From 0c8bad166577f9973ba5701aee5ca5d9a3f3bc5d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roman=20Smr=C5=BE?= <roman.smrz@seznam.cz>
Date: Sun, 13 Oct 2024 16:50:13 +0200
Subject: Custom C main instead of wrapper binary

Changelog: Use custom C main instead of wrapper binary for unshare(2) call.
---
 src/Main.hs    |  4 +++
 src/Wrapper.hs | 45 --------------------------------
 src/main.c     | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 85 insertions(+), 45 deletions(-)
 delete mode 100644 src/Wrapper.hs
 create mode 100644 src/main.c

(limited to 'src')

diff --git a/src/Main.hs b/src/Main.hs
index 42b2e5b..01bb766 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -157,3 +157,7 @@ main = do
     ok <- allM (uncurry $ runTest out $ optTest opts) $
         concat $ replicate (optRepeat opts) $ concat tests
     when (not ok) exitFailure
+
+foreign export ccall testerMain :: IO ()
+testerMain :: IO ()
+testerMain = main
diff --git a/src/Wrapper.hs b/src/Wrapper.hs
deleted file mode 100644
index 544e37c..0000000
--- a/src/Wrapper.hs
+++ /dev/null
@@ -1,45 +0,0 @@
-module Main where
-
-import Control.Monad
-
-import GHC.Environment
-
-import System.Directory
-import System.Environment
-import System.FilePath
-import System.Linux.Namespaces
-import System.Posix.Process
-import System.Posix.User
-import System.Process
-
-main :: IO ()
-main = do
-    -- we must get uid/gid before unshare
-    uid <- getEffectiveUserID
-    gid <- getEffectiveGroupID
-
-    unshare [User, Network, Mount]
-    writeUserMappings Nothing [UserMapping 0 uid 1]
-    writeGroupMappings Nothing [GroupMapping 0 gid 1] True
-
-    -- needed for creating /run/netns
-    callCommand "mount -t tmpfs tmpfs /run"
-
-    epath <- takeDirectory <$> getExecutablePath -- directory containing executable
-    fpath <- map takeDirectory . filter (any isPathSeparator) . take 1 <$> getFullArgs
-        -- directory used for invocation, can differ from above for symlinked executable
-
-    let dirs = concat
-            [ [ epath ]
-            , [ epath </> "../../../erebos-tester-core/build/erebos-tester-core" ]
-            , fpath
-            ]
-
-    args <- getArgs
-    mapM_ (\file -> executeFile file False args Nothing) =<<
-        findExecutablesInDirectories dirs "erebos-tester-core"
-    when (null fpath) $
-        mapM_ (\file -> executeFile file False args Nothing) =<<
-            findExecutables "erebos-tester-core"
-
-    fail "core binary not found"
diff --git a/src/main.c b/src/main.c
new file mode 100644
index 0000000..98daf2c
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,81 @@
+#include "HsFFI.h"
+
+#if defined(__GLASGOW_HASKELL__)
+#include "Main_stub.h"
+#endif
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/mount.h>
+#include <unistd.h>
+
+/*
+ * The unshare call with CLONE_NEWUSER needs to happen before starting
+ * additional threads, which means before initializing the Haskell RTS.
+ * To achieve that, replace Haskell main with a custom one here that does
+ * the unshare work and then executes the Haskell code.
+ */
+
+static bool writeProcSelfFile( const char * file, const char * data, size_t size )
+{
+	char path[ 256 ];
+	if( snprintf( path, sizeof( path ), "/proc/self/%s", file )
+			>= sizeof( path ) ){
+		fprintf( stderr, "buffer too small\n" );
+		return false;
+	}
+
+	int fd = open( path, O_WRONLY );
+	if( fd < 0 ){
+		fprintf( stderr, "failed to open %s: %s", path, strerror( errno ));
+		return false;
+	}
+
+	ssize_t written = write( fd, data, size );
+	if( written < 0 )
+		fprintf( stderr, "failed to write to %s: %s\n", path, strerror( errno ));
+
+	close( fd );
+	return written == size;
+}
+
+int main( int argc, char * argv[] )
+{
+	uid_t uid = geteuid();
+	gid_t gid = getegid();
+	unshare( CLONE_NEWUSER | CLONE_NEWNET | CLONE_NEWNS );
+
+	char buf[ 256 ];
+	int len;
+
+	len = snprintf( buf, sizeof( buf ), "%d %d %d\n", 0, uid, 1 );
+	if( len >= sizeof( buf ) ){
+		fprintf( stderr, "buffer too small\n" );
+		return 1;
+	}
+	if ( ! writeProcSelfFile( "uid_map", buf, len ) )
+		return 1;
+
+	if ( ! writeProcSelfFile( "setgroups", "deny\n", 5 ) )
+		return 1;
+
+	len = snprintf( buf, sizeof( buf ), "%d %d %d\n", 0, gid, 1 );
+	if( len >= sizeof( buf ) ){
+		fprintf( stderr, "buffer too small\n" );
+		return 1;
+	}
+	if ( ! writeProcSelfFile( "gid_map", buf, len ) )
+		return 1;
+
+	mount( "tmpfs", "/run", "tmpfs", 0, "size=4m" );
+
+	hs_init( &argc, &argv );
+	testerMain();
+	hs_exit();
+
+	return 0;
+}
-- 
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