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Put the chroot inside a directory that isn't group/world-accessible

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Previously, the .chroot directory had permission 750 or 755 (depending
on the uid-range system feature) and was owned by root/nixbld. This
makes it possible for any nixbld user (if uid-range is disabled) or
any user (if uid-range is enabled) to inspect the contents of the
chroot of an active build and maybe interfere with it (e.g. via /tmp
in the chroot, which has 1777 permission).

To prevent this, the root is now a subdirectory of .chroot, which has
permission 700 and is owned by root/root.
This commit is contained in:
Eelco Dolstra 2024-05-14 13:00:00 +02:00
parent d99c868b04
commit ede95b1fc1
2 changed files with 19 additions and 5 deletions
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14
src/libstore/unix/build/local-derivation-goal.cc
View file

@ -673,15 +673,19 @@ void LocalDerivationGoal::startBuilder()
environment using bind-mounts. We put it in the Nix store
so that the build outputs can be moved efficiently from the
chroot to their final location. */
chrootRootDir = worker.store.Store::toRealPath(drvPath) + ".chroot";
deletePath(chrootRootDir);
chrootParentDir = worker.store.Store::toRealPath(drvPath) + ".chroot";
deletePath(chrootParentDir);
/* Clean up the chroot directory automatically. */
autoDelChroot = std::make_shared<AutoDelete>(chrootRootDir);
autoDelChroot = std::make_shared<AutoDelete>(chrootParentDir);
printMsg(lvlChatty, "setting up chroot environment in '%1%'", chrootRootDir);
printMsg(lvlChatty, "setting up chroot environment in '%1%'", chrootParentDir);
if (mkdir(chrootParentDir.c_str(), 0700) == -1)
throw SysError("cannot create '%s'", chrootRootDir);
chrootRootDir = chrootParentDir + "/root";
// FIXME: make this 0700
if (mkdir(chrootRootDir.c_str(), buildUser && buildUser->getUIDCount() != 1 ? 0755 : 0750) == -1)
throw SysError("cannot create '%1%'", chrootRootDir);

10
src/libstore/unix/build/local-derivation-goal.hh
View file

@ -65,6 +65,16 @@ struct LocalDerivationGoal : public DerivationGoal
*/
bool useChroot = false;
/**
* The parent directory of `chrootRootDir`. It has permission 700
* and is owned by root to ensure other users cannot mess with
* `chrootRootDir`.
*/
Path chrootParentDir;
/**
* The root of the chroot environment.
*/
Path chrootRootDir;
/**