Merge pull request #5875 from hercules-ci/fix-large-drv-field-stack-overflow

Fix segfault or stack overflow caused by large derivation fields

src/libstore/derivations.cc

@@ -4,6 +4,7 @@
 #include "util.hh"
 #include "worker-protocol.hh"
 #include "fs-accessor.hh"
+#include <boost/container/small_vector.hpp>
 
 namespace nix {
 
@@ -272,7 +273,9 @@ Derivation parseDerivation(const Store & store, std::string && s, std::string_vi
 
 static void printString(string & res, std::string_view s)
 {
-    char buf[s.size() * 2 + 2];
+    boost::container::small_vector<char, 64 * 1024> buffer;
+    buffer.reserve(s.size() * 2 + 2);
+    char * buf = buffer.data();
     char * p = buf;
     *p++ = '"';
     for (auto c : s)

tests/big-derivation-attr.nix

@@ -0,0 +1,13 @@
+let
+  sixteenBytes = "0123456789abcdef";
+  times16 = s: builtins.concatStringsSep "" [s s s s s s s s s s s s s s s s];
+  exp = n: x: if n == 1 then x else times16 (exp (n - 1) x);
+  sixteenMegabyte = exp 6 sixteenBytes;
+in
+assert builtins.stringLength sixteenMegabyte == 16777216;
+derivation {
+  name = "big-derivation-attr";
+  builder = "/x";
+  system = "y";
+  bigAttr = sixteenMegabyte;
+}

tests/simple.sh

@@ -25,3 +25,9 @@ if test "$outPath" != "/foo/lfy1s6ca46rm5r6w4gg9hc0axiakjcnm-dependencies.drv";
     echo "hashDerivationModulo appears broken, got $outPath"
     exit 1
 fi
+
+outPath="$(NIX_REMOTE=local?store=/foo\&real=$TEST_ROOT/real-store nix-instantiate --readonly-mode big-derivation-attr.nix)"
+if test "$outPath" != "/foo/xxiwa5zlaajv6xdjynf9yym9g319d6mn-big-derivation-attr.drv"; then
+    echo "big-derivation-attr.nix hash appears broken, got $outPath. Memory corruption in large drv attr?"
+    exit 1
+fi