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    SubjectRe: [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@canonical.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@canonical.com>
    > CC: Kees Cook <keescook@chromium.org>
    > CC: Will Drewry <wad@chromium.org>
    > CC: Oleg Nesterov <oleg@redhat.com>
    > CC: Andy Lutomirski <luto@amacapital.net>
    > CC: Pavel Emelyanov <xemul@parallels.com>
    > CC: Serge E. Hallyn <serge.hallyn@ubuntu.com>
    > CC: Alexei Starovoitov <ast@kernel.org>
    > CC: Daniel Borkmann <daniel@iogearbox.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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