fuzz: rework df_exec_cmd_check()

[mrc0mmand]

Explicitly use fork() & execl() to avoid the file descriptor
shenanigans, and move & rename the function to util.[ch].

Also, when at it, add a unit test for the function as well.

[evverx]

@mrc0mmand could you move the first commit (with g_assert) to a separate PR? I think it should be good to go.

[mrc0mmand]

@mrc0mmand could you move the first commit (with g_assert) to a separate PR? I think it should be good to go.

Sure thing, done in #121.

[mrc0mmand]

@evverx I tweaked the logging stuff a bit, so we can differentiate between multiple logging handles - in our case it only general and command (so far) - and made --debug accept an optional argument, so now we can do --debug or --debug=general for the expected/current behavior, --debug=command to show only output from the --command, and --debug=all to show everything. Hopefully it makes sense.

[evverx]

now we can do --debug or --debug=general for the expected/current behavior, --debug=command to show only output from the --command

I'm kind of on the fence about this. On the one hand it should make it possible to extend that part easily but on the other hand as a user I'd prefer to pass something like -e '/some/weird/script' --keep-command-output' and be done with it.

[mrc0mmand]

now we can do --debug or --debug=general for the expected/current behavior, --debug=command to show only output from the --command

I'm kind of on the fence about this. On the one hand it should make it possible to extend that part easily but on the other hand as a user I'd prefer to pass something like -e '/some/weird/script' --keep-command-output' and be done with it.

I don't really have a preference here, so I can definitely leave the --debug option as is and just add a new one :-)

[evverx]

Just to clarify, I'm just used to tools where I have to flip a switch like -Q in honggfuzz or AFL_DEBUG_CHILD in afl-fuzz to start capturing the output of various binaries so whatever I'm saying here is subjective and can be ignored :-)

[evverx]

I can definitely leave the --debug option as is and just add a new one :-)

I think I'd go with this. If at some point it causes any issues in terms of extending the logger it will be on me :-)

[evverx]

@mrc0mmand one last thing. I wonder what was wrong with system? It seems to me that it would be shorter than fork/execl at least.

[evverx]

I think I should have read the commit message carefully. fork followed up by execl lets dfuzzer avoid saving/restoring its stdin/stdout/stderr with dup/dup2. LGTM. I'll go ahead and merge it. Thanks!