6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Cong Wang <cong.wang@xxxxxxxxxxxxx>
[ Upstream commit 2884dc7d08d98a89d8d65121524bb7533183a63a ]
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.
Fixes: 1a80dbcb2dba ("bpf: support deferring bpf_link dealloc to after RCU grace period")
Reported-by: syzbot+1989ee16d94720836244@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/20240602182703.207276-1-xiyou.wangcong@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
kernel/bpf/syscall.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e9a68c6043ce5..65df92f5b1922 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2830,6 +2830,7 @@ 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;
@@ -2888,16 +2889,17 @@ static void bpf_link_defer_dealloc_mult_rcu_gp(struct rcu_head *rcu)
/* bpf_link_free is guaranteed to be called from process context */
static void bpf_link_free(struct bpf_link *link)
{
+ const struct bpf_link_ops *ops = link->ops;
bool sleepable = false;
bpf_link_free_id(link->id);
if (link->prog) {
sleepable = link->prog->aux->sleepable;
/* detach BPF program, clean up used resources */
- link->ops->release(link);
+ ops->release(link);
bpf_prog_put(link->prog);
}
- if (link->ops->dealloc_deferred) {
+ if (ops->dealloc_deferred) {
/* schedule BPF link deallocation; if underlying BPF program
* is sleepable, we need to first wait for RCU tasks trace
* sync, then go through "classic" RCU grace period
@@ -2906,9 +2908,8 @@ 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)
- link->ops->dealloc(link);
+ } else if (ops->dealloc)
+ ops->dealloc(link);
}
static void bpf_link_put_deferred(struct work_struct *work)
--
2.43.0
