Fix mknod and inotify syscall test

This change fixes a few things:
- creating sockets using mknod(2) is supported via vfs2
- fsgofer can create regular files via mknod(2)
- mode = 0 for mknod(2) will be interpreted as regular file in vfs2 as well

Updates #2923

PiperOrigin-RevId: 320074267

2 files changed, 10 insertions, 5 deletions

diff --git a/pkg/sentry/fsimpl/tmpfs/filesystem.go b/pkg/sentry/fsimpl/tmpfs/filesystem.go
index ed40f6b52..a0f20c2d4 100644
--- a/pkg/sentry/fsimpl/tmpfs/filesystem.go
+++ b/pkg/sentry/fsimpl/tmpfs/filesystem.go
@@ -277,7 +277,7 @@ func (fs *filesystem) MknodAt(ctx context.Context, rp *vfs.ResolvingPath, opts v
 		creds := rp.Credentials()
 		var childInode *inode
 		switch opts.Mode.FileType() {
-		case 0, linux.S_IFREG:
+		case linux.S_IFREG:
 			childInode = fs.newRegularFile(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode)
 		case linux.S_IFIFO:
 			childInode = fs.newNamedPipe(creds.EffectiveKUID, creds.EffectiveKGID, opts.Mode)
diff --git a/pkg/sentry/syscalls/linux/vfs2/filesystem.go b/pkg/sentry/syscalls/linux/vfs2/filesystem.go
index b12b5967b..6b14c2bef 100644
--- a/pkg/sentry/syscalls/linux/vfs2/filesystem.go
+++ b/pkg/sentry/syscalls/linux/vfs2/filesystem.go
@@ -107,7 +107,7 @@ func Mknod(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscall
 	addr := args[0].Pointer()
 	mode := args[1].ModeT()
 	dev := args[2].Uint()
-	return 0, nil, mknodat(t, linux.AT_FDCWD, addr, mode, dev)
+	return 0, nil, mknodat(t, linux.AT_FDCWD, addr, linux.FileMode(mode), dev)
 }
 
 // Mknodat implements Linux syscall mknodat(2).
@@ -116,10 +116,10 @@ func Mknodat(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sysca
 	addr := args[1].Pointer()
 	mode := args[2].ModeT()
 	dev := args[3].Uint()
-	return 0, nil, mknodat(t, dirfd, addr, mode, dev)
+	return 0, nil, mknodat(t, dirfd, addr, linux.FileMode(mode), dev)
 }
 
-func mknodat(t *kernel.Task, dirfd int32, addr usermem.Addr, mode uint, dev uint32) error {
+func mknodat(t *kernel.Task, dirfd int32, addr usermem.Addr, mode linux.FileMode, dev uint32) error {
 	path, err := copyInPath(t, addr)
 	if err != nil {
 		return err
@@ -129,9 +129,14 @@ func mknodat(t *kernel.Task, dirfd int32, addr usermem.Addr, mode uint, dev uint
 		return err
 	}
 	defer tpop.Release()
+
+	// "Zero file type is equivalent to type S_IFREG." - mknod(2)
+	if mode.FileType() == 0 {
+		mode |= linux.ModeRegular
+	}
 	major, minor := linux.DecodeDeviceID(dev)
 	return t.Kernel().VFS().MknodAt(t, t.Credentials(), &tpop.pop, &vfs.MknodOptions{
-		Mode:     linux.FileMode(mode &^ t.FSContext().Umask()),
+		Mode:     mode &^ linux.FileMode(t.FSContext().Umask()),
 		DevMajor: uint32(major),
 		DevMinor: minor,
 	})