[PATCH v3] soc: qcom: cmd-db: replace deprecated strncpy with strtomem

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strncpy() is an ambiguous and potentially dangerous interface [1]. We
should prefer more robust and less ambiguous alternatives.

@query is marked as __nonstring and doesn't need to be NUL-terminated.

Since we are doing a string to memory copy, we can use the aptly named
"strtomem" -- specifically, the "pad" variant to also ensure NUL-padding
throughout the destination buffer.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@xxxxxxxxxxxxxxx
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
Changes in v3:
- Prefer strtomem_pad (thanks Bjorn)
- Reword commit message (thanks Bjorn)
- Carry over Kees' RB as this new version is functionally the same and
  matches the same spirit of v2
- Link to v2: https://lore.kernel.org/r/20240318-strncpy-drivers-soc-qcom-cmd-db-c-v2-1-8f6ebf1bd891@xxxxxxxxxx

Changes in v2:
- use strtomem instead of memcpy (thanks Kees)
- Link to v1: https://lore.kernel.org/r/20240314-strncpy-drivers-soc-qcom-cmd-db-c-v1-1-70f5d5e70732@xxxxxxxxxx
Note: build-tested only.

Found with: $ rg "strncpy\("
 drivers/soc/qcom/cmd-db.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/drivers/soc/qcom/cmd-db.c b/drivers/soc/qcom/cmd-db.c
index a5fd68411bed..d51ae99d9c02 100644
--- a/drivers/soc/qcom/cmd-db.c
+++ b/drivers/soc/qcom/cmd-db.c
@@ -147,12 +147,7 @@ static int cmd_db_get_header(const char *id, const struct entry_header **eh,
 	if (ret)
 		return ret;
-	/*
-	 * 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));
+	strtomem_pad(query, id, 0);
 	for (i = 0; i < MAX_SLV_ID; i++) {
 		rsc_hdr = &cmd_db_header->header[i];

base-commit: fe46a7dd189e25604716c03576d05ac8a5209743
change-id: 20240314-strncpy-drivers-soc-qcom-cmd-db-c-284f3abaabb8

Best regards,
Justin Stitt <justinstitt@xxxxxxxxxx>

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