From: "Paul E. McKenney" paulmck@kernel.org

commit 8ed00760203d8018bee042fbfe8e076579be2c2b upstream.

Currently, cleanup_srcu_struct() checks for a grace period in progress, but it does not check for a grace period that has not yet started but which might start at any time. Such a situation could result in a use-after-free bug, so this commit adds a check for a grace period that is needed but not yet started to cleanup_srcu_struct().

Fixes: da915ad5cf25 ("srcu: Parallelize callback handling") Signed-off-by: Paul E. McKenney paulmck@kernel.org [ kovalev: backport to fix CVE-2022-49651; added Fixes tag for commit da915ad5cf25 that introduced the srcu_gp_seq_needed field and the race condition between grace period requests and cleanup ] Signed-off-by: Vasiliy Kovalev kovalev@altlinux.org --- kernel/rcu/srcutree.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index b8821665c435..5d89d941280f 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -388,9 +388,11 @@ void cleanup_srcu_struct(struct srcu_struct *ssp) return; /* Forgot srcu_barrier(), so just leak it! */ } if (WARN_ON(rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) != SRCU_STATE_IDLE) || + WARN_ON(rcu_seq_current(&ssp->srcu_gp_seq) != ssp->srcu_gp_seq_needed) || WARN_ON(srcu_readers_active(ssp))) { - pr_info("%s: Active srcu_struct %p state: %d\n", - __func__, ssp, rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq))); + pr_info("%s: Active srcu_struct %p read state: %d gp state: %lu/%lu\n", + __func__, ssp, rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)), + rcu_seq_current(&ssp->srcu_gp_seq), ssp->srcu_gp_seq_needed); return; /* Caller forgot to stop doing call_srcu()? */ } free_percpu(ssp->sda);