`strncpy` is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.
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: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
---
Note: build-tested only.
---
drivers/misc/ibmvmc.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/drivers/misc/ibmvmc.c b/drivers/misc/ibmvmc.c
index 2101eb12bcba..6d9ed9325f9f 100644
--- a/drivers/misc/ibmvmc.c
+++ b/drivers/misc/ibmvmc.c
@@ -1249,9 +1249,7 @@ static long ibmvmc_ioctl_sethmcid(struct ibmvmc_file_session *session,
return -EIO;
}
- /* Make sure buffer is NULL terminated before trying to print it */
- memset(print_buffer, 0, HMC_ID_LEN + 1);
- strncpy(print_buffer, hmc->hmc_id, HMC_ID_LEN);
+ strscpy(print_buffer, hmc->hmc_id, sizeof(print_buffer));
pr_info("ibmvmc: sethmcid: Set HMC ID: \"%s\"\n", print_buffer);
memcpy(buffer->real_addr_local, hmc->hmc_id, HMC_ID_LEN);
---
base-commit: 6465e260f48790807eef06b583b38ca9789b6072
change-id: 20230927-strncpy-drivers-misc-ibmvmc-c-534349716fa4
Best regards,
--
Justin Stitt <[email protected]>
On Wed, Sep 27, 2023 at 05:52:14AM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
>
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on the destination buffer without
> unnecessarily NUL-padding.
This is weird -- I think hmc_id needs to be marked __nonstring, and the
commit log should talk about how it appears to be not %NUL terminated.
The bounce buffer is weird -- it seems like hmc_id could be made a
regular C string by being changed to MHC_ID_LEN + 1, and then everything
would work correctly without needing a bounce buffer, etc. (Well, it
would need explicit %NUL termination after the copy_from_user()).
But if that refactor doesn't sound right to maintainers, then I'd agree
that this patch is fine (though capturing the __nonstring bit might be
nice):
Reviewed-by: Kees Cook <[email protected]>
-Kees
>
> 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/misc/ibmvmc.c | 4 +---
> 1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/misc/ibmvmc.c b/drivers/misc/ibmvmc.c
> index 2101eb12bcba..6d9ed9325f9f 100644
> --- a/drivers/misc/ibmvmc.c
> +++ b/drivers/misc/ibmvmc.c
> @@ -1249,9 +1249,7 @@ static long ibmvmc_ioctl_sethmcid(struct ibmvmc_file_session *session,
> return -EIO;
> }
>
> - /* Make sure buffer is NULL terminated before trying to print it */
> - memset(print_buffer, 0, HMC_ID_LEN + 1);
> - strncpy(print_buffer, hmc->hmc_id, HMC_ID_LEN);
> + strscpy(print_buffer, hmc->hmc_id, sizeof(print_buffer));
> pr_info("ibmvmc: sethmcid: Set HMC ID: \"%s\"\n", print_buffer);
>
> memcpy(buffer->real_addr_local, hmc->hmc_id, HMC_ID_LEN);
>
> ---
> base-commit: 6465e260f48790807eef06b583b38ca9789b6072
> change-id: 20230927-strncpy-drivers-misc-ibmvmc-c-534349716fa4
>
> Best regards,
> --
> Justin Stitt <[email protected]>
>
--
Kees Cook