linux-kernel - Re: [PATCH v3] fs/fcntl: restore checking against COMPAT_LOFF_T_MAX for F

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Date:   Wed, 15 Nov 2017 00:22:31 +0300
From:   Vitaly Lipatov <lav@...rsoft.ru>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     wine-patches <wine-patches@...ehq.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3] fs/fcntl: restore checking against COMPAT_LOFF_T_MAX
 for F_GETLK64

Jeff Layton писал 14.11.17 23:19:
> On Tue, 2017-11-14 at 22:25 +0300, Vitaly Lipatov wrote:
>> Jeff Layton писал 14.11.17 22:12:
>> ...
>> > Wait...
>> >
>> > Does this do anything at all in the case where you pass in
>> > COMPAT_LOFF_T_MAX? l_start and l_len are either off_t or loff_t
>> > (depending on arch).
>> >
>> > Either one will fit in the F_GETLK64/F_OFD_GETLK struct, so I don't see
>> > a need to check here.
>> 
>> I am not sure, can off_t be bigger than loff_t ?
> 
> I don't think so, at least not in any possible situation we care about
> here.
We have this checking for ages:
			if (f.l_start > COMPAT_LOFF_T_MAX)
  				ret = -EOVERFLOW;
http://debian.securedservers.com/kernel/pub/linux/kernel/people/akpm/patches/2.6/2.6.15-rc5/2.6.15-rc5-mm1/broken-out/fix-overflow-tests-for-compat_sys_fcntl64-locking.patch

> 
>> If not, we have just skip checking against COMPAT_LOFF_T_MAX.
>> 
>> ...
>> > > @@ -644,7 +644,7 @@ COMPAT_SYSCALL_DEFINE3(fcntl64, unsigned int, fd,
>> > > unsigned int, cmd,
>> > >  		err = fcntl_getlk(f.file, convert_fcntl_cmd(cmd), &flock);
>> > >  		if (err)
>> > >  			break;
>> > > -		err = fixup_compat_flock(&flock);
>> > > +		err = fixup_compat_flock(&flock, COMPAT_LOFF_T_MAX);
>> > >  		if (err)
>> > >  			return err;
>> > >  		err = put_compat_flock64(&flock, compat_ptr(arg));
>> >
>> > Maybe a simpler fix would be to just remove the fixup_compat_flock call
>> > above?
>> >
> 
> Ok. If you have a test for this, mind testing and sending a patch?
I think if COMPAT_LOFF_T_MAX is exists, that value can be smaller than 
can fit in off_t.
Checking against COMPAT_LOFF_T_MAX keep old logic works for me last 10 
years.

I have some tests around wine project I worked on. May be later I will 
do additional tests.

-- 
С уважением,
Виталий Липатов,
Etersoft