From: Yonghong Song <yhs@meta.com>
To: Hou Tao <houtao@huaweicloud.com>, bpf@vger.kernel.org
Cc: Martin KaFai Lau <martin.lau@linux.dev>,
Andrii Nakryiko <andrii@kernel.org>, Song Liu <song@kernel.org>,
Hao Luo <haoluo@google.com>, Yonghong Song <yhs@fb.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Jiri Olsa <jolsa@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
houtao1@huawei.com
Subject: Re: [PATCH bpf-next v3] bpf: Pass map file to .map_update_batch directly
Date: Wed, 16 Nov 2022 15:41:06 -0800 [thread overview]
Message-ID: <48f7e9dd-b9d2-373d-6e71-c2ec17d53d73@meta.com> (raw)
In-Reply-To: <20221116075059.1551277-1-houtao@huaweicloud.com>
On 11/15/22 11:50 PM, Hou Tao wrote:
> From: Hou Tao <houtao1@huawei.com>
>
> Currently bpf_map_do_batch() first invokes fdget(batch.map_fd) to get
> the target map file, then it invokes generic_map_update_batch() to do
> batch update. generic_map_update_batch() will get the target map file
> by using fdget(batch.map_fd) again and pass it to
> bpf_map_update_value().
>
> The problem is map file returned by the second fdget() may be NULL or a
> totally different file compared by map file in bpf_map_do_batch(). The
> reason is that the first fdget() only guarantees the liveness of struct
> file instead of file descriptor and the file description may be released
> by concurrent close() through pick_file().
>
> It doesn't incur any problem as for now, because maps with batch update
> support don't use map file in .map_fd_get_ptr() ops. But it is better to
> fix the potential access of an invalid map file.
>
> Using __bpf_map_get() again in generic_map_update_batch() can not fix
> the problem, because batch.map_fd may be closed and reopened, and the
> returned map file may be different with map file got in
> bpf_map_do_batch(), so just passing the map file directly to
> .map_update_batch() in bpf_map_do_batch().
>
> Signed-off-by: Hou Tao <houtao1@huawei.com>
Acked-by: Yonghong Song <yhs@fb.com>
next prev parent reply other threads:[~2022-11-16 23:42 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-16 7:50 [PATCH bpf-next v3] bpf: Pass map file to .map_update_batch directly Hou Tao
2022-11-16 23:41 ` Yonghong Song [this message]
2022-11-17 16:20 ` patchwork-bot+netdevbpf
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