From dbe4176565b56d9e2f5395e410468a4c98aafd37 Mon Sep 17 00:00:00 2001 From: Fabricio Voznika Date: Thu, 14 Jan 2021 13:41:25 -0800 Subject: Check for existence before permissions Return EEXIST when overwritting a file as long as the caller has exec permission on the parent directory, even if the caller doesn't have write permission. Also reordered the mount write check, which happens before permission is checked. Closes #5164 PiperOrigin-RevId: 351868123 --- pkg/sentry/fsimpl/tmpfs/filesystem.go | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'pkg/sentry/fsimpl/tmpfs/filesystem.go') diff --git a/pkg/sentry/fsimpl/tmpfs/filesystem.go b/pkg/sentry/fsimpl/tmpfs/filesystem.go index 9296db2fb..453e41d11 100644 --- a/pkg/sentry/fsimpl/tmpfs/filesystem.go +++ b/pkg/sentry/fsimpl/tmpfs/filesystem.go @@ -153,7 +153,10 @@ func (fs *filesystem) doCreateAt(ctx context.Context, rp *vfs.ResolvingPath, dir if err != nil { return err } - if err := parentDir.inode.checkPermissions(rp.Credentials(), vfs.MayWrite|vfs.MayExec); err != nil { + + // Order of checks is important. First check if parent directory can be + // executed, then check for existence, and lastly check if mount is writable. + if err := parentDir.inode.checkPermissions(rp.Credentials(), vfs.MayExec); err != nil { return err } name := rp.Component() @@ -179,6 +182,10 @@ func (fs *filesystem) doCreateAt(ctx context.Context, rp *vfs.ResolvingPath, dir return err } defer mnt.EndWrite() + + if err := parentDir.inode.checkPermissions(rp.Credentials(), vfs.MayWrite); err != nil { + return err + } if err := create(parentDir, name); err != nil { return err } -- cgit v1.2.3