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Author SHA1 Message Date
Robert Hensing d038a67bd3 Fix segfault or stack overflow caused by large derivation fields
This removes a dynamic stack allocation, making the derivation
unparsing logic robust against overflows when large strings are
added to a derivation.
Overflow behavior depends on the platform and stack configuration.

For instance, x86_64-linux/glibc behaves as (somewhat) expected:

$ (ulimit -s 20000; nix-instantiate tests/lang/eval-okay-big-derivation-attr.nix)
error: stack overflow (possible infinite recursion)

$ (ulimit -s 40000; nix-instantiate tests/lang/eval-okay-big-derivation-attr.nix)
error: expression does not evaluate to a derivation (or a set or list of those)

However, on aarch64-darwin:

$ nix-instantiate big-attr.nix                                                                                                                                                                                                                                                       ~
zsh: segmentation fault  nix-instantiate big-attr.nix

This indicates a slight flaw in the single stack protection page
approach that is not encountered with normal stack frames.
2022-01-19 15:21:56 +01:00