@p1 is assigned to @setup_buffer and then we manually assign a NUL-byte
at the first index. This renders the following strlen() call useless.
Moreover, we don't need to reassign p1 to setup_buffer for any reason --
neither do we need to manually set a NUL-byte at the end. strscpy()
resolves all this code making it easier to read.

Even considering the path where @str is falsey, the manual NUL-byte
assignment is useless as setup_buffer is declared with static storage
duration in the top-level scope which should NUL-initialize the whole
buffer.

Signed-off-by: Justin Stitt <justinstitt@google.com>
---
 drivers/scsi/wd33c93.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/scsi/wd33c93.c b/drivers/scsi/wd33c93.c
index e4fafc77bd20..a44b60c9004a 100644
--- a/drivers/scsi/wd33c93.c
+++ b/drivers/scsi/wd33c93.c
@@ -1721,9 +1721,7 @@ wd33c93_setup(char *str)
 	p1 = setup_buffer;
 	*p1 = '\0';
 	if (str)
-		strncpy(p1, str, SETUP_BUFFER_SIZE - strlen(setup_buffer));
-	setup_buffer[SETUP_BUFFER_SIZE - 1] = '\0';
-	p1 = setup_buffer;
+		strscpy(p1, str, SETUP_BUFFER_SIZE);
 	i = 0;
 	while (*p1 && (i < MAX_SETUP_ARGS)) {
 		p2 = strchr(p1, ',');

-- 
2.44.0.rc0.258.g7320e95886-goog

On Fri, 23 Feb 2024, Justin Stitt wrote:

> @p1 is assigned to @setup_buffer and then we manually assign a NUL-byte
> at the first index. This renders the following strlen() call useless.
> Moreover, we don't need to reassign p1 to setup_buffer for any reason --
> neither do we need to manually set a NUL-byte at the end. strscpy()
> resolves all this code making it easier to read.
> 
> Even considering the path where @str is falsey, the manual NUL-byte
> assignment is useless 

And yet your patch would only remove one of those assignments...

> as setup_buffer is declared with static storage
> duration in the top-level scope which should NUL-initialize the whole
> buffer.
> 

So, in order to review this patch, to try to avoid regressions, I would 
have to check your assumption that setup_buffer cannot change after being 
statically initialized. (The author of this code apparently was not 
willing to make that assumption.) It seems that patch review would require 
exhaustively searching for functions using the buffer, and examining the 
call graphs involving those functions. Is it really worth the effort?

> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
>  drivers/scsi/wd33c93.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/wd33c93.c b/drivers/scsi/wd33c93.c
> index e4fafc77bd20..a44b60c9004a 100644
> --- a/drivers/scsi/wd33c93.c
> +++ b/drivers/scsi/wd33c93.c
> @@ -1721,9 +1721,7 @@ wd33c93_setup(char *str)
>  	p1 = setup_buffer;
>  	*p1 = '\0';
>  	if (str)
> -		strncpy(p1, str, SETUP_BUFFER_SIZE - strlen(setup_buffer));
> -	setup_buffer[SETUP_BUFFER_SIZE - 1] = '\0';
> -	p1 = setup_buffer;
> +		strscpy(p1, str, SETUP_BUFFER_SIZE);
>  	i = 0;
>  	while (*p1 && (i < MAX_SETUP_ARGS)) {
>  		p2 = strchr(p1, ',');
> 
>

On Sat, Feb 24, 2024 at 10:44:12AM +1100, Finn Thain wrote:
> 
> On Fri, 23 Feb 2024, Justin Stitt wrote:
> 
> > @p1 is assigned to @setup_buffer and then we manually assign a NUL-byte
> > at the first index. This renders the following strlen() call useless.
> > Moreover, we don't need to reassign p1 to setup_buffer for any reason --
> > neither do we need to manually set a NUL-byte at the end. strscpy()
> > resolves all this code making it easier to read.
> > 
> > Even considering the path where @str is falsey, the manual NUL-byte
> > assignment is useless 
> 
> And yet your patch would only remove one of those assignments...

The first is needed in case it is called again.

> 
> > as setup_buffer is declared with static storage
> > duration in the top-level scope which should NUL-initialize the whole
> > buffer.
> > 
> 
> So, in order to review this patch, to try to avoid regressions, I would 
> have to check your assumption that setup_buffer cannot change after being 
> statically initialized. (The author of this code apparently was not 
> willing to make that assumption.) It seems that patch review would require 
> exhaustively searching for functions using the buffer, and examining the 
> call graphs involving those functions. Is it really worth the effort?

It seems to be run for each device? Regardless, I think leaving the
initial "*p1 = '\0';" solves this. (Though I fear for parallel
initializations, but that was already buggy: this code is from pre-git
history...)

> 
> > Signed-off-by: Justin Stitt <justinstitt@google.com>
> > ---
> >  drivers/scsi/wd33c93.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/drivers/scsi/wd33c93.c b/drivers/scsi/wd33c93.c
> > index e4fafc77bd20..a44b60c9004a 100644
> > --- a/drivers/scsi/wd33c93.c
> > +++ b/drivers/scsi/wd33c93.c
> > @@ -1721,9 +1721,7 @@ wd33c93_setup(char *str)
> >  	p1 = setup_buffer;
> >  	*p1 = '\0';
> >  	if (str)
> > -		strncpy(p1, str, SETUP_BUFFER_SIZE - strlen(setup_buffer));
> > -	setup_buffer[SETUP_BUFFER_SIZE - 1] = '\0';
> > -	p1 = setup_buffer;
> > +		strscpy(p1, str, SETUP_BUFFER_SIZE);
> >  	i = 0;
> >  	while (*p1 && (i < MAX_SETUP_ARGS)) {
> >  		p2 = strchr(p1, ',');
> > 
> > 

I think this conversion looks right.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook