linux: Fix sockopt copyout

[chuck]

Summary

The Linux getsockopt did not check the size of the provided buffer when
copying out the value, leading to buffer overflows (e.g., for TCP_INFO).

Fix is to use the smaller of the option value size and the provided
buffer.

[kib]

sys/compat/linux/linux_socket.c

2199

Is it right to use FreeBSD-native type for socklen? Do we need e.g. linux_socklen_t, if we do not have it already?

[chuck]

sys/compat/linux/linux_socket.c

2199

There is a l_socklen_t in sys/amd64/linux/linux.h, but it is defined as an l_ulong. Since linux_getsockopt_args defines optlen as l_uintptr_t, perhaps this should be l_uint?

[kib]

sys/compat/linux/linux_socket.c

2199

But why l_uint? It should be l_socklen_t, no?

[markj]

sys/compat/linux/linux_socket.c

2199

In the Linux sources the type is int *. I don't know why our emulator uses l_uintptr_t, it looks incorrect. Probably that should be fixed.