[compiler-rt] [rtsan] Fix va_args handling in open functions (PR #108291)

[Chris Apple via llvm-commits]

https://github.com/cjappl created https://github.com/llvm/llvm-project/pull/108291

It is only valid to read from the variadic parameter if O_CREAT is specified in the input flags, otherwise we should pass nothing in.

>From 1363f42967ea729026fbccdbadd63ea1916bb002 Mon Sep 17 00:00:00 2001
From: Chris Apple <cja-private at pm.me>
Date: Wed, 11 Sep 2024 14:41:14 -0600
Subject: [PATCH] [rtsan] Fix va_args handling in open functions

---
 compiler-rt/lib/rtsan/rtsan_interceptors.cpp | 28 +++++++++++---------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/compiler-rt/lib/rtsan/rtsan_interceptors.cpp b/compiler-rt/lib/rtsan/rtsan_interceptors.cpp
index 409e27c3ad3234..a9398cf284d827 100644
--- a/compiler-rt/lib/rtsan/rtsan_interceptors.cpp
+++ b/compiler-rt/lib/rtsan/rtsan_interceptors.cpp
@@ -64,13 +64,15 @@ INTERCEPTOR(int, open, const char *path, int oflag, ...) {
   // O_NONBLOCK
   __rtsan_expect_not_realtime("open");
 
-  va_list args;
-  va_start(args, oflag);
-  const mode_t mode = va_arg(args, int);
-  va_end(args);
+  if (oflag & O_CREAT) {
+    va_list args;
+    va_start(args, oflag);
+    const mode_t mode = va_arg(args, int);
+    va_end(args);
+    return REAL(open)(path, oflag, mode);
+  }
 
-  const int result = REAL(open)(path, oflag, mode);
-  return result;
+  return REAL(open)(path, oflag);
 }
 
 INTERCEPTOR(int, openat, int fd, const char *path, int oflag, ...) {
@@ -78,13 +80,15 @@ INTERCEPTOR(int, openat, int fd, const char *path, int oflag, ...) {
   // O_NONBLOCK
   __rtsan_expect_not_realtime("openat");
 
-  va_list args;
-  va_start(args, oflag);
-  mode_t mode = va_arg(args, int);
-  va_end(args);
+  if (oflag & O_CREAT) {
+    va_list args;
+    va_start(args, oflag);
+    const mode_t mode = va_arg(args, int);
+    va_end(args);
+    return REAL(openat)(fd, path, oflag, mode);
+  }
 
-  const int result = REAL(openat)(fd, path, oflag, mode);
-  return result;
+  return REAL(openat)(fd, path, oflag);
 }
 
 INTERCEPTOR(int, creat, const char *path, mode_t mode) {