Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753274AbeAFKFq (ORCPT + 1 other); Sat, 6 Jan 2018 05:05:46 -0500 Received: from mail-lf0-f66.google.com ([209.85.215.66]:33987 "EHLO mail-lf0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752863AbeAFKFn (ORCPT ); Sat, 6 Jan 2018 05:05:43 -0500 X-Google-Smtp-Source: ACJfBoserItGLqI5pQnNKWyF9yrsD3OXnnIIzN5FImkL5zhfoXCZTzqS8ZPLyExjptO1dbbn+ND8kg== Subject: Re: [PATCH 15/18] vfs, fdtable: prevent bounds-check bypass via speculative execution To: Dan Williams , linux-kernel@vger.kernel.org Cc: linux-arch@vger.kernel.org, peterz@infradead.org, netdev@vger.kernel.org, Al Viro , gregkh@linuxfoundation.org, tglx@linutronix.de, torvalds@linux-foundation.org, Elena Reshetova , alan@linux.intel.com References: <151520099201.32271.4677179499894422956.stgit@dwillia2-desk3.amr.corp.intel.com> <151520107515.32271.4902355030043648595.stgit@dwillia2-desk3.amr.corp.intel.com> From: Sergei Shtylyov Message-ID: <07835e19-baef-81a0-b921-5bae491f03f6@cogentembedded.com> Date: Sat, 6 Jan 2018 13:05:40 +0300 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <151520107515.32271.4902355030043648595.stgit@dwillia2-desk3.amr.corp.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On 1/6/2018 4:11 AM, Dan Williams wrote: > Expectedly, static analysis reports that 'fd' is a user controlled value > that is used as a data dependency to read from the 'fdt->fd' array. In > order to avoid potential leaks of kernel memory values, block > speculative execution of the instruction stream that could issue reads > based on an invalid 'file *' returned from __fcheck_files. > > Based on an original patch by Elena Reshetova. > > Cc: Al Viro > Signed-off-by: Elena Reshetova > Signed-off-by: Dan Williams > --- > include/linux/fdtable.h | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h > index 1c65817673db..4a147c5c2533 100644 > --- a/include/linux/fdtable.h > +++ b/include/linux/fdtable.h > @@ -81,9 +81,10 @@ struct dentry; > static inline struct file *__fcheck_files(struct files_struct *files, unsigned int fd) > { > struct fdtable *fdt = rcu_dereference_raw(files->fdt); > + struct file __rcu **fdp; > > - if (fd < fdt->max_fds) > - return rcu_dereference_raw(fdt->fd[fd]); > + if ((fdp = nospec_array_ptr(fdt->fd, fd, fdt->max_fds))) And here... > + return rcu_dereference_raw(*fdp); > return NULL; > } > MMR, Sergei