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>

1 files changed, 21 insertions, 0 deletions

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);