| Message ID | 20170109181225.GB8972@redhat.com (mailing list archive) |
|---|---|
| State | Rejected |
| Headers | show |
Seriously, could someone explain why do we need the security_task_wait() hook at all? On 01/09, Oleg Nesterov wrote: > > On 01/09, yangshukui wrote: > > > > --- a/security/selinux/hooks.c > > +++ b/security/selinux/hooks.c > > @@ -3596,6 +3596,9 @@ static int selinux_task_kill(struct task_struct *p, > > struct siginfo *info, > > > > static int selinux_task_wait(struct task_struct *p) > > { > > + if (pid_vnr(task_tgid(current)) == 1){ > > + return 0; > > this check is not really correct, it can be a sub-thread... Doesn't matter, > please see below. > > > + } > > return task_has_perm(p, current, PROCESS__SIGCHLD); > > } > > It work but it permit pid 1 process to reap child without selinux check. Can > > we have a better way to handle this problem? > > I never understood why security_task_wait() should deny to reap a child. But > since it can we probably want some explicit "the whole namespace goes away" check. > We could use, say, PIDNS_HASH_ADDING but I'd suggest something like a trivial change > below for now. > > Eric, what do you think? > > Oleg. > > diff --git a/security/security.c b/security/security.c > index f825304..1330b4e 100644 > --- a/security/security.c > +++ b/security/security.c > @@ -1027,6 +1027,9 @@ int security_task_kill(struct task_struct *p, struct siginfo *info, > > int security_task_wait(struct task_struct *p) > { > + /* must be the exiting child reaper */ > + if (unlikely(current->flags & PF_EXITING)) > + return 0; > return call_int_hook(task_wait, 0, p); > } >
On Mon, 2017-01-09 at 19:29 +0100, Oleg Nesterov wrote: > Seriously, could someone explain why do we need the > security_task_wait() > hook at all? I would be ok with killing it. IIRC, the original motivation was to block an unauthorized data flow from child to parent when the child context differs, but part of that original design was also to reparent the child automatically, and that was never implemented. I don't think there is a real use case for it in practice and it just breaks things, so let's get rid of it unless someone objects. > > > On 01/09, Oleg Nesterov wrote: > > > > > > On 01/09, yangshukui wrote: > > > > > > > > > --- a/security/selinux/hooks.c > > > +++ b/security/selinux/hooks.c > > > @@ -3596,6 +3596,9 @@ static int selinux_task_kill(struct > > > task_struct *p, > > > struct siginfo *info, > > > > > > static int selinux_task_wait(struct task_struct *p) > > > { > > > + if (pid_vnr(task_tgid(current)) == 1){ > > > + return 0; > > > > this check is not really correct, it can be a sub-thread... Doesn't > > matter, > > please see below. > > > > > > > > + } > > > return task_has_perm(p, current, PROCESS__SIGCHLD); > > > } > > > It work but it permit pid 1 process to reap child without selinux > > > check. Can > > > we have a better way to handle this problem? > > > > I never understood why security_task_wait() should deny to reap a > > child. But > > since it can we probably want some explicit "the whole namespace > > goes away" check. > > We could use, say, PIDNS_HASH_ADDING but I'd suggest something like > > a trivial change > > below for now. > > > > Eric, what do you think? > > > > Oleg. > > > > diff --git a/security/security.c b/security/security.c > > index f825304..1330b4e 100644 > > --- a/security/security.c > > +++ b/security/security.c > > @@ -1027,6 +1027,9 @@ int security_task_kill(struct task_struct *p, > > struct siginfo *info, > > > > int security_task_wait(struct task_struct *p) > > { > > + /* must be the exiting child reaper */ > > + if (unlikely(current->flags & PF_EXITING)) > > + return 0; > > return call_int_hook(task_wait, 0, p); > > } > >
On Mon, Jan 9, 2017 at 1:43 PM, Stephen Smalley <sds@tycho.nsa.gov> wrote: > On Mon, 2017-01-09 at 19:29 +0100, Oleg Nesterov wrote: >> Seriously, could someone explain why do we need the >> security_task_wait() >> hook at all? > > I would be ok with killing it. > IIRC, the original motivation was to block an unauthorized data flow > from child to parent when the child context differs, but part of that > original design was also to reparent the child automatically, and that > was never implemented. I don't think there is a real use case for it > in practice and it just breaks things, so let's get rid of it unless > someone objects. Patches are always welcome, plenty of time to get things in for 4.11 :)
On 1/9/2017 10:43 AM, Stephen Smalley wrote: > On Mon, 2017-01-09 at 19:29 +0100, Oleg Nesterov wrote: >> Seriously, could someone explain why do we need the >> security_task_wait() >> hook at all? > I would be ok with killing it. > IIRC, the original motivation was to block an unauthorized data flow > from child to parent when the child context differs, but part of that > original design was also to reparent the child automatically, and that > was never implemented. I don't think there is a real use case for it > in practice and it just breaks things, so let's get rid of it unless > someone objects. A strict Bell & LaPadula sensitivity model must prohibit a child with a more sensitive label from signalling its parent. Except that Bad Things happen when you try enforcing that on a real system. I agree with Stephen and Oleg that this hook could go away and not be missed. If someone *really* wants to implement a strict B&L policy I believe that a reparentting solution is going to be necessary anyway. Regardless of the outcome, I notice that the Smack hook does not do anything, and that's unnecessary overhead, so it's going to come out. > >> >> On 01/09, Oleg Nesterov wrote: >>> >>> On 01/09, yangshukui wrote: >>>> >>>> --- a/security/selinux/hooks.c >>>> +++ b/security/selinux/hooks.c >>>> @@ -3596,6 +3596,9 @@ static int selinux_task_kill(struct >>>> task_struct *p, >>>> struct siginfo *info, >>>> >>>> static int selinux_task_wait(struct task_struct *p) >>>> { >>>> + if (pid_vnr(task_tgid(current)) == 1){ >>>> + return 0; >>> this check is not really correct, it can be a sub-thread... Doesn't >>> matter, >>> please see below. >>> >>>> + } >>>> return task_has_perm(p, current, PROCESS__SIGCHLD); >>>> } >>>> It work but it permit pid 1 process to reap child without selinux >>>> check. Can >>>> we have a better way to handle this problem? >>> I never understood why security_task_wait() should deny to reap a >>> child. But >>> since it can we probably want some explicit "the whole namespace >>> goes away" check. >>> We could use, say, PIDNS_HASH_ADDING but I'd suggest something like >>> a trivial change >>> below for now. >>> >>> Eric, what do you think? >>> >>> Oleg. >>> >>> diff --git a/security/security.c b/security/security.c >>> index f825304..1330b4e 100644 >>> --- a/security/security.c >>> +++ b/security/security.c >>> @@ -1027,6 +1027,9 @@ int security_task_kill(struct task_struct *p, >>> struct siginfo *info, >>> >>> int security_task_wait(struct task_struct *p) >>> { >>> + /* must be the exiting child reaper */ >>> + if (unlikely(current->flags & PF_EXITING)) >>> + return 0; >>> return call_int_hook(task_wait, 0, p); >>> } >>> > -- > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
diff --git a/security/security.c b/security/security.c index f825304..1330b4e 100644 --- a/security/security.c +++ b/security/security.c @@ -1027,6 +1027,9 @@ int security_task_kill(struct task_struct *p, struct siginfo *info, int security_task_wait(struct task_struct *p) { + /* must be the exiting child reaper */ + if (unlikely(current->flags & PF_EXITING)) + return 0; return call_int_hook(task_wait, 0, p); }