linux-hardening - Re: [PATCH] i3c: replace deprecated strncpy

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Date: Sat, 23 Sep 2023 20:04:38 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Alexandre Belloni <alexandre.belloni@...tlin.com>,
	linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] i3c: replace deprecated strncpy

On Thu, Sep 21, 2023 at 03:51:04AM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> We expect adap->name to be NUL-terminated based on i2c_adapter name use:
> | dev_dbg(&adap->dev, "adapter [%s] registered\n", adap->name);
> 
> NUL-padding does not seem to be required as `master` is zero-allocated
> and `i3c_master_to_i2c_adapter` simply returns a field from within
> `master`:
> |       master = devm_kzalloc(dev, sizeof(*master), GFP_KERNEL);
> ...
> |      	struct i2c_adapter *adap = i3c_master_to_i2c_adapter(master);
> ...
> |       static struct i2c_adapter *
> |       i3c_master_to_i2c_adapter(struct i3c_master_controller *master)
> |       {
> |       	return &master->i2c;
> |       }
> 
> This means that `adap->name` should already be filled with NUL-bytes.
> 
> Considering the above, a suitable replacement is `strscpy` [2] due to
> the fact that it guarantees NUL-termination on the destination buffer
> without unnecessarily NUL-padding.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Looks right to me; straight replacement.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook