From e352e896cb854759a2991b9f86389d7b01cf52a1 Mon Sep 17 00:00:00 2001
From: Yijie Ma <yijiem@google.com>
Date: Thu, 14 Nov 2024 12:07:29 -0800
Subject: [PATCH] [c-ares] Fix inverted length check in GrpcPolledFdWindows
 (#38101)

Fix https://github.com/grpc/grpc/issues/37969.

There is an inverted length check in GrpcPolledFdWindows before memcpying from gRPC's `recv_from_source_addr_` into c-ares' socket address structure. In newer c-ares version, it changed to use `struct sockaddr_storage` for the socket address which is 128 bytes and hit this issue.

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Closes #38101

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/38101 from yijiem:37969 282fc8269e4a65625463e0e64d7ee80e3b3216ea
PiperOrigin-RevId: 696607100
---
 src/core/lib/event_engine/windows/grpc_polled_fd_windows.cc | 2 +-
 src/core/resolver/dns/c_ares/grpc_ares_ev_driver_windows.cc | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/core/lib/event_engine/windows/grpc_polled_fd_windows.cc b/src/core/lib/event_engine/windows/grpc_polled_fd_windows.cc
index 3bfd15537e61b..0d4dcd5579ef4 100644
--- a/src/core/lib/event_engine/windows/grpc_polled_fd_windows.cc
+++ b/src/core/lib/event_engine/windows/grpc_polled_fd_windows.cc
@@ -224,7 +224,7 @@ class GrpcPolledFdWindows : public GrpcPolledFd {
     // c-ares overloads this recv_from virtual socket function to receive
     // data on both UDP and TCP sockets, and from is nullptr for TCP.
     if (from != nullptr) {
-      CHECK(*from_len <= recv_from_source_addr_len_);
+      CHECK(*from_len >= recv_from_source_addr_len_);
       memcpy(from, &recv_from_source_addr_, recv_from_source_addr_len_);
       *from_len = recv_from_source_addr_len_;
     }
diff --git a/src/core/resolver/dns/c_ares/grpc_ares_ev_driver_windows.cc b/src/core/resolver/dns/c_ares/grpc_ares_ev_driver_windows.cc
index 6f988c8710db4..f30826bbb43dc 100644
--- a/src/core/resolver/dns/c_ares/grpc_ares_ev_driver_windows.cc
+++ b/src/core/resolver/dns/c_ares/grpc_ares_ev_driver_windows.cc
@@ -307,7 +307,7 @@ class GrpcPolledFdWindows final : public GrpcPolledFd {
     // c-ares overloads this recv_from virtual socket function to receive
     // data on both UDP and TCP sockets, and from is nullptr for TCP.
     if (from != nullptr) {
-      CHECK(*from_len <= recv_from_source_addr_len_);
+      CHECK(*from_len >= recv_from_source_addr_len_);
       memcpy(from, &recv_from_source_addr_, recv_from_source_addr_len_);
       *from_len = recv_from_source_addr_len_;
     }