pptp: reject control messages shorter than the header

PPTP_CTRL_SIZE() evaluates to 0 for unrecognised control types, so a
message declaring length 0 with such a type passed the length check,
reached process_packet() and was logged as unknown, after which
in_size -= 0 consumed nothing. The stale header stayed at the head of
the buffer and every later byte queued behind it, so the connection
could never make progress: it stalled until in_size reached
PPTP_CTRL_SIZE_MAX, at which point read() was called with a zero-length
buffer, returned 0 and was misreported as "disconnect by peer".

Require the declared length to cover the header, alongside the existing
upper bound.

0 files changed, 0 insertions, 0 deletions