linux-hardening - Re: [PATCH] pstore/platform: Add check for kstrdup

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Date:   Wed, 14 Jun 2023 12:01:30 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     tony.luck@...el.com, gpiccoli@...lia.com,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pstore/platform: Add check for kstrdup

On Wed, Jun 14, 2023 at 06:00:20PM +0800, Jiasheng Jiang wrote:
> Add check for the return value of kstrdup() and return the error
> if it fails in order to avoid NULL pointer dereference.
> 
> Fixes: 563ca40ddf40 ("pstore/platform: Switch pstore_info::name to const")
> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
> ---
>  fs/pstore/platform.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index cbc0b468c1ab..afe07f0d1216 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -631,6 +631,10 @@ int pstore_register(struct pstore_info *psi)
>  	 * through /sys/module/pstore/parameters/backend
>  	 */
>  	backend = kstrdup(psi->name, GFP_KERNEL);
> +	if (!backend) {
> +		mutex_unlock(&psinfo_lock);
> +		return -ENOMEM;
> +	}

Hmm, I think this isn't the right place since there's been a bunch of
other allocations and registrations. I think it would be better to
allocate a copy (but not assign to "backend" yet) earlier, perhaps
before the taking the psinfo_lock lock? Like:

	char *new_backend;
	...
	new_backend = kstrdup(psi->name, GFP_KERNEL);
	if (!new_backend)
		return -ENOMEM;

        mutex_lock(&psinfo_lock);
        if (psinfo) {
		...
                mutex_unlock(&psinfo_lock);
		kfree(new_backend);
                return -EBUSY;
        }
	...
	backend = new_backend;


-Kees

-- 
Kees Cook