Remove side effect from mount tests

Dropping CAP_SYS_ADMIN and not restoring it causes
other tests to be skipped.

PiperOrigin-RevId: 370002644

3 files changed, 19 insertions, 5 deletions

diff --git a/test/syscalls/linux/mount.cc b/test/syscalls/linux/mount.cc
index cdc223d07..92d0fb05c 100644
--- a/test/syscalls/linux/mount.cc
+++ b/test/syscalls/linux/mount.cc
@@ -67,9 +67,7 @@ TEST(MountTest, MountInvalidTarget) {
 
 TEST(MountTest, MountPermDenied) {
   // Clear CAP_SYS_ADMIN.
-  if (ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN))) {
-    EXPECT_NO_ERRNO(SetCapability(CAP_SYS_ADMIN, false));
-  }
+  AutoCapability cap(CAP_SYS_ADMIN, false);
 
   // Linux expects a valid target before checking capability.
   auto const dir = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
diff --git a/test/util/capability_util.h b/test/util/capability_util.h
index a03bc7e05..f2c370125 100644
--- a/test/util/capability_util.h
+++ b/test/util/capability_util.h
@@ -99,14 +99,23 @@ PosixErrorOr<bool> CanCreateUserNamespace();
 class AutoCapability {
  public:
   AutoCapability(int cap, bool set) : cap_(cap), set_(set) {
-    EXPECT_NO_ERRNO(SetCapability(cap_, set_));
+    const bool has = EXPECT_NO_ERRNO_AND_VALUE(HaveCapability(cap));
+    if (set != has) {
+      EXPECT_NO_ERRNO(SetCapability(cap_, set_));
+      applied_ = true;
+    }
   }
 
-  ~AutoCapability() { EXPECT_NO_ERRNO(SetCapability(cap_, !set_)); }
+  ~AutoCapability() {
+    if (applied_) {
+      EXPECT_NO_ERRNO(SetCapability(cap_, !set_));
+    }
+  }
 
  private:
   int cap_;
   bool set_;
+  bool applied_ = false;
 };
 
 }  // namespace testing
diff --git a/test/util/posix_error.h b/test/util/posix_error.h
index 27557ad44..9ca09b77c 100644
--- a/test/util/posix_error.h
+++ b/test/util/posix_error.h
@@ -438,6 +438,13 @@ IsPosixErrorOkAndHolds(InnerMatcher&& inner_matcher) {
     std::move(_expr_result).ValueOrDie(); \
   })
 
+#define EXPECT_NO_ERRNO_AND_VALUE(expr)   \
+  ({                                      \
+    auto _expr_result = (expr);           \
+    EXPECT_NO_ERRNO(_expr_result);        \
+    std::move(_expr_result).ValueOrDie(); \
+  })
+
 }  // namespace testing
 }  // namespace gvisor