net: wwan: mhi_wwan_mbim: Avoid -Wflex-array-member-not-at-end warning

Use DEFINE_RAW_FLEX() to avoid a -Wflex-array-member-not-at-end warning.

Remove fixed-size array struct usb_cdc_ncm_dpe16 dpe16[2]; from struct mbim_tx_hdr, so that flex-array member struct mbim_tx_hdr::ndp16.dpe16[] ends last in this structure.

Compensate for this by using the DEFINE_RAW_FLEX() helper to declare the on-stack struct instance that contains struct usb_cdc_ncm_ndp16 as a member. Adjust the rest of the code, accordingly.

So, with these changes fix the following warning:

drivers/net/wwan/mhi_wwan_mbim.c:81:34: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
Changes in v2:
- Add code comment to prevent people from adding new members after flex struct member struct usb_cdc_ncm_ndp16 ndp16;

v1:
- Link: https://lore.kernel.org/linux-hardening/aSUubvYfGJ-BIeDq@kspp/

 drivers/net/wwan/mhi_wwan_mbim.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

drivers/net/wwan/mhi_wwan_mbim.c +8 -9

index c814fbd756a1..313dc5207c93 100644
@@ -78,8 +78,9 @@ struct mhi_mbim_context {
 
 struct mbim_tx_hdr {
        struct usb_cdc_ncm_nth16 nth16;
+
+       /* Must be last as it ends in a flexible-array member. */
        struct usb_cdc_ncm_ndp16 ndp16;
-       struct usb_cdc_ncm_dpe16 dpe16[2];
 } __packed;
 
 static struct mhi_mbim_link *mhi_mbim_get_link_rcu(struct mhi_mbim_context *mbim,

@@ -107,20 +108,20 @@ static int mhi_mbim_get_link_mux_id(struct mhi_controller *cntrl)
 static struct sk_buff *mbim_tx_fixup(struct sk_buff *skb, unsigned int session,
                                     u16 tx_seq)
 {
+       DEFINE_RAW_FLEX(struct mbim_tx_hdr, mbim_hdr, ndp16.dpe16, 2);
        unsigned int dgram_size = skb->len;
        struct usb_cdc_ncm_nth16 *nth16;
        struct usb_cdc_ncm_ndp16 *ndp16;
-       struct mbim_tx_hdr *mbim_hdr;
 
        /* Only one NDP is sent, containing the IP packet (no aggregation) */
 
        /* Ensure we have enough headroom for crafting MBIM header */
-       if (skb_cow_head(skb, sizeof(struct mbim_tx_hdr))) {
+       if (skb_cow_head(skb, __struct_size(mbim_hdr))) {
                dev_kfree_skb_any(skb);
                return NULL;
        }
 
-       mbim_hdr = skb_push(skb, sizeof(struct mbim_tx_hdr));
+       mbim_hdr = skb_push(skb, __struct_size(mbim_hdr));
 
        /* Fill NTB header */
        nth16 = &mbim_hdr->nth16;

@@ -133,12 +134,11 @@ static struct sk_buff *mbim_tx_fixup(struct sk_buff *skb, unsigned int session,
        /* Fill the unique NDP */
        ndp16 = &mbim_hdr->ndp16;
        ndp16->dwSignature = cpu_to_le32(USB_CDC_MBIM_NDP16_IPS_SIGN | (session << 24));
-       ndp16->wLength = cpu_to_le16(sizeof(struct usb_cdc_ncm_ndp16)
-                                       + sizeof(struct usb_cdc_ncm_dpe16) * 2);
+       ndp16->wLength = cpu_to_le16(struct_size(ndp16, dpe16, 2));
        ndp16->wNextNdpIndex = 0;
 
        /* Datagram follows the mbim header */
-       ndp16->dpe16[0].wDatagramIndex = cpu_to_le16(sizeof(struct mbim_tx_hdr));
+       ndp16->dpe16[0].wDatagramIndex = cpu_to_le16(__struct_size(mbim_hdr));
        ndp16->dpe16[0].wDatagramLength = cpu_to_le16(dgram_size);
 
        /* null termination */

@@ -584,7 +584,7 @@ static void mhi_mbim_setup(struct net_device *ndev)
 {
        ndev->header_ops = NULL;  /* No header */
        ndev->type = ARPHRD_RAWIP;
-       ndev->needed_headroom = sizeof(struct mbim_tx_hdr);
+       ndev->needed_headroom = struct_size_t(struct mbim_tx_hdr, ndp16.dpe16, 2);
        ndev->hard_header_len = 0;
        ndev->addr_len = 0;
        ndev->flags = IFF_POINTOPOINT | IFF_NOARP;
--

2.43.0

Quoted 13 lines · Gustavo A. R. Silva

Use DEFINE_RAW_FLEX() to avoid a -Wflex-array-member-not-at-end warning.

Remove fixed-size array struct usb_cdc_ncm_dpe16 dpe16[2]; from struct mbim_tx_hdr, so that flex-array member struct mbim_tx_hdr::ndp16.dpe16[] ends last in this structure.

Compensate for this by using the DEFINE_RAW_FLEX() helper to declare the on-stack struct instance that contains struct usb_cdc_ncm_ndp16 as a member. Adjust the rest of the code, accordingly.

So, with these changes fix the following warning:

Quoted 3 lines

drivers/net/wwan/mhi_wwan_mbim.c:81:34: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by Gustavo A. R. Silva <[email protected]>

I just noticed there’s a V2, so:

Reviewed-by Loic Poulain <[email protected]>