linux-kernel - Re: [PATCH] staging: android: Replace strcpy with strlcpy

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Message-ID: <CALrZqyNS57uz5nKxVw-1msRvum1L0Qj8f=D5wPr8X1GVq25nZA@mail.gmail.com>
Date:   Mon, 13 Mar 2017 18:44:23 +0530
From:   SIMRAN SINGHAL <singhalsimran0@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, devel@...verdev.osuosl.org,
        outreachy-kernel <outreachy-kernel@...glegroups.com>,
        arve@...roid.com, riandrews@...roid.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: android: Replace strcpy with strlcpy

On Mon, Mar 13, 2017 at 6:27 PM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
> On Mon, Mar 13, 2017 at 06:17:22PM +0530, SIMRAN SINGHAL wrote:
>> On Mon, Mar 13, 2017 at 6:11 PM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
>> > On Sun, Mar 12, 2017 at 02:10:01AM +0530, simran singhal wrote:
>> >> Replace strcpy with strlcpy as strcpy does not check for buffer
>> >> overflow.
>> >> This is found using Flawfinder.
>> >>
>> >> Signed-off-by: simran singhal <singhalsimran0@...il.com>
>> >> ---
>> >>  drivers/staging/android/ashmem.c | 3 ++-
>> >>  1 file changed, 2 insertions(+), 1 deletion(-)
>> >>
>> >> diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
>> >> index 7cbad0d..eb2f4ef 100644
>> >> --- a/drivers/staging/android/ashmem.c
>> >> +++ b/drivers/staging/android/ashmem.c
>> >> @@ -548,7 +548,8 @@ static int set_name(struct ashmem_area *asma, void __user *name)
>> >>       if (unlikely(asma->file))
>> >>               ret = -EINVAL;
>> >>       else
>> >> -             strcpy(asma->name + ASHMEM_NAME_PREFIX_LEN, local_name);
>> >> +             strlcpy(asma->name + ASHMEM_NAME_PREFIX_LEN, local_name,
>> >> +                     sizeof(asma->name + ASHMEM_NAME_PREFIX_LEN));
>> >                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>> > This isn't right.
>> >
>> > Also please do some analysis to see if it's a real bug or a false
>> > positive.  It is a false positive in this case.
>> >
>>
>> Dan,
>> I have already sent v3 of this in which I have used:
>> sizeof(asma->name) - ASHMEM_NAME_PREFIX_LEN
>
> Yeah.  I saw that.  It's fine, I suppose but you should have done more
> analysis to see if it was a real bug like Al and Greg suggested.  The
> changelog should say something like:
>
> "The destination buffer is 12345 bytes long but we're copying a 10000
> character string so it can overflow."  Occasionally, I will fudge a
> little bit on these changelogs to say that I have looked every where to
> determine the size of the source buffer and can't figure it out so this
> change makes it easier to audit.  But I try to figure it out generally.
>
> Really tools should be able to show that this code is safe.  They
> currently don't so far as I know, but they should.  It's a matter of
> waiting a year for Smatch to improve.
>

Thanks!

Will keep this in mind.

> regards,
> dan carpenter
>