Change what +RTS options are available by default
Ticket #3910 originally pointed out that the RTS options are a potential security problem. For example the -t -s or -S flags can be used to overwrite files. This would be bad in the context of CGI scripts or setuid binaries. So we introduced a system where +RTS processing is more or less disabled unless you pass the -rtsopts flag at link time. This scheme is safe enough but it also really annoies users. They have to use -rtsopts in many circumstances: with -threaded to use -N, with -eventlog to use -l, with -prof to use any of the profiling flags. Many users just set -rtsopts globally or in project .cabal files. Apart from annoying users it reduces security because it means that deployed binaries will have all RTS options enabled rather than just profiling ones. This patch relaxes the set of RTS options that are available in the default -rtsopts=some case. For "deployment" ways like vanilla and -threaded we remain quite conservative. Only --info -? --help are allowed for vanilla. For -threaded, -N and -N<x> are allowed with a check that x <= num cpus. For "developer" ways like -debug, -eventlog, -prof, we allow all the options that are special to that way. Some of these allow writing files, but the file written is not directly under the control of the attacker. For the setuid case (where the attacker would have control over binary name, current dir, local symlinks etc) we check if the process is running setuid/setgid and refuse all RTS option processing. Users would need to use -rtsopts=all in this case. We are making the assumption that developers will not deploy binaries built in the -debug, -eventlog, -prof ways. And even if they do, the damage should be limited to DOS, information disclosure and writing files like <progname>.eventlog, not arbitrary files.