[greybus-dev] Re: [PATCH] greybus: firmware: use strscpy, fix tag size

On Tue, Jun 17, 2025 at 6:46 PM Greg KH gregkh@linuxfoundation.org wrote:

On Tue, Jun 17, 2025 at 06:21:37PM +0530, Pranav Tyagi wrote:

...

Increase the size of firmware_tag arrays in the following structs from GB_FIRMWARE_U_TAG_MAX_SIZE to GB_FIRMWARE_U_TAG_MAX_SIZE + 1 to accommodate null termination: - fw_mgmt_ioc_intf_load_and_validate - fw_mgmt_ioc_get_backend_version - fw_mgmt_ioc_backend_fw_update - fw_mgmt_ioc_get_intf_version

Replace strncpy() with strscpy() to ensure proper null termination as firmware_tag is interpreted as a null-terminated string and printed with %s.

Signed-off-by: Pranav Tyagi pranav.tyagi03@gmail.com

.../greybus/Documentation/firmware/firmware.c | 12 ++++++------ drivers/staging/greybus/greybus_firmware.h | 8 ++++---- 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/staging/greybus/Documentation/firmware/firmware.c b/drivers/staging/greybus/Documentation/firmware/firmware.c index 765d69faa9cc..3b4061f4b34a 100644 --- a/drivers/staging/greybus/Documentation/firmware/firmware.c +++ b/drivers/staging/greybus/Documentation/firmware/firmware.c @@ -63,8 +63,8 @@ static int update_intf_firmware(int fd) intf_load.major = 0; intf_load.minor = 0;

• strncpy((char *)&intf_load.firmware_tag, firmware_tag,
  

•         GB_FIRMWARE_U_TAG_MAX_SIZE);
  

• strscpy((char *)&intf_load.firmware_tag, firmware_tag,
  

•         GB_FIRMWARE_U_TAG_MAX_SIZE + 1);
  
  ret = ioctl(fd, FW_MGMT_IOC_INTF_LOAD_AND_VALIDATE, &intf_load);
  if (ret < 0) {
  

@@ -101,8 +101,8 @@ static int update_backend_firmware(int fd) /* Get Backend Firmware Version */ printf("Getting Backend Firmware Version\n");

• strncpy((char *)&backend_fw_info.firmware_tag, firmware_tag,
  

•         GB_FIRMWARE_U_TAG_MAX_SIZE);
  

• strscpy((char *)&backend_fw_info.firmware_tag, firmware_tag,
  

•         GB_FIRMWARE_U_TAG_MAX_SIZE + 1);
  
  

retry_fw_version: ret = ioctl(fd, FW_MGMT_IOC_GET_BACKEND_FW, &backend_fw_info); @@ -129,8 +129,8 @@ static int update_backend_firmware(int fd) /* Try Backend Firmware Update over Unipro */ printf("Updating Backend Firmware\n");

• strncpy((char *)&backend_update.firmware_tag, firmware_tag,
  

•         GB_FIRMWARE_U_TAG_MAX_SIZE);
  

• strscpy((char *)&backend_update.firmware_tag, firmware_tag,
  

•         GB_FIRMWARE_U_TAG_MAX_SIZE + 1);
  
  

retry_fw_update: backend_update.status = 0; diff --git a/drivers/staging/greybus/greybus_firmware.h b/drivers/staging/greybus/greybus_firmware.h index b6042a82ada4..ad5b2c8a6461 100644 --- a/drivers/staging/greybus/greybus_firmware.h +++ b/drivers/staging/greybus/greybus_firmware.h @@ -38,20 +38,20 @@

/* IOCTL support */ struct fw_mgmt_ioc_get_intf_version {

• __u8 firmware_tag[GB_FIRMWARE_U_TAG_MAX_SIZE];
  

• __u8 firmware_tag[GB_FIRMWARE_U_TAG_MAX_SIZE + 1];
  __u16 major;
  __u16 minor;
  

} __packed;

struct fw_mgmt_ioc_get_backend_version {

• __u8 firmware_tag[GB_FIRMWARE_U_TAG_MAX_SIZE];
  

• __u8 firmware_tag[GB_FIRMWARE_U_TAG_MAX_SIZE + 1];
  __u16 major;
  __u16 minor;
  __u8 status;
  

} __packed;

struct fw_mgmt_ioc_intf_load_and_validate {

• __u8 firmware_tag[GB_FIRMWARE_U_TAG_MAX_SIZE];
  

• __u8 firmware_tag[GB_FIRMWARE_U_TAG_MAX_SIZE + 1];
  __u8 load_method;
  __u8 status;
  __u16 major;
  

@@ -59,7 +59,7 @@ struct fw_mgmt_ioc_intf_load_and_validate { } __packed;

struct fw_mgmt_ioc_backend_fw_update {

• __u8 firmware_tag[GB_FIRMWARE_U_TAG_MAX_SIZE];
  

• __u8 firmware_tag[GB_FIRMWARE_U_TAG_MAX_SIZE + 1];
  __u8 status;
  

} __packed;

You are changing the size of a userspace structure here, are you SURE this is allowed?

How was this tested?

thanks,

greg k-h

Hi,

You're absolutely right — changing the size of a userspace-visible structure like this is not allowed and I apologize for the oversight.

I did compile and boot the kernel with the patch applied, but I now realize that I should have also tested it against the actual userspace tooling to validate ABI compatibility — which I didn’t do. That was a miss on my part.

Thanks for the review and the guidance. I’ll fix the patch to preserve structure sizes and ensure safe null termination without breaking the ABI — likely by using strscpy() with size - 1 and setting the last byte explicitly if needed.

Apologies for the oversight.

Regards Pranav Tyagi