On Sep 11, 2015 9:44 AM, "Tycho Andersen" [off-list ref] wrote:
On Fri, Sep 11, 2015 at 09:20:55AM -0700, Andy Lutomirski wrote:
quoted
On Sep 10, 2015 5:22 PM, "Tycho Andersen" [off-list ref] wrote:
quoted
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.
quoted
+
+ fd = bpf_new_fd(filter->prog, O_RDONLY);
+ if (fd > 0)
+ atomic_inc(&filter->prog->aux->refcnt);
Why isn't this folded into bpf_new_fd?
No reason it can't be as far as I can see. I'll make the change for
the next version.
quoted
quoted
+
+ 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);
This lets you take an fd pointing to one prog and point it elsewhere.
I'm not sure that's a good idea.
That's how the interface was designed (calling ptrace(NEXT_FILTER, fd) and
then doing bpf(DUMP, fd)). I suppose we could have NEXT_FILTER return
a new fd instead if that seems better to you.
It'll be slower, but it avoids a weird side effect.
Tycho