This is a note to let you know that I've just added the patch titled
bpf: Fix a potential use-after-free in bpf_link_free()
to the 6.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-fix-a-potential-use-after-free-in-bpf_link_free.patch
and it can be found in the queue-6.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit ddf3a5f5dd289024e4684f1950956ba3658622ca
Author: Cong Wang <cong.wang@xxxxxxxxxxxxx>
Date: Sun Jun 2 11:27:03 2024 -0700
bpf: Fix a potential use-after-free in bpf_link_free()
[ 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>
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index cb61d8880dbe0..52ffe33356418 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2985,6 +2985,7 @@ 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;
@@ -3043,16 +3044,17 @@ 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->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
@@ -3061,9 +3063,8 @@ 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)
