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

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Message-ID: <20170312011135.GM29622@ZenIV.linux.org.uk>
Date:   Sun, 12 Mar 2017 01:11:40 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Julia Lawall <julia.lawall@...6.fr>
Cc:     simran singhal <singhalsimran0@...il.com>,
        gregkh@...uxfoundation.org, arve@...roid.com,
        riandrews@...roid.com, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, outreachy-kernel@...glegroups.com
Subject: Re: [Outreachy kernel] [PATCH] staging: android: Replace strcpy with
 strlcpy

On Sat, Mar 11, 2017 at 09:47:30PM +0100, Julia Lawall wrote:
> 
> 
> On Sun, 12 Mar 2017, 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));
> 
> There is a parenthesis in the wrong place.

Worse - moving parenthesis to just after asma->name would result in
interestingly bogus value (size + amount skipped instead of size -
amount skipped).

Folks, blind changes in name of security are seriously counterproductive;
fortunately, in this particular case overflow prevention is taken care
of by earlier code (source of strcpy is a local array of size that
isn't enough to cause trouble and it is NUL-terminated), so that
particular strlcpy() is simply pointless, but if not for that...
Variant with sizeof(asma->name) + ASHMEM_NAME_PREFIX_LEN would've
invited an overflow *and* made it harder to spot in the future -
"it uses strlcpy, no worries about overflows here"...