Should subprocNewProc() respect PATH?

[rragliamzanov]

I prepared /chroot/ with selected binaries in /chroot/bin/

When I run nsjail --chroot /chroot/ -E PATH=/bin date I got error:

[I][2021-04-21T14:49:04+0000] Executing 'date' for '[STANDALONE MODE]'
[D][2021-04-21T14:49:04+0000][1] void subproc::subprocNewProc(nsjconf_t*, int, int, int, int, int)():184  Arg: 'date'
[E][2021-04-21T14:49:04+0000][1] void subproc::subprocNewProc(nsjconf_t*, int, int, int, int, int)():205 execve('date') failed: No such file or directory
[F][2021-04-21T14:49:04+0000][1] bool subproc::runChild(nsjconf_t*, int, int, int, int)():448 Launching child process failed
[W][2021-04-21T14:49:04+0000][12] bool subproc::runChild(nsjconf_t*, int, int, int, int)():478 Received error message from the child process before it has been executed
[E][2021-04-21T14:49:04+0000][12] int nsjail::standaloneMode(nsjconf_t*)():256 Couldn't launch the child process
[D][2021-04-21T14:49:04+0000][12] int main(int, char**)():343 Returning with 255

Code of the function looks like it sets environment variables with putenv, but execv is called, which doesn't respect PATH when calling binaries.

[robertswiecki]

nsjail doesn't use PATH when executing commands, please try with /bin/date

[rragliamzanov]

It works will full path to the binary, but I have binaries in different directories and I need to call them by name only for this task.

nsjail doesn't use PATH when executing commands

There is a security reason for this or it is just unemplemented?

[fluxchief]

As far as I know only(?) shells use $PATH to execute files without full path for convenience reasons - you would not want to enter the full path on your shell the whole time.

Considering that nsjail is not a shell, I think it should not care about $PATH. Maybe you want to run a shell first and execute your command within that shell instead?

nsjail --chroot /chroot/ -E PATH=/bin /bin/sh -c 'date; id; echo Hi'

[robertswiecki]

Yup, we want to be specific when creating processes from binaries, as this might affect security (executing something that shouldn't be launched, because there are copies lying around in e.g. /usr/local)

There's also execv() (as opposed to execve() or fexecve()) which uses PATH, and this could be used here, but this should be only used with shells or with system() from processes - in situations where such search heuristics will not cause unwanted side-effects.

As @fluxchief mentioned, feel free to run your commands via /bin/sh -c - just you need -- before /bin/sh because some getopt() magic, so

nsjail --chroot / -E PATH=/bin:/usr/bin -- /bin/sh -c 'date; id; echo Hi'

[rragliamzanov]

Patching execv() call to execvp() has worked but with having possible security leak in mind.

Thanks for option with runnning shell.