Add exec_id to signal_struct and compare it at a few choice moments.
I believe this closes the security holes that letting the zombie
threads linger after exec opens up.
The problem is that old threads may have different creds after a setuid
exec, and then formerly shared resources may change. So signal sending
and accesses by proc need to be blocked.
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
---
fs/exec.c | 1 +
include/linux/sched/signal.h | 1 +
kernel/fork.c | 1 +
kernel/ptrace.c | 4 ++++
kernel/signal.c | 7 ++++++-
5 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/fs/exec.c b/fs/exec.c
index 303a114b00ce..730dee8bb2f8 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1323,6 +1323,7 @@ void setup_new_exec(struct linux_binprm * bprm)
/* An exec changes our domain. We are no longer part of the thread
group */
current->self_exec_id++;
+ current->signal->exec_id = current->self_exec_id;
flush_signal_handlers(current, 0);
}
EXPORT_SYMBOL(setup_new_exec);
diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index 2cf446704cd4..63ae951ee330 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -80,6 +80,7 @@ struct signal_struct {
atomic_t live;
int nr_threads;
struct list_head thread_head;
+ u32 exec_id;
wait_queue_head_t wait_chldexit; /* for wait4() */
diff --git a/kernel/fork.c b/kernel/fork.c
index 0632ac1180be..a442fa099842 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1387,6 +1387,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
sig->oom_score_adj = current->signal->oom_score_adj;
sig->oom_score_adj_min = current->signal->oom_score_adj_min;
+ sig->exec_id = current->self_exec_id;
mutex_init(&sig->cred_guard_mutex);
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 0af928712174..cc6b10b1ffbe 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -277,6 +277,10 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
* or halting the specified task is impossible.
*/
+ /* Don't allow inspecting a thread after exec */
+ if (task->self_exec_id != task->signal->exec_id)
+ return 1;
+
/* Don't let security modules deny introspection */
if (same_thread_group(task, current))
return 0;
diff --git a/kernel/signal.c b/kernel/signal.c
index fd75ba33ee3d..fe8dcdb622f5 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -995,6 +995,10 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
from_ancestor_ns || (info == SEND_SIG_FORCED)))
goto ret;
+ /* Don't allow thread group signals after exec */
+ if (group && (t->signal->exec_id != t->self_exec_id))
+ goto ret;
+
pending = group ? &t->signal->shared_pending : &t->pending;
/*
* Short-circuit ignored signals and support queuing
@@ -1247,7 +1251,8 @@ struct sighand_struct *__lock_task_sighand(struct task_struct *tsk,
* must see ->sighand == NULL.
*/
spin_lock(&sighand->siglock);
- if (likely(sighand == tsk->sighand)) {
+ if (likely((sighand == tsk->sighand) &&
+ (tsk->self_exec_id == tsk->signal->exec_id))) {
rcu_read_unlock();
break;
}
--
2.10.1
--
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