Security: Don't allow builders to change permissions on files they don't own
It turns out that in multi-user Nix, a builder may be able to do ln /etc/shadow $out/foo Afterwards, canonicalisePathMetaData() will be applied to $out/foo, causing /etc/shadow's mode to be set to 444 (readable by everybody but writable by nobody). That's obviously Very Bad. Fortunately, this fails in NixOS's default configuration because /nix/store is a bind mount, so "ln" will fail with "Invalid cross-device link". It also fails if hard-link restrictions are enabled, so a workaround is: echo 1 > /proc/sys/fs/protected_hardlinks The solution is to check that all files in $out are owned by the build user. This means that innocuous operations like "ln ${pkgs.foo}/some-file $out/" are now rejected, but that already failed in chroot builds anyway.
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@ -2287,7 +2287,7 @@ void DerivationGoal::computeClosure()
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}
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/* Get rid of all weird permissions. */
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canonicalisePathMetaData(path);
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canonicalisePathMetaData(path, buildUser.enabled() ? buildUser.getUID() : -1);
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/* For this output path, find the references to other paths
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contained in it. Compute the SHA-256 NAR hash at the same
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@ -2839,7 +2839,7 @@ void SubstitutionGoal::finished()
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return;
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}
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canonicalisePathMetaData(destPath);
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canonicalisePathMetaData(destPath, -1);
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worker.store.optimisePath(destPath); // FIXME: combine with hashPath()
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@ -465,7 +465,7 @@ void LocalStore::makeStoreWritable()
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const time_t mtimeStore = 1; /* 1 second into the epoch */
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void canonicalisePathMetaData(const Path & path, bool recurse)
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void canonicalisePathMetaData(const Path & path, bool recurse, uid_t fromUid)
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{
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checkInterrupt();
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@ -477,6 +477,9 @@ void canonicalisePathMetaData(const Path & path, bool recurse)
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has already been checked in dumpPath(). */
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assert(S_ISREG(st.st_mode) || S_ISDIR(st.st_mode) || S_ISLNK(st.st_mode));
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if (fromUid != (uid_t) -1 && st.st_uid != fromUid)
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throw BuildError(format("invalid ownership on file `%1%'") % path);
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/* Change ownership to the current uid. If it's a symlink, use
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lchown if available, otherwise don't bother. Wrong ownership
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of a symlink doesn't matter, since the owning user can't change
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@ -529,14 +532,14 @@ void canonicalisePathMetaData(const Path & path, bool recurse)
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if (recurse && S_ISDIR(st.st_mode)) {
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Strings names = readDirectory(path);
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foreach (Strings::iterator, i, names)
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canonicalisePathMetaData(path + "/" + *i, true);
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canonicalisePathMetaData(path + "/" + *i, true, fromUid);
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}
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}
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void canonicalisePathMetaData(const Path & path)
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void canonicalisePathMetaData(const Path & path, uid_t fromUid)
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{
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canonicalisePathMetaData(path, true);
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canonicalisePathMetaData(path, true, fromUid);
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/* On platforms that don't have lchown(), the top-level path can't
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be a symlink, since we can't change its ownership. */
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@ -1198,7 +1201,7 @@ Path LocalStore::addToStoreFromDump(const string & dump, const string & name,
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} else
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writeFile(dstPath, dump);
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canonicalisePathMetaData(dstPath);
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canonicalisePathMetaData(dstPath, -1);
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/* Register the SHA-256 hash of the NAR serialisation of
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the path in the database. We may just have computed it
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@ -1263,7 +1266,7 @@ Path LocalStore::addTextToStore(const string & name, const string & s,
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writeFile(dstPath, s);
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canonicalisePathMetaData(dstPath);
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canonicalisePathMetaData(dstPath, -1);
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HashResult hash = hashPath(htSHA256, dstPath);
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@ -1498,7 +1501,7 @@ Path LocalStore::importPath(bool requireSignature, Source & source)
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throw SysError(format("cannot move `%1%' to `%2%'")
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% unpacked % dstPath);
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canonicalisePathMetaData(dstPath);
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canonicalisePathMetaData(dstPath, -1);
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/* !!! if we were clever, we could prevent the hashPath()
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here. */
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@ -307,9 +307,9 @@ private:
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without execute permission; setuid bits etc. are cleared)
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- the owner and group are set to the Nix user and group, if we're
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in a setuid Nix installation. */
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void canonicalisePathMetaData(const Path & path);
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void canonicalisePathMetaData(const Path & path, uid_t fromUid);
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void canonicalisePathMetaData(const Path & path, bool recurse);
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void canonicalisePathMetaData(const Path & path, bool recurse, uid_t fromUid);
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MakeError(PathInUse, Error);
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@ -32,7 +32,7 @@ struct MakeReadOnly
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{
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try {
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/* This will make the path read-only. */
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if (path != "") canonicalisePathMetaData(path, false);
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if (path != "") canonicalisePathMetaData(path, false, -1);
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} catch (...) {
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ignoreException();
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}
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@ -238,12 +238,6 @@ static void printTree(const Path & path,
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PathSet references;
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store->queryReferences(path, references);
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#if 0
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for (PathSet::iterator i = drv.inputSrcs.begin();
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i != drv.inputSrcs.end(); ++i)
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cout << format("%1%%2%\n") % (tailPad + treeConn) % *i;
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#endif
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/* Topologically sort under the relation A < B iff A \in
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closure(B). That is, if derivation A is an (possibly indirect)
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input of B, then A is printed first. This has the effect of
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@ -251,7 +245,7 @@ static void printTree(const Path & path,
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Paths sorted = topoSortPaths(*store, references);
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reverse(sorted.begin(), sorted.end());
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for (Paths::iterator i = sorted.begin(); i != sorted.end(); ++i) {
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foreach (Paths::iterator, i, sorted) {
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Paths::iterator j = i; ++j;
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printTree(*i, tailPad + treeConn,
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j == sorted.end() ? tailPad + treeNull : tailPad + treeLine,
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@ -521,7 +515,7 @@ static void registerValidity(bool reregister, bool hashGiven, bool canonicalise)
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if (!store->isValidPath(info.path) || reregister) {
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/* !!! races */
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if (canonicalise)
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canonicalisePathMetaData(info.path);
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canonicalisePathMetaData(info.path, -1);
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if (!hashGiven) {
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HashResult hash = hashPath(htSHA256, info.path);
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info.hash = hash.first;
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