Restore euid upon test finish

PiperOrigin-RevId: 307638329

1 files changed, 14 insertions, 5 deletions

diff --git a/test/syscalls/linux/uidgid.cc b/test/syscalls/linux/uidgid.cc
index ff66a79f4..64d6d0b8f 100644
--- a/test/syscalls/linux/uidgid.cc
+++ b/test/syscalls/linux/uidgid.cc
@@ -253,12 +253,21 @@ TEST(UidGidRootTest, Setgroups) {
 TEST(UidGidRootTest, Setuid_prlimit) {
   SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(IsRoot()));
 
-  // Change our UID.
-  EXPECT_THAT(seteuid(65534), SyscallSucceeds());
+  // Do seteuid in a separate thread so that after finishing this test, the
+  // process can still open files the test harness created before starting this
+  // test. Otherwise, the files are created by root (UID before the test), but
+  // cannot be opened by the `uid` set below after the test.
+  ScopedThread([&] {
+    // Use syscall instead of glibc setuid wrapper because we want this seteuid
+    // call to only apply to this task. POSIX threads, however, require that all
+    // threads have the same UIDs, so using the seteuid wrapper sets all
+    // threads' UID.
+    EXPECT_THAT(syscall(SYS_setreuid, -1, 65534), SyscallSucceeds());
 
-  // Despite the UID change, we should be able to get our own limits.
-  struct rlimit rl = {};
-  ASSERT_THAT(prlimit(0, RLIMIT_NOFILE, NULL, &rl), SyscallSucceeds());
+    // Despite the UID change, we should be able to get our own limits.
+    struct rlimit rl = {};
+    EXPECT_THAT(prlimit(0, RLIMIT_NOFILE, NULL, &rl), SyscallSucceeds());
+  });
 }
 
 }  // namespace