Fix vfs2 handling of preadv2/pwritev2 flags.

Check for unsupported flags, and silently support RWF_HIPRI by doing nothing.
From pkg/abi/linux/file.go: "gVisor does not implement the RWF_HIPRI feature,
but the flag is accepted as a valid flag argument for preadv2/pwritev2."

Updates #2923.

PiperOrigin-RevId: 317330631

2 files changed, 13 insertions, 4 deletions

diff --git a/pkg/sentry/fsimpl/gofer/regular_file.go b/pkg/sentry/fsimpl/gofer/regular_file.go
index f7a15a2ed..404a452c4 100644
--- a/pkg/sentry/fsimpl/gofer/regular_file.go
+++ b/pkg/sentry/fsimpl/gofer/regular_file.go
@@ -72,7 +72,9 @@ func (fd *regularFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offs
 	if offset < 0 {
 		return 0, syserror.EINVAL
 	}
-	if opts.Flags != 0 {
+
+	// Check that flags are supported. Silently ignore RWF_HIPRI.
+	if opts.Flags&^linux.RWF_HIPRI != 0 {
 		return 0, syserror.EOPNOTSUPP
 	}
 
@@ -123,9 +125,12 @@ func (fd *regularFileFD) PWrite(ctx context.Context, src usermem.IOSequence, off
 	if offset < 0 {
 		return 0, syserror.EINVAL
 	}
-	if opts.Flags != 0 {
+
+	// Check that flags are supported. Silently ignore RWF_HIPRI.
+	if opts.Flags&^linux.RWF_HIPRI != 0 {
 		return 0, syserror.EOPNOTSUPP
 	}
+
 	limit, err := vfs.CheckLimit(ctx, offset, src.NumBytes())
 	if err != nil {
 		return 0, err
diff --git a/pkg/sentry/fsimpl/gofer/special_file.go b/pkg/sentry/fsimpl/gofer/special_file.go
index a92008208..a016cbae1 100644
--- a/pkg/sentry/fsimpl/gofer/special_file.go
+++ b/pkg/sentry/fsimpl/gofer/special_file.go
@@ -129,7 +129,9 @@ func (fd *specialFileFD) PRead(ctx context.Context, dst usermem.IOSequence, offs
 	if fd.seekable && offset < 0 {
 		return 0, syserror.EINVAL
 	}
-	if opts.Flags != 0 {
+
+	// Check that flags are supported. Silently ignore RWF_HIPRI.
+	if opts.Flags&^linux.RWF_HIPRI != 0 {
 		return 0, syserror.EOPNOTSUPP
 	}
 
@@ -173,7 +175,9 @@ func (fd *specialFileFD) PWrite(ctx context.Context, src usermem.IOSequence, off
 	if fd.seekable && offset < 0 {
 		return 0, syserror.EINVAL
 	}
-	if opts.Flags != 0 {
+
+	// Check that flags are supported. Silently ignore RWF_HIPRI.
+	if opts.Flags&^linux.RWF_HIPRI != 0 {
 		return 0, syserror.EOPNOTSUPP
 	}