From c26a43ea30c65a39d184decbc90367f8f857339f Mon Sep 17 00:00:00 2001
From: Chris Apple <14171107+cjappl@users.noreply.github.com>
Date: Fri, 31 May 2024 13:20:26 -0700
Subject: [PATCH 1/2] Fix issue where fcntl was not using last arg correctly

---
 .../lib/radsan/radsan_interceptors.cpp        | 10 +++++--
 .../radsan/tests/radsan_test_interceptors.cpp | 26 +++++++++++++++++--
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/compiler-rt/lib/radsan/radsan_interceptors.cpp b/compiler-rt/lib/radsan/radsan_interceptors.cpp
index 8acdd8504607b..1c25c8ff8c00b 100644
--- a/compiler-rt/lib/radsan/radsan_interceptors.cpp
+++ b/compiler-rt/lib/radsan/radsan_interceptors.cpp
@@ -88,10 +88,16 @@ INTERCEPTOR(int, fcntl, int filedes, int cmd, ...) {
 
   va_list args;
   va_start(args, cmd);
-  void *arg = va_arg(args, void *);
+
+  // bit of a hack here, we need to throw the argument into a variable that will
+  // hold the largest of the possible argument types. It is then assumed that
+  // fcntl will cast it properly.
+  const unsigned long arg = va_arg(args, unsigned long);
+  int result = REAL(fcntl)(filedes, cmd, arg);
+
   va_end(args);
 
-  return fcntl(filedes, cmd, arg);
+  return result;
 }
 
 INTERCEPTOR(int, close, int filedes) {
diff --git a/compiler-rt/lib/radsan/tests/radsan_test_interceptors.cpp b/compiler-rt/lib/radsan/tests/radsan_test_interceptors.cpp
index 3dabd38fec72a..b62dd7af57548 100644
--- a/compiler-rt/lib/radsan/tests/radsan_test_interceptors.cpp
+++ b/compiler-rt/lib/radsan/tests/radsan_test_interceptors.cpp
@@ -213,11 +213,11 @@ TEST(TestRadsanInterceptors, fcntlFlockDiesWhenRealtime) {
   ASSERT_THAT(fd, Ne(-1));
 
   auto func = [fd]() {
-    struct flock lock{};
+    struct flock lock {};
     lock.l_type = F_RDLCK;
     lock.l_whence = SEEK_SET;
     lock.l_start = 0;
-    lock.l_len = 0; 
+    lock.l_len = 0;
     lock.l_pid = ::getpid();
 
     ASSERT_THAT(fcntl(fd, F_GETLK, &lock), Eq(0));
@@ -230,6 +230,28 @@ TEST(TestRadsanInterceptors, fcntlFlockDiesWhenRealtime) {
   std::remove(temporary_file_path());
 }
 
+TEST(TestRadsanInterceptors, fcntlSetFdDiesWhenRealtime) {
+  int fd = creat(temporary_file_path(), S_IRUSR | S_IWUSR);
+  ASSERT_THAT(fd, Ne(-1));
+
+  auto func = [fd]() {
+    int old_flags = fcntl(fd, F_GETFD);
+    ASSERT_THAT(fcntl(fd, F_SETFD, FD_CLOEXEC), Eq(0));
+
+    int flags = fcntl(fd, F_GETFD);
+    ASSERT_THAT(flags, Ne(-1));
+    ASSERT_THAT(flags & FD_CLOEXEC, Eq(FD_CLOEXEC));
+
+    ASSERT_THAT(fcntl(fd, F_SETFD, old_flags), Eq(0));
+    ASSERT_THAT(fcntl(fd, F_GETFD), Eq(old_flags));
+  };
+
+  expectRealtimeDeath(func, "fcntl");
+  expectNonrealtimeSurvival(func);
+
+  close(fd);
+}
+
 TEST(TestRadsanInterceptors, closeDiesWhenRealtime) {
   auto func = []() { close(0); };
   expectRealtimeDeath(func, "close");

From 47e935032f791b2956b6cfb6873cd33af5a1854e Mon Sep 17 00:00:00 2001
From: Chris Apple <14171107+cjappl@users.noreply.github.com>
Date: Fri, 31 May 2024 14:11:53 -0700
Subject: [PATCH 2/2] Comment update

---
 compiler-rt/lib/radsan/radsan_interceptors.cpp | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/compiler-rt/lib/radsan/radsan_interceptors.cpp b/compiler-rt/lib/radsan/radsan_interceptors.cpp
index 1c25c8ff8c00b..2ff174d5118fc 100644
--- a/compiler-rt/lib/radsan/radsan_interceptors.cpp
+++ b/compiler-rt/lib/radsan/radsan_interceptors.cpp
@@ -89,9 +89,13 @@ INTERCEPTOR(int, fcntl, int filedes, int cmd, ...) {
   va_list args;
   va_start(args, cmd);
 
-  // bit of a hack here, we need to throw the argument into a variable that will
-  // hold the largest of the possible argument types. It is then assumed that
-  // fcntl will cast it properly.
+  // Following precedent here. The linux source (fcntl.c, do_fcntl) accepts the
+  // final argument in a variable that will hold the largest of the possible
+  // argument types (pointers and ints are typical in fcntl) It is then assumed
+  // that the implementation of fcntl will cast it properly depending on cmd.
+  //
+  // This is also similar to what is done in
+  // sanitizer_common/sanitizer_common_syscalls.inc
   const unsigned long arg = va_arg(args, unsigned long);
   int result = REAL(fcntl)(filedes, cmd, arg);