Re: [PATCH v2 4/5] seccomp: add a way to access filters via bpf fds
From: Michael Kerrisk (man-pages)
Date: Fri Sep 11 2015 - 08:09:17 EST
HI Tycho
On 11 September 2015 at 02:21, Tycho Andersen
<tycho.andersen@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> CC: Kees Cook <keescook@xxxxxxxxxxxx>
> CC: Will Drewry <wad@xxxxxxxxxxxx>
> CC: Oleg Nesterov <oleg@xxxxxxxxxx>
> CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> CC: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> CC: Serge E. Hallyn <serge.hallyn@xxxxxxxxxx>
> CC: Alexei Starovoitov <ast@xxxxxxxxxx>
> CC: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> ---
> 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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