Add missing error checks for FileDescription.Init.

Syzkaller discovered this bug in pipefs by doing something quite strange:
creat(&(0x7f0000002a00)='./file1\x00', 0x0)
mount(&(0x7f0000000440)=ANY=[], &(0x7f00000002c0)='./file1\x00', &(0x7f0000000300)='devtmpfs\x00', 0x20000d, 0x0)
creat(&(0x7f0000000000)='./file1/file0\x00', 0x0)

This can be reproduced with:
touch mymount
mkfifo /dev/mypipe
mount -o ro -t devtmpfs devtmpfs mymount
echo 123 > mymount/mypipe

PiperOrigin-RevId: 349687714

pkg/sentry/fsimpl/ext/inode.go

@@ -200,7 +200,9 @@ func (in *inode) open(rp *vfs.ResolvingPath, vfsd *vfs.Dentry, opts *vfs.OpenOpt
 		}
 		var fd symlinkFD
 		fd.LockFD.Init(&in.locks)
-		fd.vfsfd.Init(&fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{})
+		if err := fd.vfsfd.Init(&fd, opts.Flags, mnt, vfsd, &vfs.FileDescriptionOptions{}); err != nil {
+			return nil, err
+		}
 		return &fd.vfsfd, nil
 	default:
 		panic(fmt.Sprintf("unknown inode type: %T", in.impl))

pkg/sentry/fsimpl/pipefs/pipefs.go

@@ -164,11 +164,11 @@ func (i *inode) StatFS(ctx context.Context, fs *vfs.Filesystem) (linux.Statfs, e
 // and write ends of a newly-created pipe, as for pipe(2) and pipe2(2).
 //
 // Preconditions: mnt.Filesystem() must have been returned by NewFilesystem().
-func NewConnectedPipeFDs(ctx context.Context, mnt *vfs.Mount, flags uint32) (*vfs.FileDescription, *vfs.FileDescription) {
+func NewConnectedPipeFDs(ctx context.Context, mnt *vfs.Mount, flags uint32) (*vfs.FileDescription, *vfs.FileDescription, error) {
 	fs := mnt.Filesystem().Impl().(*filesystem)
 	inode := newInode(ctx, fs)
 	var d kernfs.Dentry
 	d.Init(&fs.Filesystem, inode)
 	defer d.DecRef(ctx)
-	return inode.pipe.ReaderWriterPair(mnt, d.VFSDentry(), flags)
+	return inode.pipe.ReaderWriterPair(ctx, mnt, d.VFSDentry(), flags)
 }

pkg/sentry/kernel/pipe/vfs.go

@@ -63,10 +63,19 @@ func NewVFSPipe(isNamed bool, sizeBytes int64) *VFSPipe {
 // ReaderWriterPair returns read-only and write-only FDs for vp.
 //
 // Preconditions: statusFlags should not contain an open access mode.
-func (vp *VFSPipe) ReaderWriterPair(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32) (*vfs.FileDescription, *vfs.FileDescription) {
+func (vp *VFSPipe) ReaderWriterPair(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32) (*vfs.FileDescription, *vfs.FileDescription, error) {
 	// Connected pipes share the same locks.
 	locks := &vfs.FileLocks{}
-	return vp.newFD(mnt, vfsd, linux.O_RDONLY|statusFlags, locks), vp.newFD(mnt, vfsd, linux.O_WRONLY|statusFlags, locks)
+	r, err := vp.newFD(mnt, vfsd, linux.O_RDONLY|statusFlags, locks)
+	if err != nil {
+		return nil, nil, err
+	}
+	w, err := vp.newFD(mnt, vfsd, linux.O_WRONLY|statusFlags, locks)
+	if err != nil {
+		r.DecRef(ctx)
+		return nil, nil, err
+	}
+	return r, w, nil
 }
 
 // Allocate implements vfs.FileDescriptionImpl.Allocate.
@@ -85,7 +94,10 @@ func (vp *VFSPipe) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, s
 		return nil, syserror.EINVAL
 	}
 
-	fd := vp.newFD(mnt, vfsd, statusFlags, locks)
+	fd, err := vp.newFD(mnt, vfsd, statusFlags, locks)
+	if err != nil {
+		return nil, err
+	}
 
 	// Named pipes have special blocking semantics during open:
 	//
@@ -137,16 +149,18 @@ func (vp *VFSPipe) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, s
 }
 
 // Preconditions: vp.mu must be held.
-func (vp *VFSPipe) newFD(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32, locks *vfs.FileLocks) *vfs.FileDescription {
+func (vp *VFSPipe) newFD(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32, locks *vfs.FileLocks) (*vfs.FileDescription, error) {
 	fd := &VFSPipeFD{
 		pipe: &vp.pipe,
 	}
 	fd.LockFD.Init(locks)
-	fd.vfsfd.Init(fd, statusFlags, mnt, vfsd, &vfs.FileDescriptionOptions{
+	if err := fd.vfsfd.Init(fd, statusFlags, mnt, vfsd, &vfs.FileDescriptionOptions{
 		DenyPRead:         true,
 		DenyPWrite:        true,
 		UseDentryMetadata: true,
-	})
+	}); err != nil {
+		return nil, err
+	}
 
 	switch {
 	case fd.vfsfd.IsReadable() && fd.vfsfd.IsWritable():
@@ -160,7 +174,7 @@ func (vp *VFSPipe) newFD(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32, l
 		panic("invalid pipe flags: must be readable, writable, or both")
 	}
 
-	return &fd.vfsfd
+	return &fd.vfsfd, nil
 }
 
 // VFSPipeFD implements vfs.FileDescriptionImpl for pipes. It also implements

pkg/sentry/syscalls/linux/vfs2/pipe.go

@@ -42,7 +42,10 @@ func pipe2(t *kernel.Task, addr usermem.Addr, flags int32) error {
 	if flags&^(linux.O_NONBLOCK|linux.O_CLOEXEC) != 0 {
 		return syserror.EINVAL
 	}
-	r, w := pipefs.NewConnectedPipeFDs(t, t.Kernel().PipeMount(), uint32(flags&linux.O_NONBLOCK))
+	r, w, err := pipefs.NewConnectedPipeFDs(t, t.Kernel().PipeMount(), uint32(flags&linux.O_NONBLOCK))
+	if err != nil {
+		return err
+	}
 	defer r.DecRef(t)
 	defer w.DecRef(t)