[sanitizer] Fix running sanitizer_bad_report_path_test on Linux as root

[iii-i]

Running tests as root is not the greatest idea, however, there is one
valid use case - running them in a container in order to verify LLVM on
different distros. There is no reason to configure unprivileged users
in a container, so one works as root.

sanitizer_bad_report_path_test assumes that creating a file in a
non-writable directory would fail, which is not the always case. For
example, when we are on Linux and CAP_DAC_OVERRIDE, which root has, is
in effect. Therefore, one solution is to drop it. However, that would
be Linux-specific.

Instead, use argv[0] as if it were a directory. mkdir() on top of a
file should be prohibited by all supported Posix operating systems.
Combine this with a partial revert of commit f4214e1469ad ("[sanitizer]
Skip test on Android where chmod is not working"), since we shouldn't
need to exclude Android anymore.

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Ilya Leoshkevich (iii-i)

Changes

Running tests as root is not the greatest idea, however, there is one valid use case - running them in a container in order to verify LLVM on different distros. There is no reason to configure unprivileged users in a container, so one works as root.

sanitizer_bad_report_path_test assumes that creating a file in a non-writable directory would fail, which is not the case if CAP_DAC_OVERRIDE, which root has, is in effect. So drop it.

---

Full diff: https://github.com/llvm/llvm-project/pull/97732.diff

1 Files Affected:

• (modified) compiler-rt/test/sanitizer_common/TestCases/Posix/sanitizer_bad_report_path_test.cpp (+23)

diff --git a/compiler-rt/test/sanitizer_common/TestCases/Posix/sanitizer_bad_report_path_test.cpp b/compiler-rt/test/sanitizer_common/TestCases/Posix/sanitizer_bad_report_path_test.cpp
index fd4abf448b09d..a7312341b6f5c 100644
--- a/compiler-rt/test/sanitizer_common/TestCases/Posix/sanitizer_bad_report_path_test.cpp
+++ b/compiler-rt/test/sanitizer_common/TestCases/Posix/sanitizer_bad_report_path_test.cpp
@@ -13,9 +13,32 @@
 #include <stdio.h>
 #include <string.h>
 
+#if defined(__linux__)
+#include <linux/capability.h>
+
+/* Use capget() and capset() from glibc. */
+extern "C" int capget(cap_user_header_t header, cap_user_data_t data);
+extern "C" int capset(cap_user_header_t header, const cap_user_data_t data);
+
+static void try_drop_cap_dac_override(void) {
+  struct __user_cap_header_struct hdr = {
+    .version = _LINUX_CAPABILITY_VERSION_1,
+    .pid = 0,
+  };
+  struct __user_cap_data_struct data[_LINUX_CAPABILITY_U32S_1];
+  if (!capget(&hdr, data)) {
+    data[CAP_DAC_OVERRIDE >> 5].effective &= ~(1 << (CAP_DAC_OVERRIDE & 31));
+    capset(&hdr, data);
+  }
+}
+#else
+static void try_drop_cap_dac_override(void) {}
+#endif
+
 volatile int *null = 0;
 
 int main(int argc, char **argv) {
+  try_drop_cap_dac_override();
   char buff[1000];
   sprintf(buff, "%s.report_path/report", argv[0]);
   __sanitizer_set_report_path(buff);

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[vitalybuka]

Nice

[iii-i]

Unfortunately this is now causing a buildbot failure on Android:

/var/lib/buildbot/sanitizer-buildbot6/sanitizer-x86_64-linux-android/build/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Posix/sanitizer_set_report_path_test.cpp:27:11: error: CHECK: expected string not found in input
// CHECK: ERROR: Can't create directory: {{.*}}Posix/Output/sanitizer_set_report_path_test.cpp.tmp
          ^
<stdin>:2:243: note: scanning from here
Path /data/local/tmp/Output/var/lib/buildbot/sanitizer-buildbot6/sanitizer-x86_64-linux-android/build/compiler_rt_build_android_arm/test/sanitizer_common/asan-arm-Android/Posix/Output/sanitizer_set_report_path_test.cpp.tmp.report_path/report.27545
                                                                                                                                                                                                                                                  ^

Input file: <stdin>
Check file: /var/lib/buildbot/sanitizer-buildbot6/sanitizer-x86_64-linux-android/build/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Posix/sanitizer_set_report_path_test.cpp

-dump-input=help explains the following input dump.

Input was:
<<<<<<
          1: ERROR: Can't create directory: /data/local/tmp/Output/var/lib/buildbot/sanitizer-buildbot6/sanitizer-x86_64-linux-android/build/compiler_rt_build_android_arm/test/sanitizer_common/asan-arm-Android/Posix/Output/sanitizer_set_report_path_test.cpp.tmp
          2: Path /data/local/tmp/Output/var/lib/buildbot/sanitizer-buildbot6/sanitizer-x86_64-linux-android/build/compiler_rt_build_android_arm/test/sanitizer_common/asan-arm-Android/Posix/Output/sanitizer_set_report_path_test.cpp.tmp.report_path/report.27545
check:27                                                                                                                                                                                                                                                       X~~~~~ error: no match found

The problem is that Path and ERROR: messages come in the wrong order. The first is fprintf()ed to stdout, the second is write()ten to stderr. The testcase merges the two file descriptors. But the interesting part is that the test calls fflush(stdout); in between.

I'm not sure how to investigate that fflush() ends up being a no-op on that builder. I propose to work around that by doing a write(kStderrFd) for the Path message. I will send a PR.

[iii-i]

I've posted #99469.