From 208f87f3873e3c4d8f644b66fbcca8c8b10fcf5b Mon Sep 17 00:00:00 2001
From: Ayush Ranjan <ayushranjan@google.com>
Date: Sun, 7 Aug 2022 00:05:53 -0700
Subject: [PATCH] Copy up consistently for all file types if open mode is
 writable.

Earlier, we were only copying up regular files. We were missing
out device files. ensureOpenableLocked() should ensure that
files are copied up if mode is writable. Without this, we
violate the preconditions for openCopiedUp().

Also, without this, open(file, O_WRONLY) on a lower layer pipe
returns EROFS, which is confusing because the upper layer is
still writable. Now it will return EPERM which indicates that
the pipe can not be copied up.

PiperOrigin-RevId: 465838606
---
 pkg/sentry/fsimpl/overlay/filesystem.go | 26 ++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/pkg/sentry/fsimpl/overlay/filesystem.go b/pkg/sentry/fsimpl/overlay/filesystem.go
index b53fa6b54..af97e324f 100644
--- a/pkg/sentry/fsimpl/overlay/filesystem.go
+++ b/pkg/sentry/fsimpl/overlay/filesystem.go
@@ -892,18 +892,7 @@ func (d *dentry) ensureOpenableLocked(ctx context.Context, rp *vfs.ResolvingPath
 	if err := d.checkPermissions(rp.Credentials(), ats); err != nil {
 		return err
 	}
-	switch d.mode.Load() & linux.S_IFMT {
-	case linux.S_IFREG:
-		if ats.MayWrite() {
-			if err := rp.Mount().CheckBeginWrite(); err != nil {
-				return err
-			}
-			defer rp.Mount().EndWrite()
-			if err := d.copyUpLocked(ctx); err != nil {
-				return err
-			}
-		}
-	case linux.S_IFDIR:
+	if d.isDir() {
 		if ats.MayWrite() {
 			return linuxerr.EISDIR
 		}
@@ -913,8 +902,19 @@ func (d *dentry) ensureOpenableLocked(ctx context.Context, rp *vfs.ResolvingPath
 		if opts.Flags&linux.O_DIRECT != 0 {
 			return linuxerr.EINVAL
 		}
+		return nil
 	}
-	return nil
+
+	if !ats.MayWrite() {
+		return nil
+	}
+
+	// Copy up!
+	if err := rp.Mount().CheckBeginWrite(); err != nil {
+		return err
+	}
+	defer rp.Mount().EndWrite()
+	return d.copyUpLocked(ctx)
 }
 
 // Preconditions: If vfs.AccessTypesForOpenFlags(opts).MayWrite(), then d has