• Duncan Coutts's avatar
    Change what +RTS options are available by default · 8c7ad0bd
    Duncan Coutts authored
    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
    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.
RtsFlags.c 53.8 KB