Messages in this thread | | | From | (Eric W. Biederman) | Date | Thu, 26 Mar 2020 07:54:04 -0500 | Subject | Re: [PATCH V2] ipc/mqueue.c: change __do_notify() to bypass check_kill_permission() |
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Oleg Nesterov <oleg@redhat.com> writes:
> Commit cc731525f26a ("signal: Remove kernel interal si_code magic") > changed the value of SI_FROMUSER(SI_MESGQ), this means that mq_notify() > no longer works if the sender doesn't have rights to send a signal. > > Change __do_notify() to use do_send_sig_info() instead of kill_pid_info() > to avoid check_kill_permission(). > > This needs the additional notify.sigev_signo != 0 check, shouldn't we > change do_mq_notify() to deny sigev_signo == 0 ? > > Test-case: > > #include <signal.h> > #include <mqueue.h> > #include <unistd.h> > #include <sys/wait.h> > #include <assert.h> > > static int notified; > > static void sigh(int sig) > { > notified = 1; > } > > int main(void) > { > signal(SIGIO, sigh); > > int fd = mq_open("/mq", O_RDWR|O_CREAT, 0666, NULL); > assert(fd >= 0); > > struct sigevent se = { > .sigev_notify = SIGEV_SIGNAL, > .sigev_signo = SIGIO, > }; > assert(mq_notify(fd, &se) == 0); > > if (!fork()) { > assert(setuid(1) == 0); > mq_send(fd, "",1,0); > return 0; > } > > wait(NULL); > mq_unlink("/mq"); > assert(notified); > return 0; > } > > Reported-by: Yoji <yoji.fujihar.min@gmail.com> > Fixes: cc731525f26a ("signal: Remove kernel interal si_code magic") > Cc: stable <stable@vger.kernel.org> > Signed-off-by: Oleg Nesterov <oleg@redhat.com> > --- > ipc/mqueue.c | 28 ++++++++++++++++++++-------- > 1 file changed, 20 insertions(+), 8 deletions(-) > > diff --git a/ipc/mqueue.c b/ipc/mqueue.c > index 49a05ba3000d..63b164932ffd 100644 > --- a/ipc/mqueue.c > +++ b/ipc/mqueue.c > @@ -774,28 +774,40 @@ static void __do_notify(struct mqueue_inode_info *info) > * synchronously. */ > if (info->notify_owner && > info->attr.mq_curmsgs == 1) { > - struct kernel_siginfo sig_i; > switch (info->notify.sigev_notify) { > case SIGEV_NONE: > break; > - case SIGEV_SIGNAL: > - /* sends signal */ > + case SIGEV_SIGNAL: { > + struct kernel_siginfo sig_i; > + struct task_struct *task; > + > + /* do_mq_notify() accepts sigev_signo == 0, why?? */ > + if (!info->notify.sigev_signo) > + break; > > clear_siginfo(&sig_i); > sig_i.si_signo = info->notify.sigev_signo; > sig_i.si_errno = 0; > sig_i.si_code = SI_MESGQ; > sig_i.si_value = info->notify.sigev_value; > - /* map current pid/uid into info->owner's namespaces */ > rcu_read_lock(); > + /* map current pid/uid into info->owner's namespaces */ > sig_i.si_pid = task_tgid_nr_ns(current, > ns_of_pid(info->notify_owner)); > - sig_i.si_uid = from_kuid_munged(info->notify_user_ns, current_uid()); > + sig_i.si_uid = from_kuid_munged(info->notify_user_ns, > + current_uid()); > + /* > + * We can't use kill_pid_info(), this signal should > + * bypass check_kill_permission(). It is from kernel > + * but si_fromuser() can't know this. > + */ > + task = pid_task(info->notify_owner, PIDTYPE_PID); ^^^^^^^^^^^^ Minor nit: If we are doing the task lookup ourselves that can and should be PIDTYPE_TGID. Because the code captures the TGID itself none of the very valid backwards compatibility reasons for using PIDTYPE_PID come into play.
> + if (task) > + do_send_sig_info(info->notify.sigev_signo, > + &sig_i, task, PIDTYPE_TGID); > rcu_read_unlock(); > - > - kill_pid_info(info->notify.sigev_signo, > - &sig_i, info->notify_owner); > break; > + } > case SIGEV_THREAD: > set_cookie(info->notify_cookie, NOTIFY_WOKENUP); > netlink_sendskb(info->notify_sock, info->notify_cookie); Eric
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