[PATCH v3] 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.

While we're at it, let's change the query array to use
"sizeof(ent->id)" so it can't possibly go out of sync with our later
copy.

Fixes: ac0126a01735 ("soc: qcom: cmd-db: replace strncpy() with strscpy_pad()")
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
Reviewed-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
---

Changes in v3:
- Add comment that query isn't necessarily '\0' terminated.

Changes in v2:
- Size array with "sizeof(ent->id)"

 drivers/soc/qcom/cmd-db.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
index c5137c25d819..629a7188b576 100644
--- a/drivers/soc/qcom/cmd-db.c
+++ b/drivers/soc/qcom/cmd-db.c
@@ -141,14 +141,18 @@ 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[sizeof(ent->id)] __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));
+	/*
+	 * Pad out query string to same length as in DB. NOTE: the output
+	 * query string is not necessarily '\0' terminated if it bumps up
+	 * against the max size. That's OK and expected.
+	 */
+	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