strncpy() is deprecated for use on NUL-terminated destination strings [0] and as such we should prefer more robust and less ambiguous string interfaces. The CAPI (part II) [1] states that the manufacturer id should be a "zero-terminated ASCII string" and should "always [be] zero-terminated." Much the same for the serial number: "The serial number, a seven-digit number coded as a zero-terminated ASCII string". Along with this, its clear the original author intended for these buffers to be NUL-padded as well. To meet the specification as well as properly NUL-pad, use strscpy_pad(). In doing this, an opportunity to simplify this code is also present. Remove the min_t() and combine the length check into the main if. Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [0] Link: https://capi.org/downloads.html [1] Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html Link: https://github.com/KSPP/linux/issues/90 Cc: linux-hardening@xxxxxxxxxxxxxxx Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx> --- Note: build-tested only. For future travelers: skb->data + CAPI_MSG_BASELN + 14 is a byte that specifies the length of the message to follow, and of course "... + 15" is the offset of the message itself. Due to this, we cannot use the more appropriate memtostr_pad() because we don't know all the sizes at compile time. --- net/bluetooth/cmtp/capi.c | 32 ++++++++------------------------ 1 file changed, 8 insertions(+), 24 deletions(-) diff --git a/net/bluetooth/cmtp/capi.c b/net/bluetooth/cmtp/capi.c index f3bedc3b613a..884703fda979 100644 --- a/net/bluetooth/cmtp/capi.c +++ b/net/bluetooth/cmtp/capi.c @@ -248,18 +248,10 @@ static void cmtp_recv_interopmsg(struct cmtp_session *session, struct sk_buff *s break; case CAPI_FUNCTION_GET_MANUFACTURER: - if (skb->len < CAPI_MSG_BASELEN + 15) - break; - - if (!info && ctrl) { - int len = min_t(uint, CAPI_MANUFACTURER_LEN, - skb->data[CAPI_MSG_BASELEN + 14]); - - memset(ctrl->manu, 0, CAPI_MANUFACTURER_LEN); - strncpy(ctrl->manu, - skb->data + CAPI_MSG_BASELEN + 15, len); - } - + if (!info && ctrl && skb->len > CAPI_MSG_BASELEN + 14) + strscpy_pad(ctrl->manu, + skb->data + CAPI_MSG_BASELEN + 15, + skb->data[CAPI_MSG_BASELEN + 14]); break; case CAPI_FUNCTION_GET_VERSION: @@ -276,18 +268,10 @@ static void cmtp_recv_interopmsg(struct cmtp_session *session, struct sk_buff *s break; case CAPI_FUNCTION_GET_SERIAL_NUMBER: - if (skb->len < CAPI_MSG_BASELEN + 17) - break; - - if (!info && ctrl) { - int len = min_t(uint, CAPI_SERIAL_LEN, - skb->data[CAPI_MSG_BASELEN + 16]); - - memset(ctrl->serial, 0, CAPI_SERIAL_LEN); - strncpy(ctrl->serial, - skb->data + CAPI_MSG_BASELEN + 17, len); - } - + if (!info && ctrl && skb->len > CAPI_MSG_BASELEN + 16) + strscpy_pad(ctrl->serial, + skb->data + CAPI_MSG_BASELEN + 17, + skb->data[CAPI_MSG_BASELEN + 16]); break; } --- base-commit: 521b1e7f4cf0b05a47995b103596978224b380a8 change-id: 20240905-strncpy-net-bluetooth-cmtp-capi-c-85b23d830279 Best regards, -- Justin Stitt <justinstitt@xxxxxxxxxx>
