findRoots(): Add 'censor' parameter

This is less brittle than filtering paths after the fact in
nix-daemon.

src/libstore/gc.cc

@@ -129,7 +129,7 @@ Path LocalFSStore::addPermRoot(const Path & _storePath,
        check if the root is in a directory in or linked from the
        gcroots directory. */
     if (settings.checkRootReachability) {
-        Roots roots = findRoots();
+        Roots roots = findRoots(false);
         if (roots[storePath].count(gcRoot) == 0)
             printError(
                 format(
@@ -197,7 +197,10 @@ void LocalStore::addTempRoot(const Path & path)
 }
 
 
-void LocalStore::findTempRoots(FDs & fds, Roots & tempRoots)
+static std::string censored = "{censored}";
+
+
+void LocalStore::findTempRoots(FDs & fds, Roots & tempRoots, bool censor)
 {
     /* Read the `temproots' directory for per-process temporary root
        files. */
@@ -248,7 +251,7 @@ void LocalStore::findTempRoots(FDs & fds, Roots & tempRoots)
             Path root(contents, pos, end - pos);
             debug("got temporary root '%s'", root);
             assertStorePath(root);
-            tempRoots[root].emplace(fmt("{temp:%d}", pid));
+            tempRoots[root].emplace(censor ? censored : fmt("{temp:%d}", pid));
             pos = end + 1;
         }
 
@@ -317,7 +320,7 @@ void LocalStore::findRoots(const Path & path, unsigned char type, Roots & roots)
 }
 
 
-void LocalStore::findRootsNoTemp(Roots & roots)
+void LocalStore::findRootsNoTemp(Roots & roots, bool censor)
 {
     /* Process direct roots in {gcroots,profiles}. */
     findRoots(stateDir + "/" + gcRootsDir, DT_UNKNOWN, roots);
@@ -327,17 +330,17 @@ void LocalStore::findRootsNoTemp(Roots & roots)
        NIX_ROOT_FINDER environment variable.  This is typically used
        to add running programs to the set of roots (to prevent them
        from being garbage collected). */
-    findRuntimeRoots(roots);
+    findRuntimeRoots(roots, censor);
 }
 
 
-Roots LocalStore::findRoots()
+Roots LocalStore::findRoots(bool censor)
 {
     Roots roots;
-    findRootsNoTemp(roots);
+    findRootsNoTemp(roots, censor);
 
     FDs fds;
-    findTempRoots(fds, roots);
+    findTempRoots(fds, roots, censor);
 
     return roots;
 }
@@ -381,7 +384,7 @@ static void readFileRoots(const char * path, Roots & roots)
     }
 }
 
-void LocalStore::findRuntimeRoots(Roots & roots)
+void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
 {
     Roots unchecked;
 
@@ -467,7 +470,10 @@ void LocalStore::findRuntimeRoots(Roots & roots)
             Path path = toStorePath(target);
             if (isStorePath(path) && isValidPath(path)) {
                 debug(format("got additional root '%1%'") % path);
-                roots[path].insert(links.begin(), links.end());
+                if (censor)
+                    roots[path].insert(censored);
+                else
+                    roots[path].insert(links.begin(), links.end());
             }
         }
     }
@@ -739,7 +745,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
     printError(format("finding garbage collector roots..."));
     Roots rootMap;
     if (!options.ignoreLiveness)
-       findRootsNoTemp(rootMap);
+        findRootsNoTemp(rootMap, true);
 
     for (auto & i : rootMap) state.roots.insert(i.first);
 
@@ -748,7 +754,7 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
        can be added to the set of temporary roots. */
     FDs fds;
     Roots tempRoots;
-    findTempRoots(fds, tempRoots);
+    findTempRoots(fds, tempRoots, true);
     for (auto & root : tempRoots)
         state.tempRoots.insert(root.first);
     state.roots.insert(state.tempRoots.begin(), state.tempRoots.end());

src/libstore/local-store.hh

@@ -180,11 +180,11 @@ private:
     typedef std::shared_ptr<AutoCloseFD> FDPtr;
     typedef list<FDPtr> FDs;
 
-    void findTempRoots(FDs & fds, Roots & roots);
+    void findTempRoots(FDs & fds, Roots & roots, bool censor);
 
 public:
 
-    Roots findRoots() override;
+    Roots findRoots(bool censor) override;
 
     void collectGarbage(const GCOptions & options, GCResults & results) override;
 
@@ -267,9 +267,9 @@ private:
 
     void findRoots(const Path & path, unsigned char type, Roots & roots);
 
-    void findRootsNoTemp(Roots & roots);
+    void findRootsNoTemp(Roots & roots, bool censor);
 
-    void findRuntimeRoots(Roots & roots);
+    void findRuntimeRoots(Roots & roots, bool censor);
 
     void removeUnusedLinks(const GCState & state);
 

src/libstore/remote-store.cc

@@ -596,7 +596,7 @@ void RemoteStore::syncWithGC()
 }
 
 
-Roots RemoteStore::findRoots()
+Roots RemoteStore::findRoots(bool censor)
 {
     auto conn(getConnection());
     conn->to << wopFindRoots;

src/libstore/remote-store.hh

@@ -82,7 +82,7 @@ public:
 
     void syncWithGC() override;
 
-    Roots findRoots() override;
+    Roots findRoots(bool censor) override;
 
     void collectGarbage(const GCOptions & options, GCResults & results) override;
 

src/libstore/store-api.hh

@@ -484,8 +484,10 @@ public:
 
     /* Find the roots of the garbage collector.  Each root is a pair
        (link, storepath) where `link' is the path of the symlink
-       outside of the Nix store that point to `storePath'.  */
-    virtual Roots findRoots()
+       outside of the Nix store that point to `storePath'. If
+       'censor' is true, privacy-sensitive information about roots
+       found in /proc is censored. */
+    virtual Roots findRoots(bool censor)
     { unsupported("findRoots"); }
 
     /* Perform a garbage collection. */

src/nix-daemon/nix-daemon.cc

@@ -475,40 +475,19 @@ static void performOp(TunnelLogger * logger, ref<Store> store,
 
     case wopFindRoots: {
         logger->startWork();
-        Roots roots = store->findRoots();
+        Roots roots = store->findRoots(true);
         logger->stopWork();
 
-        // Pre-compute roots length using same algo as below.
-        size_t total_length = 0;
-        bool hasMemoryLink;
-        for (auto & root : roots) {
-            hasMemoryLink = false;
-            for (auto & link : root.second) {
-                if (link.rfind("{memory:", 0) == 0) {
-                    if (hasMemoryLink) continue;
-                    ++total_length;
-                    hasMemoryLink = true;
-                } else {
-                    ++total_length;
-                }
-            }
-        }
+        size_t size = 0;
+        for (auto & i : roots)
+            size += i.second.size();
+
+        to << size;
+
+        for (auto & [target, links] : roots)
+            for (auto & link : links)
+                to << link << target;
 
-        to << total_length;
-        int n = 0;
-        for (auto & [target, links] : roots) {
-            bool hasMemoryLink = false;
-            for (auto & link : links) {
-                // Obfuscate 'memory' roots as they expose information about other users,
-                if (link.rfind("{memory:", 0) == 0) {
-                    if (hasMemoryLink) continue;
-                    to << fmt("{memory:%d}", n++) << target;
-                    hasMemoryLink = true;
-                } else {
-                    to << link << target;
-                }
-            }
-        }
         break;
     }
 

src/nix-store/nix-store.cc

@@ -427,7 +427,7 @@ static void opQuery(Strings opFlags, Strings opArgs)
                     maybeUseOutputs(store->followLinksToStorePath(i), useOutput, forceRealise),
                     referrers, true, settings.gcKeepOutputs, settings.gcKeepDerivations);
             }
-            Roots roots = store->findRoots();
+            Roots roots = store->findRoots(false);
             for (auto & [target, links] : roots)
                 if (referrers.find(target) != referrers.end())
                     for (auto & link : links)
@@ -591,7 +591,7 @@ static void opGC(Strings opFlags, Strings opArgs)
     if (!opArgs.empty()) throw UsageError("no arguments expected");
 
     if (printRoots) {
-        Roots roots = store->findRoots();
+        Roots roots = store->findRoots(false);
         for (auto & [target, links] : roots)
             for (auto & link : links)
                 cout << link << " -> " << target << std::endl;