2023-09-13 23:14:17

by Justin Stitt

Subject: [PATCH] dax: refactor deprecated strncpy

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

We should prefer more robust and less ambiguous string interfaces.

`dax_id->dev_name` is expected to be NUL-terminated and has been zero-allocated.

A suitable replacement is `strscpy` [2] due to the fact that it
guarantees NUL-termination on the destination buffer. Moreover, due to
`dax_id` being zero-allocated the padding behavior of `strncpy` is not
needed and a simple 1:1 replacement of strncpy -> strscpy should
suffice.

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: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
---
Note: build-tested only.
---
drivers/dax/bus.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
index 0ee96e6fc426..1659b787b65f 100644
--- a/drivers/dax/bus.c
+++ b/drivers/dax/bus.c
@@ -103,7 +103,7 @@ static ssize_t do_id_store(struct device_driver *drv, const char *buf,
if (action == ID_ADD) {
dax_id = kzalloc(sizeof(*dax_id), GFP_KERNEL);
if (dax_id) {
- strncpy(dax_id->dev_name, buf, DAX_NAME_LEN);
+ strscpy(dax_id->dev_name, buf, DAX_NAME_LEN);
list_add(&dax_id->list, &dax_drv->ids);
} else
rc = -ENOMEM;

---
base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
change-id: 20230913-strncpy-drivers-dax-bus-c-f12e3153e44b

Best regards,
--
Justin Stitt <[email protected]>

2023-09-15 12:15:04

by Kees Cook

Subject: Re: [PATCH] dax: refactor deprecated strncpy

On Wed, Sep 13, 2023 at 01:10:24AM +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.
>
> `dax_id->dev_name` is expected to be NUL-terminated and has been zero-allocated.
>
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on the destination buffer. Moreover, due to
> `dax_id` being zero-allocated the padding behavior of `strncpy` is not
> needed and a simple 1:1 replacement of strncpy -> strscpy should
> suffice.
>
> 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: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>

Looks correct to me.

Reviewed-by: Kees Cook <[email protected]>

--
Kees Cook