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SubjectRe: [PATCH v2 4/4] samples: Add example of using PTRACE_GETFD in conjunction with user trap
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On December 9, 2019 8:30:00 PM GMT+01:00, Oleg Nesterov <oleg@redhat.com> wrote:
>On 12/09, Sargun Dhillon wrote:
>>
>> +#define CHILD_PORT_TRY_BIND 80
>> +#define CHILD_PORT_ACTUAL_BIND 4998
>
>...
>
>> +static int handle_req(int listener)
>> +{
>> + struct sockaddr_in addr = {
>> + .sin_family = AF_INET,
>> + .sin_port = htons(4998),
>
>then I think
> .sin_port = htons(CHILD_PORT_ACTUAL_BIND);
>
>would be more clear...
>
>> + .sin_addr = {
>> + .s_addr = htonl(INADDR_LOOPBACK)
>> + }
>> + };
>> + struct ptrace_getfd_args getfd_args = {
>> + .options = PTRACE_GETFD_O_CLOEXEC
>> + };
>> + struct seccomp_notif_sizes sizes;
>> + struct seccomp_notif_resp *resp;
>> + struct seccomp_notif *req;
>> + int fd, ret = 1;
>> +
>> + if (seccomp(SECCOMP_GET_NOTIF_SIZES, 0, &sizes) < 0) {
>> + perror("seccomp(GET_NOTIF_SIZES)");
>> + goto out;
>> + }
>> + req = malloc(sizes.seccomp_notif);
>> + if (!req)
>> + goto out;
>> + memset(req, 0, sizeof(*req));
>> +
>> + resp = malloc(sizes.seccomp_notif_resp);
>> + if (!resp)
>> + goto out_free_req;
>> + memset(resp, 0, sizeof(*resp));
>> +
>> + if (ioctl(listener, SECCOMP_IOCTL_NOTIF_RECV, req)) {
>> + perror("ioctl recv");
>> + goto out;
>> + }
>> + printf("Child tried to call bind with fd: %lld\n",
>req->data.args[0]);
>> + getfd_args.fd = req->data.args[0];
>> + fd = ptrace_getfd(req->pid, &getfd_args);
>
>and iiuc otherwise you do not need to ptrace the child. So you could
>remove
>ptrace(PTRACE_SEIZE) in main() and just do
>
> ptrace(PTRACE_SEIZE, req->pid);
> fd = ptrace_getfd(req->pid, &getfd_args);
> ptrace(PTRACE_DETACH, req->pid);
>
>here. However, PTRACE_DETACH won't work, it needs the stopped tracee.
>We can
>add PTRACE_DETACH_ASYNC, but this makes me think that PTRACE_GETFD has
>nothing
>to do with ptrace.
>
>May be a new syscall which does ptrace_may_access() + get_task_file()
>will make
>more sense?
>
>Oleg.

Once more since this annoying app uses html by default...

But we can already do this right now and this is just an improvement.
That's a bit rich for a new syscall imho...

Christian

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