[PATCH 10/11] staging: greybus: change strncpy() to strscpy()

Arnd Bergmann
2024-03-28T14:07:11Z

From: Arnd Bergmann <arnd@arndb.de>

gcc-10 warns about a strncpy() that does not enforce zero-termination:

In file included from include/linux/string.h:369,
from drivers/staging/greybus/fw-management.c:9:
In function 'strncpy',
inlined from 'fw_mgmt_backend_fw_update_operation' at drivers/staging/greybus/fw-management.c:306:2:
include/linux/fortify-string.h:108:30: error: '__builtin_strncpy' specified bound 10 equals destination size [-Werror=stringop-truncation]
108 | #define __underlying_strncpy __builtin_strncpy
| ^
include/linux/fortify-string.h:187:9: note: in expansion of macro '__underlying_strncpy'
187 | return __underlying_strncpy(p, q, size);
| ^~~~~~~~~~~~~~~~~~~~

For some reason, I cannot reproduce this with gcc-9 or gcc-11, so I'm not
sure what's going on. Changing it to strspy() avoids the warning. In this
case the existing check for zero-termination would fail but can be replaced
with an error check.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
This is from randconfig testing with random gcc versions, a .config to
reproduce is at https://pastebin.com/r13yezkU
---
drivers/staging/greybus/fw-management.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/greybus/fw-management.c b/drivers/staging/greybus/fw-management.c
index 3054f084d777..35bfdd5f32d2 100644
--- a/drivers/staging/greybus/fw-management.c
+++ b/drivers/staging/greybus/fw-management.c
@@ -303,13 +303,13 @@ static int fw_mgmt_backend_fw_update_operation(struct fw_mgmt *fw_mgmt,
struct gb_fw_mgmt_backend_fw_update_request request;
int ret;

- strncpy(request.firmware_tag, tag, GB_FIRMWARE_TAG_MAX_SIZE);
+ ret = strscpy(request.firmware_tag, tag, GB_FIRMWARE_TAG_MAX_SIZE);

/*
* The firmware-tag should be NULL terminated, otherwise throw error and
* fail.
*/
- if (request.firmware_tag[GB_FIRMWARE_TAG_MAX_SIZE - 1] != '\0') {
+ if (ret == -E2BIG) {
dev_err(fw_mgmt->parent, "backend-update: firmware-tag is not NULL terminated\n");
return -EINVAL;
}
--
2.39.2