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authorPaul E. McKenney <paulmck@kernel.org>2020-09-15 23:27:38 +0200
committerPaul E. McKenney <paulmck@kernel.org>2020-09-17 01:32:38 +0200
commitf747c7e15d7bc71a967a94ceda686cf2460b69e8 (patch)
tree07b0f92d5e84dccbaf622e5765be228188cc13f2 /kernel
parentrcu-tasks: Fix low-probability task_struct leak (diff)
downloadlinux-f747c7e15d7bc71a967a94ceda686cf2460b69e8.tar.xz
linux-f747c7e15d7bc71a967a94ceda686cf2460b69e8.zip
rcu-tasks: Enclose task-list scan in rcu_read_lock()
The rcu_tasks_trace_postgp() function uses for_each_process_thread() to scan the task list without the benefit of RCU read-side protection, which can result in use-after-free errors on task_struct structures. This error was missed because the TRACE01 rcutorture scenario enables lockdep, but also builds with CONFIG_PREEMPT_NONE=y. In this situation, preemption is disabled everywhere, so lockdep thinks everywhere can be a legitimate RCU reader. This commit therefore adds the needed rcu_read_lock() and rcu_read_unlock(). Note that this bug can occur only after an RCU Tasks Trace CPU stall warning, which by default only happens after a grace period has extended for ten minutes (yes, not a typo, minutes). Fixes: 4593e772b502 ("rcu-tasks: Add stall warnings for RCU Tasks Trace") Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: Jiri Olsa <jolsa@redhat.com> Cc: <bpf@vger.kernel.org> Cc: <stable@vger.kernel.org> # 5.7.x Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcu/tasks.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index fcd9c25f1140..d5d9f2d03e8a 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -1088,9 +1088,11 @@ static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp)
if (ret)
break; // Count reached zero.
// Stall warning time, so make a list of the offenders.
+ rcu_read_lock();
for_each_process_thread(g, t)
if (READ_ONCE(t->trc_reader_special.b.need_qs))
trc_add_holdout(t, &holdouts);
+ rcu_read_unlock();
firstreport = true;
list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) {
if (READ_ONCE(t->trc_reader_special.b.need_qs))