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[198.0.35.241]) by smtp.gmail.com with ESMTPSA id i2-20020a170902c94200b001b81a97860asm2340421pla.27.2023.09.14.20.36.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 Sep 2023 20:36:16 -0700 (PDT) Date: Thu, 14 Sep 2023 20:36:15 -0700 From: Kees Cook To: Justin Stitt Cc: Stuart Yoder , Laurentiu Tudor , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] bus: fsl-mc: refactor deprecated strncpy Message-ID: <202309142034.2B1DC7DE51@keescook> References: <20230912-strncpy-drivers-bus-fsl-mc-dprc-c-v1-1-cdb56aa3f4f4@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230912-strncpy-drivers-bus-fsl-mc-dprc-c-v1-1-cdb56aa3f4f4@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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-hardening@vger.kernel.org > Cc: Kees Cook > Signed-off-by: Justin Stitt > --- > 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 -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 > -- Kees Cook