Add support for STATX_MNT_ID in statx.

PiperOrigin-RevId: 889466880

Author: manninglucas

pkg/abi/linux/file.go

@@ -266,6 +266,7 @@ const (
 	STATX_BLOCKS      = 0x00000400
 	STATX_BASIC_STATS = 0x000007ff
 	STATX_BTIME       = 0x00000800
+	STATX_MNT_ID      = 0x00001000
 	STATX_ALL         = 0x00000fff
 	STATX__RESERVED   = 0x80000000
 )
@@ -306,12 +307,13 @@ type Statx struct {
 	RdevMinor      uint32
 	DevMajor       uint32
 	DevMinor       uint32
+	MntID          uint64
 }
 
 // String implements fmt.Stringer.String.
 func (s *Statx) String() string {
-	return fmt.Sprintf("Statx{Mask: %#x, Mode: %s, UID: %d, GID: %d, Ino: %d, DevMajor: %d, DevMinor: %d, Size: %d, Blocks: %d, Blksize: %d, Nlink: %d, Atime: %s, Btime: %s, Ctime: %s, Mtime: %s, Attributes: %d, AttributesMask: %d, RdevMajor: %d, RdevMinor: %d}",
-		s.Mask, FileMode(s.Mode), s.UID, s.GID, s.Ino, s.DevMajor, s.DevMinor, s.Size, s.Blocks, s.Blksize, s.Nlink, s.Atime.ToTime(), s.Btime.ToTime(), s.Ctime.ToTime(), s.Mtime.ToTime(), s.Attributes, s.AttributesMask, s.RdevMajor, s.RdevMinor)
+	return fmt.Sprintf("Statx{Mask: %#x, Mode: %s, UID: %d, GID: %d, Ino: %d, DevMajor: %d, DevMinor: %d, Size: %d, Blocks: %d, Blksize: %d, Nlink: %d, Atime: %s, Btime: %s, Ctime: %s, Mtime: %s, Attributes: %d, AttributesMask: %d, RdevMajor: %d, RdevMinor: %d, MntId: %d}",
+		s.Mask, FileMode(s.Mode), s.UID, s.GID, s.Ino, s.DevMajor, s.DevMinor, s.Size, s.Blocks, s.Blksize, s.Nlink, s.Atime.ToTime(), s.Btime.ToTime(), s.Ctime.ToTime(), s.Mtime.ToTime(), s.Attributes, s.AttributesMask, s.RdevMajor, s.RdevMinor, s.MntID)
 }
 
 // SizeOfStatx is the size of a Statx struct.

pkg/sentry/vfs/file_description.go

@@ -540,17 +540,26 @@ func (fd *FileDescription) OnClose(ctx context.Context) error {
 
 // Stat returns metadata for the file represented by fd.
 func (fd *FileDescription) Stat(ctx context.Context, opts StatOptions) (linux.Statx, error) {
+	var (
+		stat linux.Statx
+		err  error
+	)
 	if fd.opts.UseDentryMetadata {
 		vfsObj := fd.vd.mount.vfs
 		rp := vfsObj.getResolvingPath(auth.CredentialsFromContext(ctx), &PathOperation{
 			Root:  fd.vd,
 			Start: fd.vd,
 		})
-		stat, err := fd.vd.mount.fs.impl.StatAt(ctx, rp, opts)
+		stat, err = fd.vd.mount.fs.impl.StatAt(ctx, rp, opts)
 		rp.Release(ctx)
-		return stat, err
+	} else {
+		stat, err = fd.impl.Stat(ctx, opts)
 	}
-	return fd.impl.Stat(ctx, opts)
+	if err == nil && opts.Mask&linux.STATX_MNT_ID != 0 {
+		stat.MntID = fd.vd.mount.ID
+		stat.Mask |= linux.STATX_MNT_ID
+	}
+	return stat, err
 }
 
 // SetStat updates metadata for the file represented by fd.

pkg/sentry/vfs/vfs.go

@@ -640,6 +640,10 @@ func (vfs *VirtualFilesystem) StatAt(ctx context.Context, creds *auth.Credential
 		}
 		stat, err := rp.mount.fs.impl.StatAt(ctx, rp, *opts)
 		if err == nil {
+			if opts.Mask&linux.STATX_MNT_ID != 0 {
+				stat.MntID = rp.mount.ID
+				stat.Mask |= linux.STATX_MNT_ID
+			}
 			return stat, nil
 		}
 		if !rp.handleError(ctx, err) {

test/syscalls/linux/BUILD

@@ -4084,6 +4084,7 @@ cc_binary(
     linkstatic = 1,
     malloc = "//test/util:errno_safe_allocator",
     deps = select_gtest() + [
+        "//test/util:capability_util",
         "//test/util:cleanup",
         "//test/util:file_descriptor",
         "//test/util:fs_util",

test/syscalls/linux/stat.cc

@@ -14,6 +14,8 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <linux/capability.h>
+#include <sys/mount.h>
 #include <sys/stat.h>
 #include <sys/statfs.h>
 #include <sys/types.h>
@@ -31,6 +33,8 @@
 #include "test/util/cleanup.h"
 #include "test/util/file_descriptor.h"
 #include "test/util/fs_util.h"
+#include "test/util/linux_capability_util.h"
+#include "test/util/posix_error.h"
 #include "test/util/save_util.h"
 #include "test/util/temp_path.h"
 #include "test/util/test_util.h"
@@ -680,6 +684,10 @@ TEST(SimpleStatTest, AnonDeviceAllocatesUniqueInodesAcrossSaveRestore) {
 #define STATX_ALL 0x00000fffU
 #endif  // STATX_ALL
 
+#ifndef STATX_MNT_ID
+#define STATX_MNT_ID 0x00001000U
+#endif  // STATX_MNT_ID
+
 // struct kernel_statx_timestamp is a Linux statx_timestamp struct.
 struct kernel_statx_timestamp {
   int64_t tv_sec;
@@ -710,6 +718,7 @@ struct kernel_statx {
   uint32_t stx_rdev_minor;
   uint32_t stx_dev_major;
   uint32_t stx_dev_minor;
+  uint64_t stx_mnt_id;
   uint64_t __spare2[14];
 };
 
@@ -835,6 +844,53 @@ TEST_F(StatTest, StatIgnoreNoAutomount) {
               SyscallSucceeds());
 }
 
+TEST_F(StatTest, StatxMntId) {
+  SKIP_IF(!IsRunningOnGvisor() && statx(-1, nullptr, 0, 0, nullptr) < 0 &&
+          errno == ENOSYS);
+
+  struct kernel_statx stx;
+  EXPECT_THAT(statx(AT_FDCWD, test_file_name_.c_str(), 0, STATX_MNT_ID, &stx),
+              SyscallSucceeds());
+  EXPECT_TRUE(stx.stx_mask & STATX_MNT_ID);
+  EXPECT_NE(stx.stx_mnt_id, 0);
+
+  // Check that two files in the same mount have the same mount ID.
+  TempPath file2 = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  struct kernel_statx stx2;
+  EXPECT_THAT(statx(AT_FDCWD, file2.path().c_str(), 0, STATX_MNT_ID, &stx2),
+              SyscallSucceeds());
+  EXPECT_TRUE(stx2.stx_mask & STATX_MNT_ID);
+  EXPECT_EQ(stx.stx_mnt_id, stx2.stx_mnt_id);
+}
+
+TEST_F(StatTest, StatxMntIdBindMount) {
+  SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN)));
+  SKIP_IF(!IsRunningOnGvisor() && statx(-1, nullptr, 0, 0, nullptr) < 0 &&
+          errno == ENOSYS);
+
+  TempPath dir1 = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+  TempPath dir2 = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDir());
+
+  struct kernel_statx stx1;
+  EXPECT_THAT(statx(AT_FDCWD, dir1.path().c_str(), 0, STATX_MNT_ID, &stx1),
+              SyscallSucceeds());
+
+  ASSERT_THAT(mount(dir1.path().c_str(), dir2.path().c_str(), nullptr, MS_BIND,
+                    nullptr),
+              SyscallSucceeds());
+  auto cleanup = Cleanup([&dir2]() {
+    ASSERT_THAT(umount(dir2.path().c_str()), SyscallSucceeds());
+  });
+
+  struct kernel_statx stx2;
+  EXPECT_THAT(statx(AT_FDCWD, dir2.path().c_str(), 0, STATX_MNT_ID, &stx2),
+              SyscallSucceeds());
+
+  EXPECT_TRUE(stx1.stx_mask & STATX_MNT_ID);
+  EXPECT_TRUE(stx2.stx_mask & STATX_MNT_ID);
+  EXPECT_NE(stx1.stx_mnt_id, stx2.stx_mnt_id);
+}
+
 }  // namespace
 
 }  // namespace testing