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List:       busybox
Subject:    Re: [PATCH] modutils: support finit_module syscall
From:       Denys Vlasenko <vda.linux () googlemail ! com>
Date:       2016-09-15 10:17:05
Message-ID: CAK1hOcOOWsEw6ReZvxdvkufJkPqOsmHcXQiQQudLo3juSLzEKw () mail ! gmail ! com
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Applied, thanks!

On Tue, Sep 13, 2016 at 11:06 PM, Mike Frysinger <vapier@gentoo.org> wrote:
> From: Mike Frysinger <vapier@chromium.org>
>
> 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>
> ---
>  modutils/modprobe-small.c | 36 ++++++++++++++++++++++++++++++++----
>  modutils/modutils.c       | 19 +++++++++++++++++++
>  2 files changed, 51 insertions(+), 4 deletions(-)
>
> diff --git a/modutils/modprobe-small.c b/modutils/modprobe-small.c
> index 5936e48cff79..456b43aa35c0 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
> @@ -206,14 +210,38 @@ static const char *moderror(int err)
>  static int load_module(const char *fname, const char *options)
>  {
>  #if 1
> -       int r;
> +       int r = 1;
>         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.
> +        */
> +# ifdef __NR_finit_module
> +       {
> +               int fd = open(fname, O_RDONLY | O_CLOEXEC);
> +               if (fd >= 0) {
> +                       r = finit_module(fd, options, 0) != 0;
> +                       close(fd);
> +               } else
> +                       r = -1;
> +       }
> +# 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 0a056731d2ad..38d4e15a194a 100644
> --- a/modutils/modutils.c
> +++ b/modutils/modutils.c
> @@ -13,6 +13,7 @@ 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)
> +# define finit_module(fd, uargs, flags) syscall(__NR_finit_module, fd, uargs, flags)
>  # define delete_module(mod, flags) syscall(__NR_delete_module, mod, flags)
>  #endif
>
> @@ -212,6 +213,24 @@ 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);
> --
> 2.9.0
>
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