Re: [PATCH 6/6] scsi: Check sense buffer size at build time

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello!

On 5/22/2018 9:15 PM, Kees Cook wrote:

> To avoid introducing problems like those fixed in commit f7068114d45e
> ("sr: pass down correctly sized SCSI sense buffer"), this creates a macro
> wrapper for scsi_execute() that verifies the size of the sense buffer
> similar to what was done for command string sizes in commit 3756f6401c30
> ("exec: avoid gcc-8 warning for get_task_comm").
> 
> Another solution could be to add another argument to scsi_execute(),
> but this function already takes a lot of arguments and Jens was not fond
> of that approach. As there was only a pair of dynamically allocated sense
> buffers, this also moves those 96 bytes onto the stack to avoid triggering
> the sizeof() check.
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>   drivers/scsi/scsi_lib.c    |  6 +++---
>   include/scsi/scsi_device.h | 12 +++++++++++-
>   2 files changed, 14 insertions(+), 4 deletions(-)
> 
[...]
> diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
> index 7ae177c8e399..1bb87b6c0ad2 100644
> --- a/include/scsi/scsi_device.h
> +++ b/include/scsi/scsi_device.h
> @@ -426,11 +426,21 @@ extern const char *scsi_device_state_name(enum scsi_device_state);
>   extern int scsi_is_sdev_device(const struct device *);
>   extern int scsi_is_target_device(const struct device *);
>   extern void scsi_sanitize_inquiry_string(unsigned char *s, int len);
> -extern int scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
> +extern int __scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
>   			int data_direction, void *buffer, unsigned bufflen,
>   			unsigned char *sense, struct scsi_sense_hdr *sshdr,
>   			int timeout, int retries, u64 flags,
>   			req_flags_t rq_flags, int *resid);
> +/* Make sure any sense buffer is the correct size. */
> +#define scsi_execute(sdev, cmd, data_direction, buffer, bufflen, sense,	\
> +		     sshdr, timeout, retries, flags, rq_flags, resid)	\
> +({									\
> +	BUILD_BUG_ON((sense) != NULL &&					\
> +		     sizeof(sense) != SCSI_SENSE_BUFFERSIZE);		\

    This would only check the size of the 'sense' pointer, no?

> +	__scsi_execute(sdev, cmd, data_direction, buffer, bufflen,	\
> +		       sense, sshdr, timeout, retries, flags, rq_flags,	\
> +		       resid);						\
> +})
>   static inline int scsi_execute_req(struct scsi_device *sdev,
>   	const unsigned char *cmd, int data_direction, void *buffer,
>   	unsigned bufflen, struct scsi_sense_hdr *sshdr, int timeout,

MBR, Sergei