From a06801de17fab47b68300c6736cd031fb0d25b6e Mon Sep 17 00:00:00 2001
From: edef <edef@edef.eu>
Date: Wed, 4 Oct 2023 16:50:24 +0000
Subject: [PATCH] StorePath: reject names starting with '.'

This has been the behaviour before Nix 2.4. It was dropped in a rewrite
in 759947bf72c134592f0ce23d385e48095bd0a301, allowing the creation of
store paths that aren't considered valid by older Nix versions or other
Nix tooling.

Nix 2.4 didn't ship in NixOS until 22.05, and stdenv.mkDerivation in
nixpkgs drops leading periods since April 2022, so it's unlikely anyone
is relying on the current lax behaviour.

Closes #9091.

Change-Id: I4a57bd9899e1b0dba56870ae5a1b680918a18ce9
---
 src/libstore/path-regex.hh | 2 +-
 src/libstore/path.cc       | 2 ++
 src/libstore/tests/path.cc | 9 +++++++--
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/libstore/path-regex.hh b/src/libstore/path-regex.hh
index 4f8dc4c1f..a44e6a2eb 100644
--- a/src/libstore/path-regex.hh
+++ b/src/libstore/path-regex.hh
@@ -3,6 +3,6 @@
 
 namespace nix {
 
-static constexpr std::string_view nameRegexStr = R"([0-9a-zA-Z\+\-\._\?=]+)";
+static constexpr std::string_view nameRegexStr = R"([0-9a-zA-Z\+\-_\?=][0-9a-zA-Z\+\-\._\?=]*)";
 
 }
diff --git a/src/libstore/path.cc b/src/libstore/path.cc
index 552e83114..3c6b9fc10 100644
--- a/src/libstore/path.cc
+++ b/src/libstore/path.cc
@@ -11,6 +11,8 @@ static void checkName(std::string_view path, std::string_view name)
     if (name.size() > StorePath::MaxPathLen)
         throw BadStorePath("store path '%s' has a name longer than %d characters",
             path, StorePath::MaxPathLen);
+    if (name[0] == '.')
+        throw BadStorePath("store path '%s' starts with illegal character '.'", path);
     // See nameRegexStr for the definition
     for (auto c : name)
         if (!((c >= '0' && c <= '9')
diff --git a/src/libstore/tests/path.cc b/src/libstore/tests/path.cc
index 430aa0099..e9ecba22e 100644
--- a/src/libstore/tests/path.cc
+++ b/src/libstore/tests/path.cc
@@ -39,6 +39,7 @@ TEST_DONT_PARSE(double_star, "**")
 TEST_DONT_PARSE(star_first, "*,foo")
 TEST_DONT_PARSE(star_second, "foo,*")
 TEST_DONT_PARSE(bang, "foo!o")
+TEST_DONT_PARSE(dotfile, ".gitignore")
 
 #undef TEST_DONT_PARSE
 
@@ -101,8 +102,12 @@ Gen<StorePathName> Arbitrary<StorePathName>::arbitrary()
                 pre += '-';
                 break;
             case 64:
-                pre += '.';
-                break;
+                // names aren't permitted to start with a period,
+                // so just fall through to the next case here
+                if (c != 0) {
+                    pre += '.';
+                    break;
+                }
             case 65:
                 pre += '_';
                 break;