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gh-100163: allow re-assuming root privileges on subprocess invocations #134400
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This is a preparatory refactoring which should have no semantic effect in itself but will hopefully make the real changes coming in subsequent patches easier to review.
Setting the saved user/group-ID allows the code to re-assume privileges after dropping them.
When dropping privileges we need to set the new effective UID last, so we have permission to change the gid/groups. When re-assuming root privileges we need to do the opposite: set the UID first so we then have permission to change gid/groups.
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status: I'm marking this as a Draft as we're deciding (see issue) on if this is the right approach. manual testing likely required due to privs. required. |
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The
subprocess.Popenclass takes user/group/extra groups parameters which allow invocations to run as a different user. When dropping privileges (i.e. the main program is running as root but wants to run a subprocess as an unprivileged user) this works fine. However, it fails if a program wants to drop privileges and re-assume them to run a subprocess.To allow this there are a couple of changes required:
setresuid/setresgidinstead ofsetreuid/setregidso the saved user/group identity can be re-assumed after it has been dropped.Naturally we need to continue to set the user identity last when going from root to an unprivileged user, so the order of calls needs to be determined dynamically based on whether we are switching to or from root.