From 2df63d7799b49beaca900e155b5b662f21ce453e Mon Sep 17 00:00:00 2001
From: Ayush Ranjan <ayushranjan@google.com>
Date: Thu, 26 Oct 2023 12:00:38 -0700
Subject: [PATCH] Ignore AT_NO_AUTOMOUNT flag in fstatat(2).

Similar to our approach in statx(2). Binaries like mount(1) are using this flag
and if we don't support it, we get confusing error messages.

PiperOrigin-RevId: 576946190
---
 pkg/sentry/syscalls/linux/sys_stat.go |  3 +++
 test/syscalls/linux/stat.cc           | 22 +++++++++++++---------
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/pkg/sentry/syscalls/linux/sys_stat.go b/pkg/sentry/syscalls/linux/sys_stat.go
index 4386debe6..1daf76b18 100644
--- a/pkg/sentry/syscalls/linux/sys_stat.go
+++ b/pkg/sentry/syscalls/linux/sys_stat.go
@@ -50,6 +50,9 @@ func Newfstatat(t *kernel.Task, sysno uintptr, args arch.SyscallArguments) (uint
 }
 
 func fstatat(t *kernel.Task, dirfd int32, pathAddr, statAddr hostarch.Addr, flags int32) error {
+	// TODO(b/270247637): gVisor does not yet support automount, so
+	// AT_NO_AUTOMOUNT flag is a no-op.
+	flags &= ^linux.AT_NO_AUTOMOUNT
 	if flags&^(linux.AT_EMPTY_PATH|linux.AT_SYMLINK_NOFOLLOW) != 0 {
 		return linuxerr.EINVAL
 	}
diff --git a/test/syscalls/linux/stat.cc b/test/syscalls/linux/stat.cc
index 2ac2218df..8c3a9042d 100644
--- a/test/syscalls/linux/stat.cc
+++ b/test/syscalls/linux/stat.cc
@@ -783,16 +783,20 @@ TEST_F(StatTest, StatxInvalidFlags) {
               SyscallFailsWithErrno(EINVAL));
 }
 
-TEST_F(StatTest, StatxIgnoreNoAutomount) {
-  SKIP_IF(!IsRunningOnGvisor() && statx(-1, nullptr, 0, 0, nullptr) < 0 &&
-          errno == ENOSYS);
+// TODO(b/270247637): AT_NO_AUTOMOUNT flag has no effect because gVisor does
+// not support automount yet.
+TEST_F(StatTest, StatIgnoreNoAutomount) {
+  if (IsRunningOnGvisor() || statx(-1, nullptr, 0, 0, nullptr) == 0 ||
+      errno != ENOSYS) {
+    struct kernel_statx stx;
+    EXPECT_THAT(
+        statx(-1, test_file_name_.c_str(), AT_NO_AUTOMOUNT, STATX_ALL, &stx),
+        SyscallSucceeds());
+  }
 
-  // NOTE(b/270219255): AT_NO_AUTOMOUNT flag has no effect because gVisor does
-  // not support automount.
-  struct kernel_statx stx;
-  EXPECT_THAT(
-      statx(-1, test_file_name_.c_str(), AT_NO_AUTOMOUNT, STATX_ALL, &stx),
-      SyscallSucceeds());
+  struct stat st;
+  EXPECT_THAT(fstatat(AT_FDCWD, test_file_name_.c_str(), &st, AT_NO_AUTOMOUNT),
+              SyscallSucceeds());
 }
 
 }  // namespace