if_ovpn.c: fix use of uninitialized variable

[arichardson]

Summary

In case we use OVPN_CIPHER_ALG_NONE, the memcpy will attempt to copy 0
bytes from an uninitialized pointer. While the memcpy() implementation
will treat this as a no-op and not actually dereferece the undefined
variable it is still undefined behaviour to the compiler and should be
fixed. Found by building with clang HEAD

[jrtc27]

sys/net/if_ovpn.c

908

I don't understand this code. Where does kdir->key come from? Isn't it NULL from the malloc(M_ZERO) above? How is this not a NULL dereference is cipher *isn't* OVPN_CIPHER_ALG_NONE?

[arichardson]

sys/net/if_ovpn.c

908

I didn't even notice this! No idea how this is supposed to work?

[arichardson]

sys/net/if_ovpn.c

908

Aha it's an array inside a struct so it's decaying here.