Custom C main instead of wrapper binaryHEADmasterdevel

Changelog: Use custom C main instead of wrapper binary for unshare(2) call.

1 files changed, 81 insertions, 0 deletions

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;
+}