pids: sys_getsid: fix unsafe *pid usage, fix possible 0 instead of -ESRCH
1. sys_getsid() needs rcu_read_lock() to derive the session _nr, even if
the task is current, otherwise we can race with another thread which
does sys_setsid().
2. The task can exit between find_task_by_vpid() and task_session_vnr(),
in that unlikely case sys_getsid() returns 0 instead of -ESRCH.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/sys.c b/kernel/sys.c
index 5d0b44c..ddd28e2 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1022,23 +1022,30 @@
asmlinkage long sys_getsid(pid_t pid)
{
- if (!pid)
- return task_session_vnr(current);
- else {
- int retval;
- struct task_struct *p;
+ struct task_struct *p;
+ struct pid *sid;
+ int retval;
- rcu_read_lock();
- p = find_task_by_vpid(pid);
+ rcu_read_lock();
+ if (!pid)
+ sid = task_session(current);
+ else {
retval = -ESRCH;
- if (p) {
- retval = security_task_getsid(p);
- if (!retval)
- retval = task_session_vnr(p);
- }
- rcu_read_unlock();
- return retval;
+ p = find_task_by_vpid(pid);
+ if (!p)
+ goto out;
+ sid = task_session(p);
+ if (!sid)
+ goto out;
+
+ retval = security_task_getsid(p);
+ if (retval)
+ goto out;
}
+ retval = pid_vnr(sid);
+out:
+ rcu_read_unlock();
+ return retval;
}
asmlinkage long sys_setsid(void)
