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

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Date:   Mon, 18 Oct 2021 14:09:31 -0700
From:   Tyrel Datwyler <tyreld@...ux.ibm.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        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>
Cc:     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 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>

> ---
>  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;
>  	}
>