[sanitizer] Add 'strip_env' flag to enable/disable removing sanitizer dylib from DYLD_INSERT_LIBRARIES

[kubamracek]

Summary

On macOS, we usually don't require launching the target with DYLD_INSERT_LIBRARIES anymore. However, it is still necessary when running a target that is not instrumented (and e.g. dlopen's an instrument library later). In any case, ASan and TSan currently remove themselves from the DYLD_INSERT_LIBRARIES environment variable to avoid passing it onto children. This works well e.g. when instrumenting a shell. A problem arises when the target is a non-instrumented shim (e.g. "xcrun") that either re-execs or launches a child that is supposed to get DYLD_INSERT_LIBRARIES propagated. To support this mode, this patch introduces 'strip_env' flag that can be used to keep DYLD_INSERT_LIBRARIES untouched.

[kubamracek]

ping

[fjricci]

Seems fine to me, and since nobody else has had any issue with it, I'll accept.

lib/sanitizer_common/sanitizer_flags.inc

COMMON_FLAG(
     "append executable name to logs (as in \"log_path.exe_name.pid\").")
 COMMON_FLAG(
     bool, log_to_syslog, SANITIZER_ANDROID || SANITIZER_MAC,
     "Write all sanitizer output to syslog in addition to other means of "
     "logging.")
 COMMON_FLAG(
     int, verbosity, 0,
     "Verbosity level (0 - silent, 1 - a bit of output, 2+ - more output).")
+COMMON_FLAG(bool, strip_env, 1,
+            "Whether to remove the sanitizer from DYLD_INSERT_LIBRARIES to "
+            "avoid passing it to children. Default is true.")
 COMMON_FLAG(bool, detect_leaks, !SANITIZER_MAC, "Enable memory leak detection.")
 COMMON_FLAG(
     bool, leak_check_at_exit, true,
     "Invoke leak checking in an atexit handler. Has no effect if "
     "detect_leaks=false, or if __lsan_do_leak_check() is called before the "
     "handler has a chance to run.")
 COMMON_FLAG(bool, allocator_may_return_null, false,
             "If false, the allocator will crash instead of returning 0 on "

lib/sanitizer_common/sanitizer_mac.cc

Report(
         "with:\n%s=%s\n",
         SanitizerToolName, kDyldInsertLibraries, info.dli_fname);
     RAW_CHECK("interceptors not installed" && 0);
   }
 
   if (!lib_is_in_env)
     return;
 
+  if (!common_flags()->strip_env)
+    return;
+
   // DYLD_INSERT_LIBRARIES is set and contains the runtime library. Let's remove
   // the dylib from the environment variable, because interceptors are installed
   // and we don't want our children to inherit the variable.
 
   uptr env_name_len = internal_strlen(kDyldInsertLibraries);
   // Allocate memory to hold the previous env var name, its value, the '='
   // sign and the '\0' char.
   char *new_env = (char*)allocator_for_env.Allocate(

test/asan/TestCases/Darwin/dyld_insert_libraries_remove.cc

 // RUN:   DYLD_INSERT_LIBRARIES=@executable_path/libclang_rt.asan_osx_dynamic.dylib:dummy-so.dylib \
 // RUN:   %run ./a.out 2>&1 ) | FileCheck %s || exit 1
 
 // RUN: ( cd %t && \
 // RUN:   DYLD_INSERT_LIBRARIES=libclang_rt.asan_osx_dynamic.dylib:dummy-so.dylib \
 // RUN:   %run ./a.out 2>&1 ) | FileCheck %s || exit 1
 
 // RUN: ( cd %t && \
+// RUN:   %env_asan_opts=strip_env=0 \
+// RUN:   DYLD_INSERT_LIBRARIES=libclang_rt.asan_osx_dynamic.dylib:dummy-so.dylib \
+// RUN:   %run ./a.out 2>&1 ) | FileCheck %s --check-prefix=CHECK-KEEP || exit 1
+
+// RUN: ( cd %t && \
 // RUN:   DYLD_INSERT_LIBRARIES=%t/libclang_rt.asan_osx_dynamic.dylib:dummy-so.dylib \
 // RUN:   %run ./a.out 2>&1 ) | FileCheck %s || exit 1
 
 #if !defined(SHARED_LIB)
 #include <stdio.h>
 #include <stdlib.h>
 
 int main() {
   const char kEnvName[] = "DYLD_INSERT_LIBRARIES";
   printf("%s=%s\n", kEnvName, getenv(kEnvName));
   // CHECK: {{DYLD_INSERT_LIBRARIES=dummy-so.dylib}}
+  // CHECK-KEEP: {{DYLD_INSERT_LIBRARIES=libclang_rt.asan_osx_dynamic.dylib:dummy-so.dylib}}
   return 0;
 }
 #else  // SHARED_LIB
 void foo() {}
 #endif  // SHARED_LIB