Add BoundEndpointAt filesystem operation.

BoundEndpointAt() is needed to support Unix sockets bound at a
file path, corresponding to BoundEndpoint() in VFS1.

Updates #1476.

PiperOrigin-RevId: 303258251

pkg/sentry/fsimpl/ext/BUILD

@@ -45,6 +45,7 @@ go_library(
         "//pkg/sentry/fsimpl/ext/disklayout",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/memmap",
+        "//pkg/sentry/socket/unix/transport",
         "//pkg/sentry/syscalls/linux",
         "//pkg/sentry/vfs",
         "//pkg/sync",

pkg/sentry/fsimpl/ext/filesystem.go

@@ -23,6 +23,7 @@ import (
 	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/ext/disklayout"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
@@ -463,6 +464,17 @@ func (fs *filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	return syserror.EROFS
 }
 
+// BoundEndpointAt implements FilesystemImpl.BoundEndpointAt.
+func (fs *filesystem) BoundEndpointAt(ctx context.Context, rp *vfs.ResolvingPath) (transport.BoundEndpoint, error) {
+	_, _, err := fs.walk(rp, false)
+	if err != nil {
+		return nil, err
+	}
+
+	// TODO(b/134676337): Support sockets.
+	return nil, syserror.ECONNREFUSED
+}
+
 // ListxattrAt implements vfs.FilesystemImpl.ListxattrAt.
 func (fs *filesystem) ListxattrAt(ctx context.Context, rp *vfs.ResolvingPath) ([]string, error) {
 	_, _, err := fs.walk(rp, false)

pkg/sentry/fsimpl/gofer/BUILD

@@ -46,6 +46,7 @@ go_library(
         "//pkg/sentry/memmap",
         "//pkg/sentry/pgalloc",
         "//pkg/sentry/platform",
+        "//pkg/sentry/socket/unix/transport",
         "//pkg/sentry/usage",
         "//pkg/sentry/vfs",
         "//pkg/syserror",

pkg/sentry/fsimpl/gofer/filesystem.go

@@ -22,6 +22,7 @@ import (
 	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/p9"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
@@ -1059,6 +1060,13 @@ func (fs *filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	return fs.unlinkAt(ctx, rp, false /* dir */)
 }
 
+// BoundEndpointAt implements FilesystemImpl.BoundEndpointAt.
+//
+// TODO(gvisor.dev/issue/1476): Implement BoundEndpointAt.
+func (fs *filesystem) BoundEndpointAt(ctx context.Context, rp *vfs.ResolvingPath) (transport.BoundEndpoint, error) {
+	return nil, syserror.ECONNREFUSED
+}
+
 // ListxattrAt implements vfs.FilesystemImpl.ListxattrAt.
 func (fs *filesystem) ListxattrAt(ctx context.Context, rp *vfs.ResolvingPath) ([]string, error) {
 	var ds *[]*dentry

pkg/sentry/fsimpl/kernfs/BUILD

@@ -35,6 +35,7 @@ go_library(
         "//pkg/refs",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/memmap",
+        "//pkg/sentry/socket/unix/transport",
         "//pkg/sentry/vfs",
         "//pkg/sync",
         "//pkg/syserror",

pkg/sentry/fsimpl/kernfs/filesystem.go

@@ -23,6 +23,7 @@ import (
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
@@ -728,6 +729,18 @@ func (fs *Filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	return nil
 }
 
+// BoundEndpointAt implements FilesystemImpl.BoundEndpointAt.
+func (fs *Filesystem) BoundEndpointAt(ctx context.Context, rp *vfs.ResolvingPath) (transport.BoundEndpoint, error) {
+	fs.mu.RLock()
+	_, _, err := fs.walkExistingLocked(ctx, rp)
+	fs.mu.RUnlock()
+	fs.processDeferredDecRefs()
+	if err != nil {
+		return nil, err
+	}
+	return nil, syserror.ECONNREFUSED
+}
+
 // ListxattrAt implements vfs.FilesystemImpl.ListxattrAt.
 func (fs *Filesystem) ListxattrAt(ctx context.Context, rp *vfs.ResolvingPath) ([]string, error) {
 	fs.mu.RLock()

pkg/sentry/fsimpl/tmpfs/BUILD

@@ -46,6 +46,7 @@ go_library(
         "//pkg/sentry/memmap",
         "//pkg/sentry/pgalloc",
         "//pkg/sentry/platform",
+        "//pkg/sentry/socket/unix/transport",
         "//pkg/sentry/usage",
         "//pkg/sentry/vfs",
         "//pkg/sentry/vfs/lock",

pkg/sentry/fsimpl/tmpfs/filesystem.go

@@ -21,6 +21,7 @@ import (
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
@@ -656,6 +657,13 @@ func (fs *filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	return nil
 }
 
+// BoundEndpointAt implements FilesystemImpl.BoundEndpointAt.
+//
+// TODO(gvisor.dev/issue/1476): Implement BoundEndpointAt.
+func (fs *filesystem) BoundEndpointAt(ctx context.Context, rp *vfs.ResolvingPath) (transport.BoundEndpoint, error) {
+	return nil, syserror.ECONNREFUSED
+}
+
 // ListxattrAt implements vfs.FilesystemImpl.ListxattrAt.
 func (fs *filesystem) ListxattrAt(ctx context.Context, rp *vfs.ResolvingPath) ([]string, error) {
 	fs.mu.RLock()

pkg/sentry/vfs/BUILD

@@ -53,6 +53,7 @@ go_library(
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/limits",
         "//pkg/sentry/memmap",
+        "//pkg/sentry/socket/unix/transport",
         "//pkg/sync",
         "//pkg/syserror",
         "//pkg/usermem",

pkg/sentry/vfs/anonfs.go

@@ -21,6 +21,7 @@ import (
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.dev/gvisor/pkg/syserror"
 	"gvisor.dev/gvisor/pkg/usermem"
 )
@@ -222,6 +223,14 @@ func (fs *anonFilesystem) UnlinkAt(ctx context.Context, rp *ResolvingPath) error
 	return syserror.EPERM
 }
 
+// BoundEndpointAt implements FilesystemImpl.BoundEndpointAt.
+func (fs *anonFilesystem) BoundEndpointAt(ctx context.Context, rp *ResolvingPath) (transport.BoundEndpoint, error) {
+	if !rp.Final() {
+		return nil, syserror.ENOTDIR
+	}
+	return nil, syserror.ECONNREFUSED
+}
+
 // ListxattrAt implements FilesystemImpl.ListxattrAt.
 func (fs *anonFilesystem) ListxattrAt(ctx context.Context, rp *ResolvingPath) ([]string, error) {
 	if !rp.Done() {

pkg/sentry/vfs/filesystem.go

@@ -21,6 +21,7 @@ import (
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 )
 
 // A Filesystem is a tree of nodes represented by Dentries, which forms part of
@@ -460,6 +461,11 @@ type FilesystemImpl interface {
 	// RemovexattrAt returns ENOTSUP.
 	RemovexattrAt(ctx context.Context, rp *ResolvingPath, name string) error
 
+	// BoundEndpointAt returns the Unix socket endpoint bound at the path rp.
+	//
+	// - If a non-socket file exists at rp, then BoundEndpointAt returns ECONNREFUSED.
+	BoundEndpointAt(ctx context.Context, rp *ResolvingPath) (transport.BoundEndpoint, error)
+
 	// PrependPath prepends a path from vd to vd.Mount().Root() to b.
 	//
 	// If vfsroot.Ok(), it is the contextual VFS root; if it is encountered
@@ -482,7 +488,7 @@ type FilesystemImpl interface {
 	// Preconditions: vd.Mount().Filesystem().Impl() == this FilesystemImpl.
 	PrependPath(ctx context.Context, vfsroot, vd VirtualDentry, b *fspath.Builder) error
 
-	// TODO: inotify_add_watch(); bind()
+	// TODO: inotify_add_watch()
 }
 
 // PrependPathAtVFSRootError is returned by implementations of

pkg/sentry/vfs/vfs.go

@@ -38,6 +38,7 @@ import (
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
+	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
@@ -230,7 +231,7 @@ func (vfs *VirtualFilesystem) getParentDirAndName(ctx context.Context, creds *au
 		}
 		if checkInvariants {
 			if rp.canHandleError(err) && rp.Done() {
-				panic(fmt.Sprintf("%T.GetParentDentryAt() consumed all path components and returned %T", rp.mount.fs.impl, err))
+				panic(fmt.Sprintf("%T.GetParentDentryAt() consumed all path components and returned %v", rp.mount.fs.impl, err))
 			}
 		}
 		if !rp.handleError(err) {
@@ -271,7 +272,7 @@ func (vfs *VirtualFilesystem) LinkAt(ctx context.Context, creds *auth.Credential
 		}
 		if checkInvariants {
 			if rp.canHandleError(err) && rp.Done() {
-				panic(fmt.Sprintf("%T.LinkAt() consumed all path components and returned %T", rp.mount.fs.impl, err))
+				panic(fmt.Sprintf("%T.LinkAt() consumed all path components and returned %v", rp.mount.fs.impl, err))
 			}
 		}
 		if !rp.handleError(err) {
@@ -307,7 +308,7 @@ func (vfs *VirtualFilesystem) MkdirAt(ctx context.Context, creds *auth.Credentia
 		}
 		if checkInvariants {
 			if rp.canHandleError(err) && rp.Done() {
-				panic(fmt.Sprintf("%T.MkdirAt() consumed all path components and returned %T", rp.mount.fs.impl, err))
+				panic(fmt.Sprintf("%T.MkdirAt() consumed all path components and returned %v", rp.mount.fs.impl, err))
 			}
 		}
 		if !rp.handleError(err) {
@@ -340,7 +341,7 @@ func (vfs *VirtualFilesystem) MknodAt(ctx context.Context, creds *auth.Credentia
 		}
 		if checkInvariants {
 			if rp.canHandleError(err) && rp.Done() {
-				panic(fmt.Sprintf("%T.MknodAt() consumed all path components and returned %T", rp.mount.fs.impl, err))
+				panic(fmt.Sprintf("%T.MknodAt() consumed all path components and returned %v", rp.mount.fs.impl, err))
 			}
 		}
 		if !rp.handleError(err) {
@@ -350,6 +351,33 @@ func (vfs *VirtualFilesystem) MknodAt(ctx context.Context, creds *auth.Credentia
 	}
 }
 
+// BoundEndpointAt gets the bound endpoint at the given path, if one exists.
+func (vfs *VirtualFilesystem) BoundEndpointAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation) (transport.BoundEndpoint, error) {
+	if !pop.Path.Begin.Ok() {
+		if pop.Path.Absolute {
+			return nil, syserror.ECONNREFUSED
+		}
+		return nil, syserror.ENOENT
+	}
+	rp := vfs.getResolvingPath(creds, pop)
+	for {
+		bep, err := rp.mount.fs.impl.BoundEndpointAt(ctx, rp)
+		if err == nil {
+			vfs.putResolvingPath(rp)
+			return bep, nil
+		}
+		if checkInvariants {
+			if rp.canHandleError(err) && rp.Done() {
+				panic(fmt.Sprintf("%T.BoundEndpointAt() consumed all path components and returned %v", rp.mount.fs.impl, err))
+			}
+		}
+		if !rp.handleError(err) {
+			vfs.putResolvingPath(rp)
+			return nil, err
+		}
+	}
+}
+
 // OpenAt returns a FileDescription providing access to the file at the given
 // path. A reference is taken on the returned FileDescription.
 func (vfs *VirtualFilesystem) OpenAt(ctx context.Context, creds *auth.Credentials, pop *PathOperation, opts *OpenOptions) (*FileDescription, error) {
@@ -494,7 +522,7 @@ func (vfs *VirtualFilesystem) RenameAt(ctx context.Context, creds *auth.Credenti
 		}
 		if checkInvariants {
 			if rp.canHandleError(err) && rp.Done() {
-				panic(fmt.Sprintf("%T.RenameAt() consumed all path components and returned %T", rp.mount.fs.impl, err))
+				panic(fmt.Sprintf("%T.RenameAt() consumed all path components and returned %v", rp.mount.fs.impl, err))
 			}
 		}
 		if !rp.handleError(err) {
@@ -527,7 +555,7 @@ func (vfs *VirtualFilesystem) RmdirAt(ctx context.Context, creds *auth.Credentia
 		}
 		if checkInvariants {
 			if rp.canHandleError(err) && rp.Done() {
-				panic(fmt.Sprintf("%T.RmdirAt() consumed all path components and returned %T", rp.mount.fs.impl, err))
+				panic(fmt.Sprintf("%T.RmdirAt() consumed all path components and returned %v", rp.mount.fs.impl, err))
 			}
 		}
 		if !rp.handleError(err) {
@@ -608,7 +636,7 @@ func (vfs *VirtualFilesystem) SymlinkAt(ctx context.Context, creds *auth.Credent
 		}
 		if checkInvariants {
 			if rp.canHandleError(err) && rp.Done() {
-				panic(fmt.Sprintf("%T.SymlinkAt() consumed all path components and returned %T", rp.mount.fs.impl, err))
+				panic(fmt.Sprintf("%T.SymlinkAt() consumed all path components and returned %v", rp.mount.fs.impl, err))
 			}
 		}
 		if !rp.handleError(err) {
@@ -640,7 +668,7 @@ func (vfs *VirtualFilesystem) UnlinkAt(ctx context.Context, creds *auth.Credenti
 		}
 		if checkInvariants {
 			if rp.canHandleError(err) && rp.Done() {
-				panic(fmt.Sprintf("%T.UnlinkAt() consumed all path components and returned %T", rp.mount.fs.impl, err))
+				panic(fmt.Sprintf("%T.UnlinkAt() consumed all path components and returned %v", rp.mount.fs.impl, err))
 			}
 		}
 		if !rp.handleError(err) {

pkg/syserror/syserror.go

@@ -27,6 +27,7 @@ import (
 var (
 	E2BIG        = error(syscall.E2BIG)
 	EACCES       = error(syscall.EACCES)
+	EADDRINUSE   = error(syscall.EADDRINUSE)
 	EAGAIN       = error(syscall.EAGAIN)
 	EBADF        = error(syscall.EBADF)
 	EBADFD       = error(syscall.EBADFD)