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sys/net/dhcpv6: reject truncated option headers - #23018
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miri64 merged 1 commit intoOct 29, 2026
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LGTM, just some minor clean-up request.
| for (dhcpv6_opt_t *opt = (dhcpv6_opt_t *)(&rep[sizeof(dhcpv6_msg_t)]); | ||
| len > 0; len -= _opt_len(opt), opt = _opt_next(opt)) { | ||
| if (len < sizeof(dhcpv6_opt_t)) { | ||
| DEBUG("DHCPv6 client: REPLY options truncated\n"); |
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The debug statement in the if branch below says "ADVERTISE". Could you maybe piggy-back a fix for that?
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oop, i can do a followup maybe?
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Short round of confusion I had, that others might have later: While the length field of the option header does not include the header itself, the result of _opt_len(opt) (which is used here) does.
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Backport provided in #23034 |
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Contribution description
The DHCPv6 option walker reads a four byte option header without checking that four bytes remain. A message with one to three trailing bytes after its last complete option makes the parser read past the end of the message.
The real recv_buf is 256 bytes and is followed by best_adv, so the read lands in valid static memory on normal builds. It reads one or two bytes only, and the values are used for parsing, never sent back to the attacker. There is no write, no code execution, and no reliable crash.
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