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Add compile-time sanity check on multi_send_data_direct length

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JoeNotCharles reported
<1f1903a3b9>
an overflow in `net_udp_send_mdata_direct`.  This overflow is impossible
as currently written, because it can occur only if
`multi_send_data_direct` passes an oversized buffer to
`net_udp_send_mdata_direct`, and no messages are large enough to trigger
this.  JoeNotCharles proposed adding a runtime check to abort the
program if this happens.  Instead, this commit adds a compile-time check
to detect use of an excessively large input buffer.
This commit is contained in:
Kp 2023-01-14 19:05:37 +00:00
parent 6cbfc2fd55
commit b6ce89eb54
1 changed files with 18 additions and 0 deletions
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18
similar/main/multi.cpp
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@ -1061,6 +1061,24 @@ window_event_result multi_do_frame()
namespace {
template <multiplayer_command_t C>
#ifndef __clang__
/* udp::dispatch_table::send_data_direct copies `buf` into a buffer sized from
* `UDP_mdata_info`. Require that no overflow will occur.
*
* Guard this with `#ifndef __clang__` because clang-14 rejects this constraint
* with the error:
similar/main/multi.cpp:1068:22: note: because '(std::size(buf) + 6 <= sizeof(UDP_mdata_info))' would be invalid: constraint variable 'buf' cannot be used in an evaluated context
* gcc accepts this requires() constraint and enforces it as intended. Raising
* the `6` to `6000` correctly provokes a rejection.
*/
requires(
requires(multi_command<C> buf) {
requires(std::size(buf) + 6 <= sizeof(UDP_mdata_info));
}
)
#endif
static inline void multi_send_data_direct(const multi_command<C> &buf, const playernum_t pnum, const int priority)
{
multi::dispatch->send_data_direct(buf, pnum, priority);