Re: [PATCH] floppy: fix usercopy direction

From: Alexander Popov <alex.popov@linux.com>
To: Julia Lawall <julia.lawall@lip6.fr>, Jann Horn <jannh@google.com>
Cc: Jens Axboe <axboe@kernel.dk>, Jiri Kosina <jikos@kernel.org>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	Al Viro <viro@zeniv.linux.org.uk>,
	Mukesh Ojha <mojha@codeaurora.org>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>,
	Denis Efremov <efremov@linux.com>,
	Gilles Muller <Gilles.Muller@lip6.fr>,
	Nicolas Palix <nicolas.palix@imag.fr>,
	Michal Marek <michal.lkml@markovi.net>,
	cocci@systeme.lip6.fr
Subject: Re: [PATCH] floppy: fix usercopy direction
Date: Fri, 9 Aug 2019 18:05:17 +0300	[thread overview]
Message-ID: <3ee24295-6d63-6da9-774f-f1a599418685@linux.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1908091555090.2946@hadrien>

On 09.08.2019 16:56, Julia Lawall wrote:
> On Fri, 9 Aug 2019, Alexander Popov wrote:
>> On 27.03.2019 1:03, Jann Horn wrote:
>>> As sparse points out, these two copy_from_user() should actually be
>>> copy_to_user().
>>
>> I also wrote a coccinelle rule for detecting similar bugs (adding coccinelle
>> experts to CC).
>>
>>
>> virtual report
>>
>> @cfu@
> 
> You can replace the above line with @cfu exists@.  You want to find the
> existence of such a call, not ensure that the call occurs on every
> control-flow path, which is the default.

Thanks Julia, I see `exists` allows to drop `<+ +>`, right?

> Do you want this rule to go into the kernel?

It turned out that sparse already can find these bugs.
Is this rule useful anyway? If so, I can prepare a patch.

>> identifier f;
>> type t;
>> identifier v;
>> position decl_p;
>> position copy_p;
>> @@
>>
>> f(..., t v@decl_p, ...)
>> {
>> <+...
>> copy_from_user@copy_p(v, ...)
>> ...+>
>> }
>>
>> @script:python@
>> f << cfu.f;
>> t << cfu.t;
>> v << cfu.v;
>> decl_p << cfu.decl_p;
>> copy_p << cfu.copy_p;
>> @@
>>
>> if '__user' in t:
>>   msg0 = "function \"" + f + "\" has arg \"" + v + "\" of type \"" + t + "\""
>>   coccilib.report.print_report(decl_p[0], msg0)
>>   msg1 = "copy_from_user uses \"" + v + "\" as the destination. What a shame!\n"
>>   coccilib.report.print_report(copy_p[0], msg1)
>>
>>
>> The rule output:
>>
>> ./drivers/block/floppy.c:3756:49-52: function "compat_getdrvprm" has arg "arg"
>> of type "struct compat_floppy_drive_params __user *"
>> ./drivers/block/floppy.c:3783:5-19: copy_from_user uses "arg" as the
>> destination. What a shame!
>>
>> ./drivers/block/floppy.c:3789:49-52: function "compat_getdrvstat" has arg "arg"
>> of type "struct compat_floppy_drive_struct __user *"
>> ./drivers/block/floppy.c:3819:5-19: copy_from_user uses "arg" as the
>> destination. What a shame!