[PATCH] soc: qcom: cmd-db: replace strscpy_pad() with strncpy()

[PATCH] soc: qcom: cmd-db: replace strscpy_pad() with strncpy()

[Douglas Anderson]

Commit ac0126a01735 ("soc: qcom: cmd-db: replace strncpy() with
strscpy_pad()") breaks booting on my sc7280-herobrine-herobrine
device. From printouts I see that at bootup the function is called
with an id of "lnbclka2" which is 8 bytes big.

Previously all 8 bytes of this string were copied to the
destination. Now only 7 bytes will be copied since strscpy_pad() saves
a byte for '\0' termination.

We don't need the '\0' termination in the destination. Let's go back
to strncpy(). According to the warning:
  If a caller is using non-NUL-terminated strings, strncpy() can still
  be used, but destinations should be marked with the __nonstring
  attribute to avoid future compiler warnings.
...so we'll do that.

Fixes: ac0126a01735 ("soc: qcom: cmd-db: replace strncpy() with strscpy_pad()")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

 drivers/soc/qcom/cmd-db.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
index c5137c25d819..0aafe90277bc 100644
--- a/drivers/soc/qcom/cmd-db.c
+++ b/drivers/soc/qcom/cmd-db.c
@@ -141,14 +141,14 @@ static int cmd_db_get_header(const char *id, const struct entry_header **eh,
 	const struct rsc_hdr *rsc_hdr;
 	const struct entry_header *ent;
 	int ret, i, j;
-	u8 query[8];
+	u8 query[8] __nonstring;
 
 	ret = cmd_db_ready();
 	if (ret)
 		return ret;
 
 	/* Pad out query string to same length as in DB */
-	strscpy_pad(query, id, sizeof(query));
+	strncpy(query, id, sizeof(query));
 
 	for (i = 0; i < MAX_SLV_ID; i++) {
 		rsc_hdr = &cmd_db_header->header[i];
-- 
2.37.0.rc0.161.g10f37bed90-goog

Re: [PATCH] soc: qcom: cmd-db: replace strscpy_pad() with strncpy()

[Matthias Kaehlcke]

On Mon, Jun 27, 2022 at 04:17:00PM -0700, Douglas Anderson wrote:
> Commit ac0126a01735 ("soc: qcom: cmd-db: replace strncpy() with
> strscpy_pad()") breaks booting on my sc7280-herobrine-herobrine
> device. From printouts I see that at bootup the function is called
> with an id of "lnbclka2" which is 8 bytes big.
> 
> Previously all 8 bytes of this string were copied to the
> destination. Now only 7 bytes will be copied since strscpy_pad() saves
> a byte for '\0' termination.
> 
> We don't need the '\0' termination in the destination. Let's go back
> to strncpy(). According to the warning:
>   If a caller is using non-NUL-terminated strings, strncpy() can still
>   be used, but destinations should be marked with the __nonstring
>   attribute to avoid future compiler warnings.
> ...so we'll do that.
> 
> Fixes: ac0126a01735 ("soc: qcom: cmd-db: replace strncpy() with strscpy_pad()")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>

Re: [PATCH] soc: qcom: cmd-db: replace strscpy_pad() with strncpy()

[Stephen Boyd]

Quoting Douglas Anderson (2022-06-27 16:17:00)
> Commit ac0126a01735 ("soc: qcom: cmd-db: replace strncpy() with
> strscpy_pad()") breaks booting on my sc7280-herobrine-herobrine
> device. From printouts I see that at bootup the function is called
> with an id of "lnbclka2" which is 8 bytes big.
> 
> Previously all 8 bytes of this string were copied to the
> destination. Now only 7 bytes will be copied since strscpy_pad() saves
> a byte for '\0' termination.
> 
> We don't need the '\0' termination in the destination. Let's go back
> to strncpy(). According to the warning:
>   If a caller is using non-NUL-terminated strings, strncpy() can still
>   be used, but destinations should be marked with the __nonstring
>   attribute to avoid future compiler warnings.
> ...so we'll do that.
> 
> Fixes: ac0126a01735 ("soc: qcom: cmd-db: replace strncpy() with strscpy_pad()")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> 
>  drivers/soc/qcom/cmd-db.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
> index c5137c25d819..0aafe90277bc 100644
> --- a/drivers/soc/qcom/cmd-db.c
> +++ b/drivers/soc/qcom/cmd-db.c
> @@ -141,14 +141,14 @@ static int cmd_db_get_header(const char *id, const struct entry_header **eh,
>         const struct rsc_hdr *rsc_hdr;
>         const struct entry_header *ent;
>         int ret, i, j;
> -       u8 query[8];
> +       u8 query[8] __nonstring;

Since you're already here, can you change 8 to be sizeof(ent->id)? That
would directly tie the two lengths together so that one can't change and
then the carefully crafted strncpy() fails again.

>  
>         ret = cmd_db_ready();
>         if (ret)
>                 return ret;
>  
>         /* Pad out query string to same length as in DB */
> -       strscpy_pad(query, id, sizeof(query));
> +       strncpy(query, id, sizeof(query));