libc: limit fd id allocations to FD_SETSIZE

fd > FD_SETSIZE cannot use 'select' or 'poll' within our libc.
Therefore, we added a bit allocator in order to allocate fd < FD_SETSIZE
(1024).

fixes #3568

repos/libports/include/libc-plugin/fd_alloc.h

@@ -20,6 +20,7 @@
 #include <os/path.h>
 #include <base/allocator.h>
 #include <base/id_space.h>
+#include <util/bit_allocator.h>
 #include <util/xml_generator.h>
 
 /* libc includes */
@@ -57,9 +58,6 @@ namespace Libc {
 		bool cloexec  = 0;  /* for 'fcntl' */
 		bool modified = false;
 
-		File_descriptor(Id_space &id_space, Plugin &plugin, Plugin_context &context)
-		: _elem(*this, id_space), plugin(&plugin), context(&context) { }
-
 		File_descriptor(Id_space &id_space, Plugin &plugin, Plugin_context &context,
 		                Id_space::Id id)
 		: _elem(*this, id_space, id), plugin(&plugin), context(&context) { }
@@ -80,6 +78,8 @@ namespace Libc {
 
 			Id_space _id_space;
 
+			Genode::Bit_allocator<MAX_NUM_FDS> _id_allocator;
+
 		public:
 
 			/**

repos/libports/src/lib/libc/fd_alloc.cc

@@ -61,10 +61,14 @@ File_descriptor *File_descriptor_allocator::alloc(Plugin *plugin,
 	Lock::Guard guard(_lock);
 
 	bool const any_fd = (libc_fd < 0);
-	if (any_fd)
+	Id_space::Id id {(unsigned)libc_fd};
-		return new (_alloc) File_descriptor(_id_space, *plugin, *context);
+
+	if (any_fd) {
+		id.value = _id_allocator.alloc();
+	} else {
+		_id_allocator.alloc_addr(addr_t(libc_fd));
+	}
 
-	Id_space::Id const id {(unsigned)libc_fd};
 	return new (_alloc) File_descriptor(_id_space, *plugin, *context, id);
 }
 
@@ -76,6 +80,7 @@ void File_descriptor_allocator::free(File_descriptor *fdo)
 	if (fdo->fd_path)
 		_alloc.free((void *)fdo->fd_path, ::strlen(fdo->fd_path) + 1);
 
+	_id_allocator.free(fdo->libc_fd);
 	destroy(_alloc, fdo);
 }
 

repos/libports/src/lib/libc/select.cc

@@ -169,6 +169,9 @@ static int selscan(int nfds,
 	if (out_writefds)  FD_ZERO(out_writefds);
 	if (out_exceptfds) FD_ZERO(out_exceptfds);
 
+	if (nfds > FD_SETSIZE)
+		return Libc::Errno(EINVAL);
+
 	for (Plugin *plugin = plugin_registry()->first();
 	     plugin;
 	     plugin = plugin->next()) {