Re: + make-good_sigevent-non-static.patch added to -mm tree

Re: + make-good_sigevent-non-static.patch added to -mm tree

[Oleg Nesterov]

SИbastien DuguИ wrote:
>
> +struct task_struct *good_sigevent(sigevent_t *event)
> +{
> +	struct task_struct *task = current->group_leader;
> +
> +	if ((event->sigev_notify & SIGEV_THREAD_ID) == SIGEV_THREAD_ID) {
> +		task = find_task_by_pid(event->sigev_notify_thread_id);
> +
> +		if (!task || task->tgid != current->tgid)
> +			return NULL;
> +	} else if (event->sigev_notify == SIGEV_SIGNAL) {

No, no, we can't use "else" here,

> +		if (event->sigev_signo <= 0 || event->sigev_signo > SIGRTMAX)

because we skip the check above in SIGEV_THREAD_ID case.

This way any user can crash the kernel with a minimal effort.

Oleg.

Re: + make-good_sigevent-non-static.patch added to -mm tree

[Sébastien Dugué]

On Thu, 25 Jan 2007 18:43:24 +0300 Oleg Nesterov <oleg@tv-sign.ru> wrote:

> SИbastien DuguИ wrote:
> >
> > +struct task_struct *good_sigevent(sigevent_t *event)
> > +{
> > +	struct task_struct *task = current->group_leader;
> > +
> > +	if ((event->sigev_notify & SIGEV_THREAD_ID) == SIGEV_THREAD_ID) {
> > +		task = find_task_by_pid(event->sigev_notify_thread_id);
> > +
> > +		if (!task || task->tgid != current->tgid)
> > +			return NULL;
> > +	} else if (event->sigev_notify == SIGEV_SIGNAL) {
> 
> No, no, we can't use "else" here,
> 
> > +		if (event->sigev_signo <= 0 || event->sigev_signo > SIGRTMAX)
> 
> because we skip the check above in SIGEV_THREAD_ID case.

  Right, will fix this.

> 
> This way any user can crash the kernel with a minimal effort.

  Well I tried, no crash, just the signal failing to be delivered.

  Thanks,

  Sébastien.

Re: + make-good_sigevent-non-static.patch added to -mm tree

[Oleg Nesterov]

On 01/26, S?bastien Dugu? wrote:
>
> On Thu, 25 Jan 2007 18:43:24 +0300 Oleg Nesterov <oleg@tv-sign.ru> wrote:
> 
> > SИbastien DuguИ wrote:
> > >
> > > +struct task_struct *good_sigevent(sigevent_t *event)
> > > +{
> > > +	struct task_struct *task = current->group_leader;
> > > +
> > > +	if ((event->sigev_notify & SIGEV_THREAD_ID) == SIGEV_THREAD_ID) {
> > > +		task = find_task_by_pid(event->sigev_notify_thread_id);
> > > +
> > > +		if (!task || task->tgid != current->tgid)
> > > +			return NULL;
> > > +	} else if (event->sigev_notify == SIGEV_SIGNAL) {
> > 
> > No, no, we can't use "else" here,
> > 
> > > +		if (event->sigev_signo <= 0 || event->sigev_signo > SIGRTMAX)
> > 
> > because we skip the check above in SIGEV_THREAD_ID case.
> 
>   Right, will fix this.
> 
> > 
> > This way any user can crash the kernel with a minimal effort.
> 
>   Well I tried, no crash, just the signal failing to be delivered.

	sigaddset:

		set->sig[sig / _NSIG_BPW] |= 1UL << (sig % _NSIG_BPW);

This writes to ->sig[event->sigev_signo / _NSIG_BPW] location, so we can
corrupt the memory if ->sigev_signo > _NSIG.

Btw, since you are exporting this function, may I suggest to rename it?
No, I can't suggest a better name :) But "good_sigevent" is a bit confusing
imho.

Oleg.

Re: + make-good_sigevent-non-static.patch added to -mm tree

[Sébastien Dugué]

On Fri, 26 Jan 2007 13:08:01 +0300 Oleg Nesterov <oleg@tv-sign.ru> wrote:

> On 01/26, S?bastien Dugu? wrote:
> >
> > On Thu, 25 Jan 2007 18:43:24 +0300 Oleg Nesterov <oleg@tv-sign.ru> wrote:
> > 
> > > SИbastien DuguИ wrote:
> > > >
> > > > +struct task_struct *good_sigevent(sigevent_t *event)
> > > > +{
> > > > +	struct task_struct *task = current->group_leader;
> > > > +
> > > > +	if ((event->sigev_notify & SIGEV_THREAD_ID) == SIGEV_THREAD_ID) {
> > > > +		task = find_task_by_pid(event->sigev_notify_thread_id);
> > > > +
> > > > +		if (!task || task->tgid != current->tgid)
> > > > +			return NULL;
> > > > +	} else if (event->sigev_notify == SIGEV_SIGNAL) {
> > > 
> > > No, no, we can't use "else" here,
> > > 
> > > > +		if (event->sigev_signo <= 0 || event->sigev_signo > SIGRTMAX)
> > > 
> > > because we skip the check above in SIGEV_THREAD_ID case.
> > 
> >   Right, will fix this.
> > 
> > > 
> > > This way any user can crash the kernel with a minimal effort.
> > 
> >   Well I tried, no crash, just the signal failing to be delivered.
> 
> 	sigaddset:
> 
> 		set->sig[sig / _NSIG_BPW] |= 1UL << (sig % _NSIG_BPW);
> 
> This writes to ->sig[event->sigev_signo / _NSIG_BPW] location, so we can
> corrupt the memory if ->sigev_signo > _NSIG.

  Gawd, right.

> 
> Btw, since you are exporting this function, may I suggest to rename it?
> No, I can't suggest a better name :) But "good_sigevent" is a bit confusing
> imho.

  I agree, there was a discussion concerning this a while back but nothing came
out of it and I left it as is.

  I will try to find something more suggestive.

  Thanks,

  Sébastien.