can: j1939: j1939_tp_tx_dat_new(): fix out-of-bounds memory access

In the Linux kernel, the following vulnerability has been resolved:

can: j1939: j1939_tp_tx_dat_new(): fix out-of-bounds memory access

In the j1939_tp_tx_dat_new() function, an out-of-bounds memory access

could occur during the memcpy() operation if the size of skb->cb is

larger than the size of struct j1939_sk_buff_cb. This is because the

memcpy() operation uses the size of skb->cb, leading to a read beyond

the struct j1939_sk_buff_cb.

Updated the memcpy() operation to use the size of struct

j1939_sk_buff_cb instead of the size of skb->cb. This ensures that the

memcpy() operation only reads the memory within the bounds of struct

j1939_sk_buff_cb, preventing out-of-bounds memory access.

Additionally, add a BUILD_BUG_ON() to check that the size of skb->cb

is greater than or equal to the size of struct j1939_sk_buff_cb. This

ensures that the skb->cb buffer is large enough to hold the

j1939_sk_buff_cb structure.

[mkl: rephrase commit message]