AZL-90156

Socket versions before 2.041 for Perl have an out-of-bounds heap read.

In Socket.xs, packipmreqsource() checks the length of its source argument before the argument is read, so the check tests the byte length carried over from the preceding multiaddr argument instead. Both addresses occupy a 4-byte field, so a valid multiaddr lets a source of any length pass the check, and the source is then copied into the 4-byte imrsourceaddr field with a fixed-size copy. A source shorter than 4 bytes is not rejected, and the copy reads up to 3 bytes past the end of its buffer.

Calling packipmreq_source() with a source value shorter than 4 bytes copies adjacent heap memory into the returned packed structure.