setuid-wrapper activationScript is not atomic #18124
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shlevy
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Aug 31, 2016
This makes the replacement of the old wapper dir with the new one atomic if the kernel and FS support RENAME_EXCHANGE, and falls back to at least ensuring the old wrapper dir remains on the FS if interrupted during the (now smaller) inconsistent window. Fixes NixOS#18124
shlevy
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Aug 31, 2016
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@edolstra @shlevy so this was failing because it's ready a tmpfs upon install: So, if we want My proposal would be to make Thoughts? |
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I think it would be better to just not have /var/setuid-wrappers be a tmpfs since we're symlinking to a tmpfs anyway. |
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@domenkozar Well, we can just change nixos-install not to create that tmpfs, right? Not sure why it's doing that anyway... |
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I'll have a PR ready soon, fixing a bug atm. |
domenkozar
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Sep 1, 2016
Before this commit updating /var/setuid-wrappers/ folder introduced a small window where NixOS activation scripts could be terminated and resulted into empty /var/setuid-wrappers/ folder. That's very unfortunate because one might lose sudo binary. Instead we use two atomic operations mv and ln (as described in https://axialcorps.com/2013/07/03/atomically-replacing-files-and-directories/) to achieve atomicity. Since /var/setuid-wrappers is not a directory anymore, tmpfs mountpoints were removed in installation scripts and in boot process. Tested: - upgrade /var/setuid-wrappers/ from folder to a symlink - make sure /run/setuid-wrappers-dirs/ legacy symlink is really deleted
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It's currently possible to cancel
nixos-rebuildbetween deletion of previous setuid wrappers and population of new ones. And yes, I've been able to lock myself out of machine (almost, if I didn't have root ssh key).Current implementation: https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/security/setuid-wrappers.nix#L118-L120
Proposed implementation (see at the bottom of blog post): https://axialcorps.com/2013/07/03/atomically-replacing-files-and-directories/
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