Add restricted evaluation mode

If ‘--option restrict-eval true’ is given, the evaluator will throw an
exception if an attempt is made to access any file outside of the Nix
search path. This is primarily intended for Hydra, where we don't want
people doing ‘builtins.readFile ~/.ssh/id_dsa’ or stuff like that.

1 files changed, 21 insertions, 7 deletions

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index a4efd397ec7a..a4363c678a16 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -80,6 +80,8 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
             % path % e.path % pos);
     }
 
+    path = state.checkSourcePath(path);
+
     if (isStorePath(path) && store->isValidPath(path) && isDerivation(path)) {
         Derivation drv = readDerivation(path);
         Value & w = *state.allocValue();
@@ -133,7 +135,7 @@ static void prim_scopedImport(EvalState & state, const Pos & pos, Value * * args
 /* !!! Should we pass the Pos or the file name too? */
 extern "C" typedef void (*ValueInitializer)(EvalState & state, Value & v);
 
-/* Load a ValueInitializer from a dso and return whatever it initializes */
+/* Load a ValueInitializer from a DSO and return whatever it initializes */
 static void prim_importNative(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
@@ -146,6 +148,8 @@ static void prim_importNative(EvalState & state, const Pos & pos, Value * * args
             % path % e.path % pos);
     }
 
+    path = state.checkSourcePath(path);
+
     string sym = state.forceStringNoCtx(*args[1], pos);
 
     void *handle = dlopen(path.c_str(), RTLD_LAZY | RTLD_LOCAL);
@@ -380,7 +384,7 @@ static void prim_tryEval(EvalState & state, const Pos & pos, Value * * args, Val
 static void prim_getEnv(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     string name = state.forceStringNoCtx(*args[0], pos);
-    mkString(v, getEnv(name));
+    mkString(v, state.restricted ? "" : getEnv(name));
 }
 
 
@@ -680,7 +684,7 @@ static void prim_toPath(EvalState & state, const Pos & pos, Value * * args, Valu
 static void prim_storePath(EvalState & state, const Pos & pos, Value * * args, Value & v)
 {
     PathSet context;
-    Path path = state.coerceToPath(pos, *args[0], context);
+    Path path = state.checkSourcePath(state.coerceToPath(pos, *args[0], context));
     /* Resolve symlinks in ‘path’, unless ‘path’ itself is a symlink
        directly in the store.  The latter condition is necessary so
        e.g. nix-push does the right thing. */
@@ -701,7 +705,15 @@ static void prim_pathExists(EvalState & state, const Pos & pos, Value * * args,
     Path path = state.coerceToPath(pos, *args[0], context);
     if (!context.empty())
         throw EvalError(format("string ‘%1%’ cannot refer to other paths, at %2%") % path % pos);
-    mkBool(v, pathExists(path));
+    try {
+        mkBool(v, pathExists(state.checkSourcePath(path)));
+    } catch (SysError & e) {
+        /* Don't give away info from errors while canonicalising
+           ‘path’ in restricted mode. */
+        mkBool(v, false);
+    } catch (RestrictedPathError & e) {
+        mkBool(v, false);
+    }
 }
 
 
@@ -736,7 +748,7 @@ static void prim_readFile(EvalState & state, const Pos & pos, Value * * args, Va
         throw EvalError(format("cannot read ‘%1%’, since path ‘%2%’ is not valid, at %3%")
             % path % e.path % pos);
     }
-    mkString(v, readFile(path).c_str());
+    mkString(v, readFile(state.checkSourcePath(path)).c_str());
 }
 
 
@@ -763,7 +775,7 @@ static void prim_findFile(EvalState & state, const Pos & pos, Value * * args, Va
             throw EvalError(format("attribute ‘path’ missing, at %1%") % pos);
         string path = state.coerceToPath(pos, *i->value, context);
 
-        searchPath.push_back(std::pair<string, Path>(prefix, path));
+        searchPath.push_back(std::pair<string, Path>(prefix, state.checkSourcePath(path)));
     }
 
     string path = state.forceStringNoCtx(*args[1], pos);
@@ -790,7 +802,7 @@ static void prim_readDir(EvalState & state, const Pos & pos, Value * * args, Val
             % path % e.path % pos);
     }
 
-    DirEntries entries = readDirectory(path);
+    DirEntries entries = readDirectory(state.checkSourcePath(path));
     state.mkAttrs(v, entries.size());
 
     for (auto & ent : entries) {
@@ -927,6 +939,8 @@ static void prim_filterSource(EvalState & state, const Pos & pos, Value * * args
 
     FilterFromExpr filter(state, *args[0]);
 
+    path = state.checkSourcePath(path);
+
     Path dstPath = settings.readOnlyMode
         ? computeStorePathForPath(path, true, htSHA256, filter).first
         : store->addToStore(path, true, htSHA256, filter, state.repair);