rlimits: allow setrlimit to non-current tasks
Add locking to allow setrlimit accept task parameter other than
current.
Namely, lock tasklist_lock for read and check whether the task
structure has sighand non-null. Do all the signal processing under
that lock still held.
There are some points:
1) security_task_setrlimit is now called with that lock held. This is
not new, many security_* functions are called with this lock held
already so it doesn't harm (all this security_* stuff does almost
the same).
2) task->sighand->siglock (in update_rlimit_cpu) is nested in
tasklist_lock. This dependence is already existing.
3) tsk->alloc_lock is nested in tasklist_lock. This is OK too, already
existing dependence.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
diff --git a/kernel/sys.c b/kernel/sys.c
index b5b96e3..9dbcbbc 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1272,6 +1272,7 @@
#endif
+/* make sure you are allowed to change @tsk limits before calling this */
int do_setrlimit(struct task_struct *tsk, unsigned int resource,
struct rlimit *new_rlim)
{
@@ -1285,9 +1286,16 @@
if (resource == RLIMIT_NOFILE && new_rlim->rlim_max > sysctl_nr_open)
return -EPERM;
+ /* protect tsk->signal and tsk->sighand from disappearing */
+ read_lock(&tasklist_lock);
+ if (!tsk->sighand) {
+ retval = -ESRCH;
+ goto out;
+ }
+
retval = security_task_setrlimit(tsk->group_leader, resource, new_rlim);
if (retval)
- return retval;
+ goto out;
if (resource == RLIMIT_CPU && new_rlim->rlim_cur == 0) {
/*
@@ -1322,6 +1330,7 @@
update_rlimit_cpu(tsk, new_rlim->rlim_cur);
out:
+ read_unlock(&tasklist_lock);
return retval;
}