From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:44595 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750757AbeCPEdN (ORCPT ); Fri, 16 Mar 2018 00:33:13 -0400 Subject: Re: [PATCH 13/16] bcache: Make bch_dump_read() fail if copying to user space fails To: Bart Van Assche , "mlyle@lyle.org" , "kent.overstreet@gmail.com" Cc: "hch@lst.de" , "linux-bcache@vger.kernel.org" , "linux-block@vger.kernel.org" References: <20180315150814.9412-1-bart.vanassche@wdc.com> <20180315150814.9412-14-bart.vanassche@wdc.com> <1521133564.2834.10.camel@wdc.com> From: Coly Li Message-ID: Date: Fri, 16 Mar 2018 12:33:01 +0800 MIME-Version: 1.0 In-Reply-To: <1521133564.2834.10.camel@wdc.com> Content-Type: text/plain; charset=utf-8 Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On 16/03/2018 1:06 AM, Bart Van Assche wrote: > On Fri, 2018-03-16 at 01:00 +0800, Coly Li wrote: >> On 15/03/2018 11:08 PM, Bart Van Assche wrote: >>> copy_to_user() returns the number of remaining bytes. Avoid that >>> a larger value is returned than the number of bytes that have >>> been copied by returning -EFAULT if not all bytes have been copied. >>> >>> Signed-off-by: Bart Van Assche >>> --- >>> drivers/md/bcache/debug.c | 5 ++--- >>> 1 file changed, 2 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/md/bcache/debug.c b/drivers/md/bcache/debug.c >>> index af89408befe8..376899cfcbf1 100644 >>> --- a/drivers/md/bcache/debug.c >>> +++ b/drivers/md/bcache/debug.c >>> @@ -175,9 +175,8 @@ static ssize_t bch_dump_read(struct file *file, char __user *buf, >>> struct keybuf_key *w; >>> unsigned bytes = min(i->bytes, size); >>> >>> - int err = copy_to_user(buf, i->buf, bytes); >>> - if (err) >>> - return err; >>> + if (copy_to_user(buf, i->buf, bytes)) >>> + return -EFAULT; >>> >> >> Hi Bart, >> >> I am not sure whether this change is correct. -EFAULT seems not an >> expected return value of read(2), while -1 is the expected return value >> when error occurs. >> >> Maybe if copy_to_user() returns value in (0, size], "ret + (size - err)" >> should be returned. An exception is when copy_to_user() returns 0 and >> ret is 0 too, in this situation -1 should be returned. >> >> Correct me if I am wrong. > > Hello Coly, > > I'm not familiar enough with bcache to provide the answer to your question so > I will drop this patch from this series. Hi Bart, It seems you catch a code bug here. I will look into this and handle it here. Thanks for the hint :-) Coly Li