On Tue, Sep 12, 2023 at 10:52:04PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
>
> We need to prefer more robust and less ambiguous string interfaces.
>
> `obj_desc->(type|label)` are expected to be NUL-terminated strings as
> per "include/linux/fsl/mc.h +143"
> | ...
> | * struct fsl_mc_obj_desc - Object descriptor
> | * @type: Type of object: NULL terminated string
> | ...
>
> It seems `cmd_params->obj_type` is also expected to be a NUL-terminated
> string.
>
> A suitable replacement is `strscpy_pad` due to the fact that it
> guarantees NUL-termination on the destination buffer whilst keeping the
> NUL-padding behavior that `strncpy` provides.
I see evidence that %NUL padding isn't needed, like this:
/*
* Mark the obj entry as "invalid", by using the
* empty string as obj type:
*/
obj_desc->type[0] = '\0';
but there's little harm in being conservative and leaving the padding
in.
>
> Padding may not strictly be necessary but let's opt to keep it as this
> ensures no functional change.
>
> Link:
> https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
> [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-harden...@vger.kernel.org
> Cc: Kees Cook <keesc...@chromium.org>
> Signed-off-by: Justin Stitt <justinst...@google.com>
> ---
> Note: build-tested
> ---
> drivers/bus/fsl-mc/dprc.c | 12 ++++--------
> 1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/bus/fsl-mc/dprc.c b/drivers/bus/fsl-mc/dprc.c
> index d129338b8bc0..dd1b5c0fb7e2 100644
> --- a/drivers/bus/fsl-mc/dprc.c
> +++ b/drivers/bus/fsl-mc/dprc.c
> @@ -450,10 +450,8 @@ int dprc_get_obj(struct fsl_mc_io *mc_io,
> obj_desc->ver_major = le16_to_cpu(rsp_params->version_major);
> obj_desc->ver_minor = le16_to_cpu(rsp_params->version_minor);
> obj_desc->flags = le16_to_cpu(rsp_params->flags);
> - strncpy(obj_desc->type, rsp_params->type, 16);
> - obj_desc->type[15] = '\0';
> - strncpy(obj_desc->label, rsp_params->label, 16);
> - obj_desc->label[15] = '\0';
> + strscpy_pad(obj_desc->type, rsp_params->type, 16);
> + strscpy_pad(obj_desc->label, rsp_params->label, 16);
I really don't like all the open-coded sizes, but yeah, okay, it's not
technically wrong. :)
Reviewed-by: Kees Cook <keesc...@chromium.org>
-Kees
> return 0;
> }
> EXPORT_SYMBOL_GPL(dprc_get_obj);
> @@ -491,8 +489,7 @@ int dprc_set_obj_irq(struct fsl_mc_io *mc_io,
> cmd_params->irq_addr = cpu_to_le64(irq_cfg->paddr);
> cmd_params->irq_num = cpu_to_le32(irq_cfg->irq_num);
> cmd_params->obj_id = cpu_to_le32(obj_id);
> - strncpy(cmd_params->obj_type, obj_type, 16);
> - cmd_params->obj_type[15] = '\0';
> + strscpy_pad(cmd_params->obj_type, obj_type, 16);
>
> /* send command to mc*/
> return mc_send_command(mc_io, &cmd);
> @@ -564,8 +561,7 @@ int dprc_get_obj_region(struct fsl_mc_io *mc_io,
> cmd_params = (struct dprc_cmd_get_obj_region *)cmd.params;
> cmd_params->obj_id = cpu_to_le32(obj_id);
> cmd_params->region_index = region_index;
> - strncpy(cmd_params->obj_type, obj_type, 16);
> - cmd_params->obj_type[15] = '\0';
> + strscpy_pad(cmd_params->obj_type, obj_type, 16);
>
> /* send command to mc*/
> err = mc_send_command(mc_io, &cmd);
>
> ---
> base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> change-id: 20230912-strncpy-drivers-bus-fsl-mc-dprc-c-bc7d818386ec
>
> Best regards,
> --
> Justin Stitt <justinst...@google.com>
>
--
Kees Cook
