Handle AT_EMPTY_PATH flag in execveat.

PiperOrigin-RevId: 276419967

2 files changed, 24 insertions, 10 deletions

diff --git a/pkg/sentry/syscalls/linux/linux64_amd64.go b/pkg/sentry/syscalls/linux/linux64_amd64.go
index aedb6d774..6d3801ad9 100644
--- a/pkg/sentry/syscalls/linux/linux64_amd64.go
+++ b/pkg/sentry/syscalls/linux/linux64_amd64.go
@@ -362,7 +362,7 @@ var AMD64 = &kernel.SyscallTable{
 		319: syscalls.Supported("memfd_create", MemfdCreate),
 		320: syscalls.CapError("kexec_file_load", linux.CAP_SYS_BOOT, "", nil),
 		321: syscalls.CapError("bpf", linux.CAP_SYS_ADMIN, "", nil),
-		322: syscalls.PartiallySupported("execveat", Execveat, "No support for AT_EMPTY_PATH, AT_SYMLINK_FOLLOW.", nil),
+		322: syscalls.PartiallySupported("execveat", Execveat, "No support for AT_SYMLINK_FOLLOW.", nil),
 		323: syscalls.ErrorWithEvent("userfaultfd", syserror.ENOSYS, "", []string{"gvisor.dev/issue/266"}), // TODO(b/118906345)
 		324: syscalls.ErrorWithEvent("membarrier", syserror.ENOSYS, "", []string{"gvisor.dev/issue/267"}),  // TODO(b/118904897)
 		325: syscalls.PartiallySupported("mlock2", Mlock2, "Stub implementation. The sandbox lacks appropriate permissions.", nil),
diff --git a/pkg/sentry/syscalls/linux/sys_thread.go b/pkg/sentry/syscalls/linux/sys_thread.go
index 6e425f1ec..7ece7ba6f 100644
--- a/pkg/sentry/syscalls/linux/sys_thread.go
+++ b/pkg/sentry/syscalls/linux/sys_thread.go
@@ -105,18 +105,26 @@ func execveat(t *kernel.Task, dirFD int32, pathnameAddr, argvAddr, envvAddr user
 		}
 	}
 
-	if flags != 0 {
-		// TODO(b/128449944): Handle AT_EMPTY_PATH and AT_SYMLINK_NOFOLLOW.
+	if flags&linux.AT_SYMLINK_NOFOLLOW != 0 {
+		// TODO(b/128449944): Handle AT_SYMLINK_NOFOLLOW.
 		t.Kernel().EmitUnimplementedEvent(t)
 		return 0, nil, syserror.ENOSYS
 	}
 
+	atEmptyPath := flags&linux.AT_EMPTY_PATH != 0
+	if !atEmptyPath && len(pathname) == 0 {
+		return 0, nil, syserror.ENOENT
+	}
+
 	root := t.FSContext().RootDirectory()
 	defer root.DecRef()
 
 	var wd *fs.Dirent
+	var executable *fs.File
 	if dirFD == linux.AT_FDCWD || path.IsAbs(pathname) {
-		// If pathname is absolute, LoadTaskImage() will ignore the wd.
+		// Even if the pathname is absolute, we may still need the wd
+		// for interpreter scripts if the path of the interpreter is
+		// relative.
 		wd = t.FSContext().WorkingDirectory()
 	} else {
 		// Need to extract the given FD.
@@ -126,17 +134,23 @@ func execveat(t *kernel.Task, dirFD int32, pathnameAddr, argvAddr, envvAddr user
 		}
 		defer f.DecRef()
 
-		wd = f.Dirent
-		wd.IncRef()
-		if !fs.IsDir(wd.Inode.StableAttr) {
-			return 0, nil, syserror.ENOTDIR
+		if atEmptyPath && len(pathname) == 0 {
+			executable = f
+		} else {
+			wd = f.Dirent
+			wd.IncRef()
+			if !fs.IsDir(wd.Inode.StableAttr) {
+				return 0, nil, syserror.ENOTDIR
+			}
 		}
 	}
-	defer wd.DecRef()
+	if wd != nil {
+		defer wd.DecRef()
+	}
 
 	// Load the new TaskContext.
 	maxTraversals := uint(linux.MaxSymlinkTraversals)
-	tc, se := t.Kernel().LoadTaskImage(t, t.MountNamespace(), root, wd, &maxTraversals, pathname, nil, argv, envv, t.Arch().FeatureSet())
+	tc, se := t.Kernel().LoadTaskImage(t, t.MountNamespace(), root, wd, &maxTraversals, pathname, executable, argv, envv, t.Arch().FeatureSet())
 	if se != nil {
 		return 0, nil, se.ToError()
 	}