bpf: Fix reference count leak in bpf_prog_test_run_xdp()

[ Upstream commit ec69daabe45256f98ac86c651b8ad1b2574489a7 ]

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 ec94670 ("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 1c19499 ("bpf: introduce frags support to
bpf_prog_test_run_xdp()") forgot to call xdp_convert_buff_to_md().

Reported-by: syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
Fixes: 1c19499 ("bpf: introduce frags support to bpf_prog_test_run_xdp()")
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/af090e53-9d9b-4412-8acb-957733b3975c@I-love.SAKURA.ne.jp
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Tetsuo Handa

net/bpf/test_run.c

@@ -1243,13 +1243,13 @@ 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++];
@@ -1261,7 +1261,7 @@ 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;
@@ -1276,6 +1276,7 @@ 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.