fix(gps): bound GSV satellite records

[timothyanderson096-ocdealcheck]

Summary

Harden the standard NMEA and Ashtech GSV parsers against receiver-controlled satellite counts and page metadata.

A checksummed sentence such as $GPGSV,1,1,200*4B previously drove the parsers past their four-record local sat arrays. Large page numbers could also address beyond the satellite_info_s arrays. The same pattern existed in both parsers.

This change:

• parses only complete satellite records actually present in the sentence;
• caps each GSV page at four records;
• rejects negative or internally impossible page metadata;
• bounds destination indices to SAT_INFO_MAX_SATELLITES; and
• clamps the published NMEA satellite count.

Fixes PX4/PX4-Autopilot#28348.

Verification

• Reproduced current PX4 SITL under AddressSanitizer using a pseudo-serial NMEA GPS with GPS_SAT_INFO=1.
• Baseline: stack-buffer-overflow in GPSDriverNMEA::handleMessage() at nmea.cpp:748; PX4 aborted.
• Independently reproduced the same class in GPSDriverAshtech::handleMessage() at ashtech.cpp:570.
• Patched ASan SITL survived the original malformed payload in both protocol paths.
• Valid four-satellite GSV preserved IDs 1,2,3,4 and SNR values 30,31,32,33.
• Page 11/11 with 44 satellites did not write beyond the 40-slot telemetry arrays.
• make px4_sitl_default (RelWithDebInfo): pass.
• make px4_sitl_default PX4_CMAKE_BUILD_TYPE=AddressSanitizer: pass.
• make check_format: pass.
• GPSDrivers CTest: 1/1 pass.

AI assistance and independent validation

OpenAI Codex assisted with this implementation. GDN operated as a separate, coding-platform-independent validation layer above the coding system: it reproduced the fault in both protocol paths and assessed the patch through sanitizer, build, formatting, and protocol-behavior evidence. The same GDN process can validate work produced using any AI coding platform.

Assisted-by: OpenAI:Codex

[dakejahl]

Tested on hardware?

[timothyanderson096-ocdealcheck]

Not on physical hardware—I don’t currently have a compatible receiver available. Verification was performed in PX4 SITL using a pseudo-serial NMEA GPS under AddressSanitizer. The malformed payload reproduced the baseline overflows in both the NMEA and Ashtech paths; the patched builds survived the same cases while preserving valid GSV behaviour.

The normal and AddressSanitizer SITL builds, formatting check, and GPSDrivers CTest all passed.