modutils: support finit_module syscall

On some systems like Chromium OS, loading modules from non-verified
filesystems is denied.  Only finit_module is allowed because an open
fd is passed which can be checked against a verified location.

Change the module loading code to first attempt finit_module and if
that fails for whatever reason, fall back to the existing logic.

On x86_64, this adds ~80 bytes to modutils/modutils.o and ~68 bytes
to modutils/modprobe-small.o.

Signed-off-by: Mike Frysinger <vapier@chromium.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 51 insertions, 3 deletions

diff --git a/modutils/modprobe-small.c b/modutils/modprobe-small.c
index 5936e48cf..a47e52234 100644
--- a/modutils/modprobe-small.c
+++ b/modutils/modprobe-small.c
@@ -18,9 +18,13 @@
 /* After libbb.h, since it needs sys/types.h on some systems */
 #include <sys/utsname.h> /* uname() */
 #include <fnmatch.h>
+#include <sys/syscall.h>
 
 extern int init_module(void *module, unsigned long len, const char *options);
 extern int delete_module(const char *module, unsigned flags);
+#ifdef __NR_finit_module
+# define finit_module(fd, uargs, flags) syscall(__NR_finit_module, fd, uargs, flags)
+#endif
 /* linux/include/linux/module.h has limit of 64 chars on module names */
 #undef MODULE_NAME_LEN
 #define MODULE_NAME_LEN 64
@@ -209,11 +213,34 @@ static int load_module(const char *fname, const char *options)
 	int r;
 	size_t len = MAXINT(ssize_t);
 	char *module_image;
+
+	if (!options)
+		options = "";
+
 	dbg1_error_msg("load_module('%s','%s')", fname, options);
 
-	module_image = xmalloc_open_zipped_read_close(fname, &len);
-	r = (!module_image || init_module(module_image, len, options ? options : "") != 0);
-	free(module_image);
+	/*
+	 * First we try finit_module if available.  Some kernels are configured
+	 * to only allow loading of modules off of secure storage (like a read-
+	 * only rootfs) which needs the finit_module call.  If it fails, we fall
+	 * back to normal module loading to support compressed modules.
+	 */
+	r = 1;
+# ifdef __NR_finit_module
+	{
+		int fd = open(fname, O_RDONLY | O_CLOEXEC);
+		if (fd >= 0) {
+			r = finit_module(fd, options, 0) != 0;
+			close(fd);
+		}
+	}
+# endif
+	if (r != 0) {
+		module_image = xmalloc_open_zipped_read_close(fname, &len);
+		r = (!module_image || init_module(module_image, len, options) != 0);
+		free(module_image);
+	}
+
 	dbg1_error_msg("load_module:%d", r);
 	return r; /* 0 = success */
 #else
diff --git a/modutils/modutils.c b/modutils/modutils.c
index 0a056731d..d36caaf68 100644
--- a/modutils/modutils.c
+++ b/modutils/modutils.c
@@ -13,6 +13,9 @@ extern int delete_module(const char *module, unsigned int flags);
 #else
 # include <sys/syscall.h>
 # define init_module(mod, len, opts) syscall(__NR_init_module, mod, len, opts)
+# if defined(__NR_finit_module)
+#  define finit_module(fd, uargs, flags) syscall(__NR_finit_module, fd, uargs, flags)
+# endif
 # define delete_module(mod, flags) syscall(__NR_delete_module, mod, flags)
 #endif
 
@@ -212,6 +215,24 @@ int FAST_FUNC bb_init_module(const char *filename, const char *options)
 		return bb_init_module_24(filename, options);
 #endif
 
+	/*
+	 * First we try finit_module if available.  Some kernels are configured
+	 * to only allow loading of modules off of secure storage (like a read-
+	 * only rootfs) which needs the finit_module call.  If it fails, we fall
+	 * back to normal module loading to support compressed modules.
+	 */
+# ifdef __NR_finit_module
+	{
+		int fd = open(filename, O_RDONLY | O_CLOEXEC);
+		if (fd >= 0) {
+			rc = finit_module(fd, options, 0) != 0;
+			close(fd);
+			if (rc == 0)
+				return rc;
+		}
+	}
+# endif
+
 	image_size = INT_MAX - 4095;
 	mmaped = 0;
 	image = try_to_mmap_module(filename, &image_size);