icmp: Fixed replies to broadcasts. #6262
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xiaoxiang781216
approved these changes
May 13, 2022
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For future reference, this change was discussed in the NuttX mail list thread "ICMP responses on UDP broadcasts" started 10 May 2022, archived at https://lists.apache.org/thread/qly6hbt63bxocdorc2kk173nys1vgkvt and other places. |
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Summary
ICMP must not reply to broadcasts.
Currently, it is improperly checking whether the destination is a broadcast, by a pure equality check with INADDR_BROADCAST.
The broadcast address, as defined by the subnet mask, is not checked. This results in ICMP replying to broadcasts that it shouldn't.
The fix also takes into account the subnet mast, and checks against the calculated broadcast address, ensuring that only valid responses are sent.
Impact
There are no more ICMP responses to broadcasts.
Testing
Tested on a custom target, based on the STM32F427, using the LAN8720A.
Traffic was examined with Wireshark, with and without the fix, validating the fix.