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SubjectRe: Q: selinux_bprm_committed_creds() && signals/do_wait
Date
Oleg Nesterov <oleg@redhat.com> wrote:

> > I suspect we should pass SIGKILL
>
> Or we can fliter out SIGKILLs, yes.

How about the attached patch?

David
---
From: David Howells <dhowells@redhat.com>
Subject: [PATCH] SELinux: Don't flush inherited SIGKILL during execve()

Don't flush inherited SIGKILL during execve() in SELinux's post cred commit
hook. This isn't really a security problem: if the SIGKILL came before the
credentials were changed, then we were right to receive it at the time, and
should honour it; if it came after the creds were changed, then we definitely
should honour it; and in any case, all that will happen is that the process
will be scrapped before it ever returns to userspace.

Signed-off-by: David Howells <dhowells@redhat.com>
---

include/linux/sched.h | 1 +
kernel/signal.c | 11 ++++++++---
security/selinux/hooks.c | 11 +++++++----
3 files changed, 16 insertions(+), 7 deletions(-)


diff --git a/include/linux/sched.h b/include/linux/sched.h
index b4c38bc..3fa82b3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1885,6 +1885,7 @@ extern void sched_dead(struct task_struct *p);

extern void proc_caches_init(void);
extern void flush_signals(struct task_struct *);
+extern void __flush_signals(struct task_struct *);
extern void ignore_signals(struct task_struct *);
extern void flush_signal_handlers(struct task_struct *, int force_default);
extern int dequeue_signal(struct task_struct *tsk, sigset_t *mask, siginfo_t *info);
diff --git a/kernel/signal.c b/kernel/signal.c
index d803473..d2dd9cf 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -249,14 +249,19 @@ void flush_sigqueue(struct sigpending *queue)
/*
* Flush all pending signals for a task.
*/
+void __flush_signals(struct task_struct *t)
+{
+ clear_tsk_thread_flag(t, TIF_SIGPENDING);
+ flush_sigqueue(&t->pending);
+ flush_sigqueue(&t->signal->shared_pending);
+}
+
void flush_signals(struct task_struct *t)
{
unsigned long flags;

spin_lock_irqsave(&t->sighand->siglock, flags);
- clear_tsk_thread_flag(t, TIF_SIGPENDING);
- flush_sigqueue(&t->pending);
- flush_sigqueue(&t->signal->shared_pending);
+ __flush_signals(t);
spin_unlock_irqrestore(&t->sighand->siglock, flags);
}

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index ba808ef..b3ff7fa 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2398,11 +2398,14 @@ static void selinux_bprm_committed_creds(struct linux_binprm *bprm)
memset(&itimer, 0, sizeof itimer);
for (i = 0; i < 3; i++)
do_setitimer(i, &itimer, NULL);
- flush_signals(current);
spin_lock_irq(&current->sighand->siglock);
- flush_signal_handlers(current, 1);
- sigemptyset(&current->blocked);
- recalc_sigpending();
+ if (!sigismember(&current->pending.signal, SIGKILL) &&
+ !sigismember(&current->signal->shared_pending.signal,
+ SIGKILL)) {
+ __flush_signals(current);
+ flush_signal_handlers(current, 1);
+ sigemptyset(&current->blocked);
+ }
spin_unlock_irq(&current->sighand->siglock);
}


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