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

2 files changed, 14 insertions, 0 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/BUILD b/pkg/sentry/fsimpl/kernfs/BUILD
index e73f1f857..b3d6299d0 100644
--- a/pkg/sentry/fsimpl/kernfs/BUILD
+++ b/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",
diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index 31da8b511..a429fa23d 100644
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/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()