[PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd

[PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd

[Zhengchao Shao]

Before detach the prog, we should check detach prog exist or not.

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
---
 samples/bpf/xdp_fwd_user.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/samples/bpf/xdp_fwd_user.c b/samples/bpf/xdp_fwd_user.c
index 1828487bae9a..a273ede3fd73 100644
--- a/samples/bpf/xdp_fwd_user.c
+++ b/samples/bpf/xdp_fwd_user.c
@@ -49,7 +49,18 @@ static int do_attach(int idx, int prog_fd, int map_fd, const char *name)
 
 static int do_detach(int idx, const char *name)
 {
-	int err;
+	int err = 1;
+	__u32 curr_prog_id;
+
+	if (bpf_xdp_query_id(idx, xdp_flags, &curr_prog_id)) {
+		printf("ERROR: bpf_xdp_query_id failed\n");
+		return err;
+	}
+
+	if (!curr_prog_id) {
+		printf("ERROR: flags(0x%x) xdp prog is not attached to %s\n", xdp_flags, name);
+		return err;
+	}
 
 	err = bpf_xdp_detach(idx, xdp_flags, NULL);
 	if (err < 0)
-- 
2.17.1

Re: [PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd

[Toke Høiland-Jørgensen]

Zhengchao Shao <shaozhengchao@huawei.com> writes:

> Before detach the prog, we should check detach prog exist or not.

If we're adding such a check we should also check that it's the *right*
program. I.e., query the ID for the program name and check that it
matches what the program attached, then obtain an fd and pass that as
XDP_EXPECTED_FD on detach to make sure it wasn't swapped out in the
meantime...

-Toke

答复: [PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd

[shaozhengchao]

-----邮件原件-----
发件人: Toke Høiland-Jørgensen [mailto:toke@kernel.org] 
发送时间: 2022年5月9日 17:46
收件人: shaozhengchao <shaozhengchao@huawei.com>; bpf@vger.kernel.org; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; ast@kernel.org; daniel@iogearbox.net; davem@davemloft.net; kuba@kernel.org; hawk@kernel.org; john.fastabend@gmail.com; andrii@kernel.org; kafai@fb.com; songliubraving@fb.com; yhs@fb.com; kpsingh@kernel.org
抄送: weiyongjun (A) <weiyongjun1@huawei.com>; shaozhengchao <shaozhengchao@huawei.com>; yuehaibing <yuehaibing@huawei.com>
主题: Re: [PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd

Zhengchao Shao <shaozhengchao@huawei.com> writes:

> Before detach the prog, we should check detach prog exist or not.

If we're adding such a check we should also check that it's the *right* program. I.e., query the ID for the program name and check that it matches what the program attached, then obtain an fd and pass that as XDP_EXPECTED_FD on detach to make sure it wasn't swapped out in the meantime...

-Toke

Thank you for your reply. When finish running xdp_fwd to attatch prog, the program will exit and can't store fd as XDP_EXPECTED_FD. 

I think the sample xdp_fwd -d is just detach prog and don't care if the fd is expected.

-zhengchao shao 

Re: 答复: [PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd

[Toke Høiland-Jørgensen]

shaozhengchao <shaozhengchao@huawei.com> writes:

> -----邮件原件-----
> 发件人: Toke Høiland-Jørgensen [mailto:toke@kernel.org] 
> 发送时间: 2022年5月9日 17:46
> 收件人: shaozhengchao <shaozhengchao@huawei.com>; bpf@vger.kernel.org; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; ast@kernel.org; daniel@iogearbox.net; davem@davemloft.net; kuba@kernel.org; hawk@kernel.org; john.fastabend@gmail.com; andrii@kernel.org; kafai@fb.com; songliubraving@fb.com; yhs@fb.com; kpsingh@kernel.org
> 抄送: weiyongjun (A) <weiyongjun1@huawei.com>; shaozhengchao <shaozhengchao@huawei.com>; yuehaibing <yuehaibing@huawei.com>
> 主题: Re: [PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd
>
> Zhengchao Shao <shaozhengchao@huawei.com> writes:
>
>> Before detach the prog, we should check detach prog exist or not.
>
> If we're adding such a check we should also check that it's the *right* program. I.e., query the ID for the program name and check that it matches what the program attached, then obtain an fd and pass that as XDP_EXPECTED_FD on detach to make sure it wasn't swapped out in the meantime...
>
> -Toke
>
> Thank you for your reply. When finish running xdp_fwd to attatch prog,
> the program will exit and can't store fd as XDP_EXPECTED_FD.
>
> I think the sample xdp_fwd -d is just detach prog and don't care if
> the fd is expected.

So why are you adding the check? Either keep it the way it is, or add a
proper check that examines the program type; you're right that it
doesn't store the prog FD, but you can still check the program name and
see if it matches to get some idea that it's not a totally separate
program that's loaded. I think doing so would be an improvement to the
sample, but just adding a check if a program is loaded is not, really...

-Toke

答复: 答复: [PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd

[shaozhengchao]

-----邮件原件-----
发件人: Toke Høiland-Jørgensen [mailto:toke@kernel.org] 
发送时间: 2022年5月9日 18:55
收件人: shaozhengchao <shaozhengchao@huawei.com>; bpf@vger.kernel.org; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; ast@kernel.org; daniel@iogearbox.net; davem@davemloft.net; kuba@kernel.org; hawk@kernel.org; john.fastabend@gmail.com; andrii@kernel.org; kafai@fb.com; songliubraving@fb.com; yhs@fb.com; kpsingh@kernel.org
抄送: weiyongjun (A) <weiyongjun1@huawei.com>; yuehaibing <yuehaibing@huawei.com>
主题: Re: 答复: [PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd

shaozhengchao <shaozhengchao@huawei.com> writes:

> -----邮件原件-----
> 发件人: Toke Høiland-Jørgensen [mailto:toke@kernel.org]
> 发送时间: 2022年5月9日 17:46
> 收件人: shaozhengchao <shaozhengchao@huawei.com>; bpf@vger.kernel.org; 
> netdev@vger.kernel.org; linux-kernel@vger.kernel.org; ast@kernel.org; 
> daniel@iogearbox.net; davem@davemloft.net; kuba@kernel.org; 
> hawk@kernel.org; john.fastabend@gmail.com; andrii@kernel.org; 
> kafai@fb.com; songliubraving@fb.com; yhs@fb.com; kpsingh@kernel.org
> 抄送: weiyongjun (A) <weiyongjun1@huawei.com>; shaozhengchao 
> <shaozhengchao@huawei.com>; yuehaibing <yuehaibing@huawei.com>
> 主题: Re: [PATCH bpf-next] samples/bpf: check detach prog exist or not 
> in xdp_fwd
>
> Zhengchao Shao <shaozhengchao@huawei.com> writes:
>
>> Before detach the prog, we should check detach prog exist or not.
>
> If we're adding such a check we should also check that it's the *right* program. I.e., query the ID for the program name and check that it matches what the program attached, then obtain an fd and pass that as XDP_EXPECTED_FD on detach to make sure it wasn't swapped out in the meantime...
>
> -Toke
>
> Thank you for your reply. When finish running xdp_fwd to attatch prog, 
> the program will exit and can't store fd as XDP_EXPECTED_FD.
>
> I think the sample xdp_fwd -d is just detach prog and don't care if 
> the fd is expected.

So why are you adding the check? Either keep it the way it is, or add a proper check that examines the program type; you're right that it doesn't store the prog FD, but you can still check the program name and see if it matches to get some idea that it's not a totally separate program that's loaded. I think doing so would be an improvement to the sample, but just adding a check if a program is loaded is not, really...

-Toke


Could I add helper function to implement this function which can check the program name and see if it attach to the device.

-Zhengchao Shao

Re: 答复: 答复: [PATCH bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd

[Toke Høiland-Jørgensen]

> Could I add helper function to implement this function which can check
> the program name and see if it attach to the device.

You just need to call bpf_prog_get_fd_by_id() followed by
bpf_obj_get_info_by_fd(), and the program name will be in info.name.
Here's an example in libxdp where we pull out the prog name:

https://github.com/xdp-project/xdp-tools/blob/master/lib/libxdp/libxdp.c#L1165

-Toke