Messages in this thread | | | Date | Tue, 18 Mar 2008 15:03:04 -0500 | From | serge@hallyn ... | Subject | Re: [PATCH] signals: check_kill_permission: check session under tasklist_lock |
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Quoting Oleg Nesterov (oleg@tv-sign.ru): > (on top of signals-cleanup-security_task_kill-usage-implementation.patch) > > This wasn't documented, but as Atsushi Tsuji <a-tsuji@bk.jp.nec.com> pointed > out check_kill_permission() needs tasklist_lock for task_session_nr(). > I missed this fact when removed tasklist from the callers. > > Change check_kill_permission() to take tasklist_lock for the SIGCONT case. > Re-order security checks so that we take tasklist_lock only if/when it is > actually needed. This is a minimal fix for now, tasklist will be removed > later. > > Also change the code to use task_session() instead of task_session_nr(). > > Also, remove the SIGCONT check from cap_task_kill(), it is bogus (and the > whole function is bogus. Serge, Eric, why it is still alive?). > > Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> > > --- 25/kernel/signal.c~CKP_TAKE_TASKLIST 2008-03-18 14:47:00.000000000 +0300 > +++ 25/kernel/signal.c 2008-03-18 17:25:19.000000000 +0300 > @@ -533,6 +533,7 @@ static int rm_from_queue(unsigned long m > static int check_kill_permission(int sig, struct siginfo *info, > struct task_struct *t) > { > + struct pid *sid; > int error; > > if (!valid_signal(sig)) > @@ -545,11 +546,24 @@ static int check_kill_permission(int sig > if (error) > return error; > > - if (((sig != SIGCONT) || (task_session_nr(current) != task_session_nr(t))) > - && (current->euid ^ t->suid) && (current->euid ^ t->uid) > - && (current->uid ^ t->suid) && (current->uid ^ t->uid) > - && !capable(CAP_KILL)) > - return -EPERM; > + if ((current->euid ^ t->suid) && (current->euid ^ t->uid) && > + (current->uid ^ t->suid) && (current->uid ^ t->uid) && > + !capable(CAP_KILL)) { > + switch (sig) { > + case SIGCONT: > + read_lock(&tasklist_lock); > + sid = task_session(t); > + read_unlock(&tasklist_lock); > + /* > + * We don't return the error if sid == NULL. The > + * task was unhashed, the caller must notice this. > + */ > + if (!sid || sid == task_session(current)) > + break;
Nice, in addition to a bugfix this is also far more readable.
> + default: > + return -EPERM; > + } > + } > > return security_task_kill(t, info, sig, 0); > } > --- 25/security/commoncap.c~CKP_TAKE_TASKLIST 2008-03-18 17:07:02.000000000 +0300 > +++ 25/security/commoncap.c 2008-03-18 17:21:10.000000000 +0300 > @@ -552,10 +552,6 @@ int cap_task_kill(struct task_struct *p, > if (p->uid == current->uid) > return 0; > > - /* sigcont is permitted within same session */ > - if (sig == SIGCONT && (task_session_nr(current) == task_session_nr(p))) > - return 0; > - > if (secid) > /* > * Signal sent as a particular user.
Note that cap_task_kill() should be gone anyway. What tree were you basing this on?
thanks, -serge
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