netdev - [PATCH] bpf: fix reference count leak in bpf_prog_test_run

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Message-ID: <af090e53-9d9b-4412-8acb-957733b3975c@I-love.SAKURA.ne.jp>
Date: Thu, 8 Jan 2026 21:36:48 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Alexei Starovoitov <ast@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Toke Hoiland-Jorgensen <toke@...hat.com>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>
Subject: [PATCH] bpf: fix reference count leak in bpf_prog_test_run_xdp()

syzbot is reporting

  unregister_netdevice: waiting for sit0 to become free. Usage count = 2

problem. A debug printk() patch found that a refcount is obtained at
xdp_convert_md_to_buff() from bpf_prog_test_run_xdp().

According to commit ec94670fcb3b ("bpf: Support specifying ingress via
xdp_md context in BPF_PROG_TEST_RUN"), the refcount obtained by
xdp_convert_md_to_buff() will be released by xdp_convert_buff_to_md().

Therefore, we can consider that the error handling path introduced by
commit 1c1949982524 ("bpf: introduce frags support to
bpf_prog_test_run_xdp()") forgot to call xdp_convert_buff_to_md().

Reported-by: syzbot+881d65229ca4f9ae8c84@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
Fixes: 1c1949982524 ("bpf: introduce frags support to bpf_prog_test_run_xdp()")
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
Since syzbot has no reproducer for this problem, I can't test this patch.

 net/bpf/test_run.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 655efac6f133..9a16293ba14b 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -1355,13 +1355,13 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 
 			if (sinfo->nr_frags == MAX_SKB_FRAGS) {
 				ret = -ENOMEM;
-				goto out;
+				goto out_put_dev;
 			}
 
 			page = alloc_page(GFP_KERNEL);
 			if (!page) {
 				ret = -ENOMEM;
-				goto out;
+				goto out_put_dev;
 			}
 
 			frag = &sinfo->frags[sinfo->nr_frags++];
@@ -1373,7 +1373,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 			if (copy_from_user(page_address(page), data_in + size,
 					   data_len)) {
 				ret = -EFAULT;
-				goto out;
+				goto out_put_dev;
 			}
 			sinfo->xdp_frags_size += data_len;
 			size += data_len;
@@ -1388,6 +1388,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
 		ret = bpf_test_run_xdp_live(prog, &xdp, repeat, batch_size, &duration);
 	else
 		ret = bpf_test_run(prog, &xdp, repeat, &retval, &duration, true);
+out_put_dev:
 	/* We convert the xdp_buff back to an xdp_md before checking the return
 	 * code so the reference count of any held netdevice will be decremented
 	 * even if the test run failed.
-- 
2.47.3