linux-kernel - Re: [PATCH][next] powerpc/vas: Fix potential NULL pointer dereference

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Date:   Mon, 18 Oct 2021 16:26:12 -0500
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Tyrel Datwyler <tyreld@...ux.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Haren Myneni <haren@...ux.ibm.com>,
        linux-hardening@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] powerpc/vas: Fix potential NULL pointer dereference

On Mon, Oct 18, 2021 at 02:09:31PM -0700, Tyrel Datwyler wrote:
> On 10/14/21 10:03 PM, Gustavo A. R. Silva wrote:
> > (!ptr && !ptr->foo) strikes again. :)
> > 
> > The expression (!ptr && !ptr->foo) is bogus and in case ptr is NULL,
> > it leads to a NULL pointer dereference: ptr->foo.
> > 
> > Fix this by converting && to ||
> > 
> > This issue was detected with the help of Coccinelle, and audited and
> > fixed manually.
> > 
> > Fixes: 1a0d0d5ed5e3 ("powerpc/vas: Add platform specific user window operations")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> Looking at the usage pattern it is obvious that if we determine !ptr attempting
> to also confirm !ptr->ops is going to blow up.
> 
> LGTM.
> 
> Reviewed-by: Tyrel Datwyler <tyreld@...ux.ibm.com>

Thanks, Tyrel.
--
Gustavo

> 
> > ---
> >  arch/powerpc/platforms/book3s/vas-api.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/powerpc/platforms/book3s/vas-api.c b/arch/powerpc/platforms/book3s/vas-api.c
> > index 30172e52e16b..4d82c92ddd52 100644
> > --- a/arch/powerpc/platforms/book3s/vas-api.c
> > +++ b/arch/powerpc/platforms/book3s/vas-api.c
> > @@ -303,7 +303,7 @@ static int coproc_ioc_tx_win_open(struct file *fp, unsigned long arg)
> >  		return -EINVAL;
> >  	}
> > 
> > -	if (!cp_inst->coproc->vops && !cp_inst->coproc->vops->open_win) {
> > +	if (!cp_inst->coproc->vops || !cp_inst->coproc->vops->open_win) {
> >  		pr_err("VAS API is not registered\n");
> >  		return -EACCES;
> >  	}
> > @@ -373,7 +373,7 @@ static int coproc_mmap(struct file *fp, struct vm_area_struct *vma)
> >  		return -EINVAL;
> >  	}
> > 
> > -	if (!cp_inst->coproc->vops && !cp_inst->coproc->vops->paste_addr) {
> > +	if (!cp_inst->coproc->vops || !cp_inst->coproc->vops->paste_addr) {
> >  		pr_err("%s(): VAS API is not registered\n", __func__);
> >  		return -EACCES;
> >  	}
> > 
>