[PATCH] i3c: replace deprecated strncpy

[PATCH] i3c: replace deprecated strncpy

[Justin Stitt]

`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@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
 drivers/i3c/master.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
index 87283e4a4607..8573ca507708 100644
--- a/drivers/i3c/master.c
+++ b/drivers/i3c/master.c
@@ -2309,7 +2309,7 @@ static int i3c_master_i2c_adapter_init(struct i3c_master_controller *master)
 	adap->dev.parent = master->dev.parent;
 	adap->owner = master->dev.parent->driver->owner;
 	adap->algo = &i3c_master_i2c_algo;
-	strncpy(adap->name, dev_name(master->dev.parent), sizeof(adap->name));
+	strscpy(adap->name, dev_name(master->dev.parent), sizeof(adap->name));
 
 	/* FIXME: Should we allow i3c masters to override these values? */
 	adap->timeout = 1000;

---
base-commit: 2cf0f715623872823a72e451243bbf555d10d032
change-id: 20230921-strncpy-drivers-i3c-master-c-d9e152a91aca

Best regards,
--
Justin Stitt <justinstitt@google.com>

Re: [PATCH] i3c: replace deprecated strncpy

[Kees Cook]

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@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Looks right to me; straight replacement.

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

-- 
Kees Cook

Re: [PATCH] i3c: replace deprecated strncpy

[Alexandre Belloni]

On Thu, 21 Sep 2023 03:51:04 +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);
> 
> [...]

Applied, thanks!

[1/1] i3c: replace deprecated strncpy
      commit: fa7726a4d9b91e0a8fb6fbbd819cd20f116f6c21

Best regards,

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com