tmpfs: Allow xattrs in the trusted namespace if creds has CAP_SYS_ADMIN.

This is needed to support the overlay opaque attribute.

PiperOrigin-RevId: 328552985

4 files changed, 101 insertions, 16 deletions

diff --git a/test/syscalls/linux/memfd.cc b/test/syscalls/linux/memfd.cc
index f8b7f7938..4a450742b 100644
--- a/test/syscalls/linux/memfd.cc
+++ b/test/syscalls/linux/memfd.cc
@@ -14,12 +14,10 @@
 
 #include <errno.h>
 #include <fcntl.h>
-#include <linux/magic.h>
 #include <linux/memfd.h>
 #include <linux/unistd.h>
 #include <string.h>
 #include <sys/mman.h>
-#include <sys/statfs.h>
 #include <sys/syscall.h>
 
 #include <vector>
@@ -53,6 +51,7 @@ namespace {
 #define F_SEAL_GROW 0x0004
 #define F_SEAL_WRITE 0x0008
 
+using ::gvisor::testing::IsTmpfs;
 using ::testing::StartsWith;
 
 const std::string kMemfdName = "some-memfd";
@@ -444,20 +443,6 @@ TEST(MemfdTest, SealsAreInodeLevelProperties) {
   EXPECT_THAT(ftruncate(memfd3.get(), kPageSize), SyscallFailsWithErrno(EPERM));
 }
 
-PosixErrorOr<bool> IsTmpfs(const std::string& path) {
-  struct statfs stat;
-  if (statfs(path.c_str(), &stat)) {
-    if (errno == ENOENT) {
-      // Nothing at path, don't raise this as an error. Instead, just report no
-      // tmpfs at path.
-      return false;
-    }
-    return PosixError(errno,
-                      absl::StrFormat("statfs(\"%s\", %#p)", path, &stat));
-  }
-  return stat.f_type == TMPFS_MAGIC;
-}
-
 // Tmpfs files also support seals, but are created with F_SEAL_SEAL.
 TEST(MemfdTest, TmpfsFilesHaveSealSeal) {
   SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(IsTmpfs("/tmp")));
diff --git a/test/syscalls/linux/xattr.cc b/test/syscalls/linux/xattr.cc
index cbcf08451..5510a87a0 100644
--- a/test/syscalls/linux/xattr.cc
+++ b/test/syscalls/linux/xattr.cc
@@ -28,6 +28,7 @@
 #include "test/syscalls/linux/file_base.h"
 #include "test/util/capability_util.h"
 #include "test/util/file_descriptor.h"
+#include "test/util/fs_util.h"
 #include "test/util/posix_error.h"
 #include "test/util/temp_path.h"
 #include "test/util/test_util.h"
@@ -37,6 +38,8 @@ namespace testing {
 
 namespace {
 
+using ::gvisor::testing::IsTmpfs;
+
 class XattrTest : public FileTest {};
 
 TEST_F(XattrTest, XattrNonexistentFile) {
@@ -604,6 +607,77 @@ TEST_F(XattrTest, XattrWithFD) {
   EXPECT_THAT(fremovexattr(fd.get(), name), SyscallSucceeds());
 }
 
+TEST_F(XattrTest, TrustedNamespaceWithCapSysAdmin) {
+  // Trusted namespace not supported in VFS1.
+  SKIP_IF(IsRunningWithVFS1());
+
+  // TODO(b/66162845): Only gVisor tmpfs currently supports trusted namespace.
+  SKIP_IF(IsRunningOnGvisor() &&
+          !ASSERT_NO_ERRNO_AND_VALUE(IsTmpfs(test_file_name_)));
+
+  // Setting/Getting in the trusted namespace requires CAP_SYS_ADMIN.
+  SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN)));
+
+  const char* path = test_file_name_.c_str();
+  const char name[] = "trusted.test";
+
+  // Set.
+  char val = 'a';
+  size_t size = sizeof(val);
+  EXPECT_THAT(setxattr(path, name, &val, size, /*flags=*/0), SyscallSucceeds());
+
+  // Get.
+  char got = '\0';
+  EXPECT_THAT(getxattr(path, name, &got, size), SyscallSucceedsWithValue(size));
+  EXPECT_EQ(val, got);
+
+  // List.
+  char list[sizeof(name)];
+  EXPECT_THAT(listxattr(path, list, sizeof(list)),
+              SyscallSucceedsWithValue(sizeof(name)));
+  EXPECT_STREQ(list, name);
+
+  // Remove.
+  EXPECT_THAT(removexattr(path, name), SyscallSucceeds());
+
+  // Get should now return ENODATA.
+  EXPECT_THAT(getxattr(path, name, &got, size), SyscallFailsWithErrno(ENODATA));
+}
+
+TEST_F(XattrTest, TrustedNamespaceWithoutCapSysAdmin) {
+  // Trusted namespace not supported in VFS1.
+  SKIP_IF(IsRunningWithVFS1());
+
+  // TODO(b/66162845): Only gVisor tmpfs currently supports trusted namespace.
+  SKIP_IF(IsRunningOnGvisor() &&
+          !ASSERT_NO_ERRNO_AND_VALUE(IsTmpfs(test_file_name_)));
+
+  // Drop CAP_SYS_ADMIN if we have it.
+  if (ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN))) {
+    EXPECT_NO_ERRNO(SetCapability(CAP_SYS_ADMIN, false));
+  }
+
+  const char* path = test_file_name_.c_str();
+  const char name[] = "trusted.test";
+
+  // Set fails.
+  char val = 'a';
+  size_t size = sizeof(val);
+  EXPECT_THAT(setxattr(path, name, &val, size, /*flags=*/0),
+              SyscallFailsWithErrno(EPERM));
+
+  // Get fails.
+  char got = '\0';
+  EXPECT_THAT(getxattr(path, name, &got, size), SyscallFailsWithErrno(ENODATA));
+
+  // List still works, but returns no items.
+  char list[sizeof(name)];
+  EXPECT_THAT(listxattr(path, list, sizeof(list)), SyscallSucceedsWithValue(0));
+
+  // Remove fails.
+  EXPECT_THAT(removexattr(path, name), SyscallFailsWithErrno(EPERM));
+}
+
 }  // namespace
 
 }  // namespace testing
diff --git a/test/util/fs_util.cc b/test/util/fs_util.cc
index 5418948fe..dffa16183 100644
--- a/test/util/fs_util.cc
+++ b/test/util/fs_util.cc
@@ -15,7 +15,11 @@
 #include "test/util/fs_util.h"
 
 #include <dirent.h>
+#ifndef __fuchsia__
+#include <linux/magic.h>
+#endif  // __fuchsia__
 #include <sys/stat.h>
+#include <sys/statfs.h>
 #include <sys/types.h>
 #include <unistd.h>
 
@@ -629,5 +633,21 @@ PosixErrorOr<std::string> ProcessExePath(int pid) {
   return ReadLink(absl::StrCat("/proc/", pid, "/exe"));
 }
 
+#ifndef __fuchsia__
+PosixErrorOr<bool> IsTmpfs(const std::string& path) {
+  struct statfs stat;
+  if (statfs(path.c_str(), &stat)) {
+    if (errno == ENOENT) {
+      // Nothing at path, don't raise this as an error. Instead, just report no
+      // tmpfs at path.
+      return false;
+    }
+    return PosixError(errno,
+                      absl::StrFormat("statfs(\"%s\", %#p)", path, &stat));
+  }
+  return stat.f_type == TMPFS_MAGIC;
+}
+#endif  // __fuchsia__
+
 }  // namespace testing
 }  // namespace gvisor
diff --git a/test/util/fs_util.h b/test/util/fs_util.h
index 8cdac23a1..044190657 100644
--- a/test/util/fs_util.h
+++ b/test/util/fs_util.h
@@ -17,6 +17,7 @@
 
 #include <dirent.h>
 #include <sys/stat.h>
+#include <sys/statfs.h>
 #include <sys/types.h>
 #include <unistd.h>
 
@@ -178,6 +179,11 @@ std::string CleanPath(absl::string_view path);
 // Returns the full path to the executable of the given pid or a PosixError.
 PosixErrorOr<std::string> ProcessExePath(int pid);
 
+#ifndef __fuchsia__
+// IsTmpfs returns true if the file at path is backed by tmpfs.
+PosixErrorOr<bool> IsTmpfs(const std::string& path);
+#endif  // __fucshia__
+
 namespace internal {
 // Not part of the public API.
 std::string JoinPathImpl(std::initializer_list<absl::string_view> paths);