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Message-ID: <CAKgNAki99ZFgLPE5mWWjj1nvdNyke1w0ttqmiG+Uk0rVfqutZw@mail.gmail.com>
Date:	Fri, 11 Sep 2015 14:08:50 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Tycho Andersen <tycho.andersen@...onical.com>
Cc:	Kees Cook <keescook@...omium.org>,
	Alexei Starovoitov <ast@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Will Drewry <wad@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Pavel Emelyanov <xemul@...allels.com>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	lkml <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2 4/5] seccomp: add a way to access filters via bpf fds

HI Tycho

On 11 September 2015 at 02:21, Tycho Andersen
<tycho.andersen@...onical.com> wrote:
> This patch adds a way for a process that is "real root" to access the
> seccomp filters of another process. The process first does a
> PTRACE_SECCOMP_GET_FILTER_FD to get an fd with that process' seccomp filter
> attached, and then iterates on this with PTRACE_SECCOMP_NEXT_FILTER using
> bpf(BPF_PROG_DUMP) to dump the actual program at each step.

Do you have a man- page patch for this change?

Cheers,

Michael

> Signed-off-by: Tycho Andersen <tycho.andersen@...onical.com>
> CC: Kees Cook <keescook@...omium.org>
> CC: Will Drewry <wad@...omium.org>
> CC: Oleg Nesterov <oleg@...hat.com>
> CC: Andy Lutomirski <luto@...capital.net>
> CC: Pavel Emelyanov <xemul@...allels.com>
> CC: Serge E. Hallyn <serge.hallyn@...ntu.com>
> CC: Alexei Starovoitov <ast@...nel.org>
> CC: Daniel Borkmann <daniel@...earbox.net>
> ---
>  include/linux/bpf.h         | 12 ++++++++++
>  include/linux/seccomp.h     | 14 +++++++++++
>  include/uapi/linux/ptrace.h |  3 +++
>  kernel/bpf/syscall.c        | 26 ++++++++++++++++++++-
>  kernel/ptrace.c             |  7 ++++++
>  kernel/seccomp.c            | 57 +++++++++++++++++++++++++++++++++++++++++++++
>  6 files changed, 118 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index f57d7fe..bfd9cab 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -162,6 +162,8 @@ void bpf_register_prog_type(struct bpf_prog_type_list *tl);
>  void bpf_register_map_type(struct bpf_map_type_list *tl);
>
>  struct bpf_prog *bpf_prog_get(u32 ufd);
> +int bpf_prog_set(u32 ufd, struct bpf_prog *new);
> +int bpf_new_fd(struct bpf_prog *prog, int flags);
>  void bpf_prog_put(struct bpf_prog *prog);
>  void bpf_prog_put_rcu(struct bpf_prog *prog);
>
> @@ -180,6 +182,16 @@ static inline struct bpf_prog *bpf_prog_get(u32 ufd)
>         return ERR_PTR(-EOPNOTSUPP);
>  }
>
> +static inline int bpf_prog_set(u32 ufd, struct bpf_prog *new)
> +{
> +       return -EINVAL;
> +}
> +
> +static inline int bpf_new_fd(struct bpf_prog *prog, int flags)
> +{
> +       return -EINVAL;
> +}
> +
>  static inline void bpf_prog_put(struct bpf_prog *prog)
>  {
>  }
> diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
> index a19ddac..41b083c 100644
> --- a/include/linux/seccomp.h
> +++ b/include/linux/seccomp.h
> @@ -95,4 +95,18 @@ static inline void get_seccomp_filter(struct task_struct *tsk)
>         return;
>  }
>  #endif /* CONFIG_SECCOMP_FILTER */
> +
> +#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
> +extern long seccomp_get_filter_fd(struct task_struct *child);
> +extern long seccomp_next_filter(struct task_struct *child, u32 fd);
> +#else
> +static inline long seccomp_get_filter_fd(struct task_struct *child)
> +{
> +       return -EINVAL;
> +}
> +static inline long seccomp_next_filter(struct task_struct *child, u32 fd)
> +{
> +       return -EINVAL;
> +}
> +#endif /* CONFIG_SECCOMP_FILTER && CONFIG_CHECKPOINT_RESTORE */
>  #endif /* _LINUX_SECCOMP_H */
> diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
> index cf1019e..041c3c3 100644
> --- a/include/uapi/linux/ptrace.h
> +++ b/include/uapi/linux/ptrace.h
> @@ -23,6 +23,9 @@
>
>  #define PTRACE_SYSCALL           24
>
> +#define PTRACE_SECCOMP_GET_FILTER_FD   40
> +#define PTRACE_SECCOMP_NEXT_FILTER     41
> +
>  /* 0x4200-0x4300 are reserved for architecture-independent additions.  */
>  #define PTRACE_SETOPTIONS      0x4200
>  #define PTRACE_GETEVENTMSG     0x4201
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 58ae9f4..ac3ed1c 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -506,6 +506,30 @@ struct bpf_prog *bpf_prog_get(u32 ufd)
>  }
>  EXPORT_SYMBOL_GPL(bpf_prog_get);
>
> +int bpf_prog_set(u32 ufd, struct bpf_prog *new)
> +{
> +       struct fd f;
> +       struct bpf_prog *prog;
> +
> +       f = fdget(ufd);
> +
> +       prog = get_prog(f);
> +       if (!IS_ERR(prog) && prog)
> +               bpf_prog_put(prog);
> +
> +       atomic_inc(&new->aux->refcnt);
> +       f.file->private_data = new;
> +       fdput(f);
> +       return 0;
> +}
> +EXPORT_SYMBOL_GPL(bpf_prog_set);
> +
> +int bpf_new_fd(struct bpf_prog *prog, int flags)
> +{
> +       return anon_inode_getfd("bpf-prog", &bpf_prog_fops, prog, flags);
> +}
> +EXPORT_SYMBOL_GPL(bpf_new_fd);
> +
>  /* last field in 'union bpf_attr' used by this command */
>  #define        BPF_PROG_LOAD_LAST_FIELD kern_version
>
> @@ -572,7 +596,7 @@ static int bpf_prog_load(union bpf_attr *attr)
>         if (err < 0)
>                 goto free_used_maps;
>
> -       err = anon_inode_getfd("bpf-prog", &bpf_prog_fops, prog, O_RDWR | O_CLOEXEC);
> +       err = bpf_new_fd(prog, O_RDWR | O_CLOEXEC);
>         if (err < 0)
>                 /* failed to allocate fd */
>                 goto free_used_maps;
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index c8e0e05..a151c35 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -1003,6 +1003,13 @@ int ptrace_request(struct task_struct *child, long request,
>                 break;
>         }
>  #endif
> +
> +       case PTRACE_SECCOMP_GET_FILTER_FD:
> +               return seccomp_get_filter_fd(child);
> +
> +       case PTRACE_SECCOMP_NEXT_FILTER:
> +               return seccomp_next_filter(child, data);
> +
>         default:
>                 break;
>         }
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index afaeddf..1856f69 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -26,6 +26,8 @@
>  #endif
>
>  #ifdef CONFIG_SECCOMP_FILTER
> +#include <linux/bpf.h>
> +#include <uapi/linux/bpf.h>
>  #include <linux/filter.h>
>  #include <linux/pid.h>
>  #include <linux/ptrace.h>
> @@ -807,6 +809,61 @@ static inline long seccomp_set_mode_filter(unsigned int flags,
>  }
>  #endif
>
> +#if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
> +long seccomp_get_filter_fd(struct task_struct *child)
> +{
> +       long fd;
> +       struct seccomp_filter *filter;
> +
> +       if (!capable(CAP_SYS_ADMIN))
> +               return -EACCES;
> +
> +       if (child->seccomp.mode != SECCOMP_MODE_FILTER)
> +               return -EINVAL;
> +
> +       filter = child->seccomp.filter;
> +
> +       fd = bpf_new_fd(filter->prog, O_RDONLY);
> +       if (fd > 0)
> +               atomic_inc(&filter->prog->aux->refcnt);
> +
> +       return fd;
> +}
> +
> +long seccomp_next_filter(struct task_struct *child, u32 fd)
> +{
> +       struct seccomp_filter *cur;
> +       struct bpf_prog *prog;
> +       long ret = -ESRCH;
> +
> +       if (!capable(CAP_SYS_ADMIN))
> +               return -EACCES;
> +
> +       if (child->seccomp.mode != SECCOMP_MODE_FILTER)
> +               return -EINVAL;
> +
> +       prog = bpf_prog_get(fd);
> +       if (IS_ERR(prog)) {
> +               ret = PTR_ERR(prog);
> +               goto out;
> +       }
> +
> +       for (cur = child->seccomp.filter; cur; cur = cur->prev) {
> +               if (cur->prog == prog) {
> +                       if (!cur->prev)
> +                               ret = -ENOENT;
> +                       else
> +                               ret = bpf_prog_set(fd, cur->prev->prog);
> +                       break;
> +               }
> +       }
> +
> +out:
> +       bpf_prog_put(prog);
> +       return ret;
> +}
> +#endif
> +
>  /* Common entry point for both prctl and syscall. */
>  static long do_seccomp(unsigned int op, unsigned int flags,
>                        const char __user *uargs)
> --
> 2.1.4
>
> --
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-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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