[Patch v2] daemon: Set ownership of kept build directories to the calling user.

[Hartmut Goebel <h.goebel@crazy-compilers.com>]

Fixes <http://bugs.gnu.org/15890>.

* nix/libstore/globals.hh (Settings) Add clientUid and clientGid.
* nix/nix-daemon/nix-daemon.cc (pdaemonLoop] Store UID and GID of the
  caller in settings.
* nix/libstore/build.cc (_chown): New function.
  (DerivationGoal::deleteTmpDir): Use it, change ownership of build
  directory if it is kept.
---
 nix/libstore/build.cc        | 24 ++++++++++++++++++++++++
 nix/libstore/globals.hh      |  6 ++++++
 nix/nix-daemon/nix-daemon.cc | 13 +++++++++++++
 3 files changed, 43 insertions(+)

diff --git a/nix/libstore/build.cc b/nix/libstore/build.cc
index ae78e65..b49fb95 100644
--- a/nix/libstore/build.cc
+++ b/nix/libstore/build.cc
@@ -2609,6 +2609,23 @@ void DerivationGoal::closeLogFile()
 }
 
 
+static void _chown(const Path & path, uid_t uid, gid_t gid)
+{
+    checkInterrupt();
+
+    printMsg(lvlVomit, format("%1%") % path);
+
+    if (chown(path.c_str(), uid, gid) == -1) {
+	throw SysError(format("change owner and group of `%1%'") % path);
+    }
+    struct stat st = lstat(path);
+    if (S_ISDIR(st.st_mode)) {
+        for (auto & i : readDirectory(path))
+            _chown(path + "/" + i.name, uid, gid);
+    }
+}
+
+
 void DerivationGoal::deleteTmpDir(bool force)
 {
     if (tmpDir != "") {
@@ -2617,6 +2634,13 @@ void DerivationGoal::deleteTmpDir(bool force)
                 format("note: keeping build directory `%2%'")
                 % drvPath % tmpDir);
             chmod(tmpDir.c_str(), 0755);
+            // Change the ownership if clientUid is set. Never change the
+            // ownership to "root" for security reasons. So zero is used as
+            // marker for unset.
+            if (settings.clientUid != 0) {
+                _chown(tmpDir, settings.clientUid,
+                       settings.clientGid != 0 ? settings.clientGid : -1);
+            }
         }
         else
             deletePath(tmpDir);
diff --git a/nix/libstore/globals.hh b/nix/libstore/globals.hh
index 8c07e36..dc6a004 100644
--- a/nix/libstore/globals.hh
+++ b/nix/libstore/globals.hh
@@ -70,6 +70,12 @@ struct Settings {
        subgoal of the same goal) fails. */
     bool keepGoing;
 
+    /* User and groud id of the client issuing the buld request.  Used to set
+       the owner and group of the keept temporary directories of failed
+       builds. */
+    uid_t clientUid;
+    gid_t clientGid;
+
     /* Whether, if we cannot realise the known closure corresponding
        to a derivation, we should try to normalise the derivation
        instead. */
diff --git a/nix/nix-daemon/nix-daemon.cc b/nix/nix-daemon/nix-daemon.cc
index 35c284f..e900a7d 100644
--- a/nix/nix-daemon/nix-daemon.cc
+++ b/nix/nix-daemon/nix-daemon.cc
@@ -950,6 +950,19 @@ static void daemonLoop()
                     strncpy(argvSaved[1], processName.c_str(), strlen(argvSaved[1]));
                 }
 
+#if defined(SO_PEERCRED)
+                /* Store the client's user and group for this connection. This
+                   has to be done in the forked process since it is per
+                   connection. */
+                settings.clientUid = cred.uid;
+                settings.clientGid = cred.gid;
+#else
+                /* Setting these to zero means: do not change, esp. do not
+                   change to "root". */
+                settings.clientUid = 0;
+                settings.clientGid = 0;
+#endif
+
                 /* Handle the connection. */
                 from.fd = remote;
                 to.fd = remote;
-- 
2.7.4