.g@samsung.com>
 Graham Yoakum <gyoakum@skobalt.com>
+Guillaume Petit <guillaume.petit@shadow.tech>
 Gustavo Garcia <gustavogb@gmail.com>
 Hans Knoechel <hans@hans-knoechel.de>
 Helmut Januschka <helmut@januschka.com>
diff --git a/rtc_base/experiments/encoder_info_settings.cc b/rtc_base/experiments/encoder_info_settings.cc
index 82480ea298..eabf8b182d 100644
--- a/rtc_base/experiments/encoder_info_settings.cc
+++ b/rtc_base/experiments/encoder_info_settings.cc
@@ -144,6 +144,12 @@ EncoderInfoSettings::GetSinglecastBitrateLimitForResolutionWhenQpIsUntrusted(
     return bitrate_limits[interpolation_index];
   }
 
+  // 0 means our resolution is smaller than the smallest resolution in the list,
+  // we will select smallest data as the return result.
+  if (interpolation_index == 0) {
+    return *bitrate_limits.begin();
+  }
+
   // No matching resolution, do a linear interpolate.
   int lower_pixel_count =
       bitrate_limits[interpolation_index - 1].frame_size_pixels;
diff --git a/rtc_base/experiments/encoder_info_settings_unittest.cc b/rtc_base/experiments/encoder_info_settings_unittest.cc
index 916f980ebe..70c0b7f0ba 100644
--- a/rtc_base/experiments/encoder_info_settings_unittest.cc
+++ b/rtc_base/experiments/encoder_info_settings_unittest.cc
@@ -103,4 +103,49 @@ TEST(EncoderSettingsTest, CommonSettingsUsedIfEncoderNameUnspecified) {
   EXPECT_EQ(3u, vp9_settings.requested_resolution_alignment());
 }
 
+TEST(GetSinglecastBitrateLimitForResolutionWhenQpIsUntrustedTests,
+     LinearInterpolationUnderflow) {
+  std::optional<int> frame_size_pixels = 480 * 360;
+  std::vector<VideoEncoder::ResolutionBitrateLimits> resolution_bitrate_limits(
+      {{1280 * 720, 1500000, 30000, 2500000},
+       {1920 * 1080, 2500000, 30000, 4000000}});
+
+  const auto resolutionBitrateLimit = EncoderInfoSettings::
+      GetSinglecastBitrateLimitForResolutionWhenQpIsUntrusted(
+          frame_size_pixels, resolution_bitrate_limits);
+  EXPECT_TRUE(resolutionBitrateLimit.has_value());
+  EXPECT_EQ(resolutionBitrateLimit.value(), resolution_bitrate_limits.front());
+}
+
+TEST(GetSinglecastBitrateLimitForResolutionWhenQpIsUntrustedTests,
+     LinearInterpolationOverflow) {
+  std::optional<int> frame_size_pixels = 4096 * 2160;
+  std::vector<VideoEncoder::ResolutionBitrateLimits> resolution_bitrate_limits(
+      {{1280 * 720, 1500000, 30000, 2500000},
+       {1920 * 1080, 2500000, 30000, 4000000}});
+
+  const auto resolutionBitrateLimit = EncoderInfoSettings::
+      GetSinglecastBitrateLimitForResolutionWhenQpIsUntrusted(
+          frame_size_pixels, resolution_bitrate_limits);
+  EXPECT_TRUE(resolutionBitrateLimit.has_value());
+  EXPECT_EQ(resolutionBitrateLimit.value(), resolution_bitrate_limits.back());
+}
+
+TEST(GetSinglecastBitrateLimitForResolutionWhenQpIsUntrustedTests,
+     LinearInterpolationExactMatch) {
+  std::optional<int> frame_size_pixels = 1920 * 1080;
+  VideoEncoder::ResolutionBitrateLimits expected_match{1920 * 1080, 2500000,
+                                                       30000, 4000000};
+  std::vector<VideoEncoder::ResolutionBitrateLimits> resolution_bitrate_limits(
+      {{1280 * 720, 1500000, 30000, 2500000},
+       expected_match,
+       {4096 * 2160, 4000000, 30000, 8000000}});
+
+  const auto resolutionBitrateLimit = EncoderInfoSettings::
+      GetSinglecastBitrateLimitForResolutionWhenQpIsUntrusted(
+          frame_size_pixels, resolution_bitrate_limits);
+  EXPECT_TRUE(resolutionBitrateLimit.has_value());
+  EXPECT_EQ(resolutionBitrateLimit.value(), expected_match);
+}
+
 }  // namespace webrtc