From: Cong Wang <cong.wang@xxxxxxxxxxxxx>
After commit 1a80dbcb2dba, bpf_link can be freed by
link->ops->dealloc_deferred, but the code still tests and uses
link->ops->dealloc afterward, which leads to a use-after-free as
reported by syzbot. Actually, one of them should be sufficient, so
just call one of them instead of both. Also add a WARN_ON() in case
of any problematic implementation.
Reported-by: syzbot+1989ee16d94720836244@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 1a80dbcb2dba ("bpf: support deferring bpf_link dealloc to after RCU grace period")
Cc: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx>
---
kernel/bpf/syscall.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 2222c3ff88e7..d8f244069495 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2998,6 +2998,7 @@ static int bpf_obj_get(const union bpf_attr *attr)
void bpf_link_init(struct bpf_link *link, enum bpf_link_type type,
const struct bpf_link_ops *ops, struct bpf_prog *prog)
{
+ WARN_ON(ops->dealloc && ops->dealloc_deferred);
atomic64_set(&link->refcnt, 1);
link->type = type;
link->id = 0;
@@ -3074,8 +3075,7 @@ static void bpf_link_free(struct bpf_link *link)
call_rcu_tasks_trace(&link->rcu, bpf_link_defer_dealloc_mult_rcu_gp);
else
call_rcu(&link->rcu, bpf_link_defer_dealloc_rcu_gp);
- }
- if (link->ops->dealloc)
+ } else if (link->ops->dealloc)
link->ops->dealloc(link);
}
--
2.34.1
