bound capwap decap reads to caplen in dissectPacket - #10487
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The CAPWAP UDP tunnel branch in dissectPacket reads the header-length byte at packet[ip_offset + 1] before checking that byte is inside the captured data, then advances ip_offset by that value and compares the result against h->len. h->len is the on-wire frame size, not h->caplen, so on a snaplen-truncated capture (caplen < len) the header-length read and the later packet[ip_offset - 2] and inner IP reads run past the end of the packet buffer. A crafted CAPWAP-data UDP packet triggers it, and tunnel decoding is on by default.
Before, this branch trusted h->len for the bound while every sibling tunnel case (GRE, ERSPAN, GTP, L2TP, 6in4) bounds against h->caplen. After, the header-length byte is guarded against h->caplen first and the advanced offset is compared to h->caplen as well. The tradeoff is that a CAPWAP frame whose header was clipped by the snap length is now dropped instead of parsed from uncaptured bytes, which is how the other decoders already behave.