From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Lee Jones <lee@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
John Fastabend <john.fastabend@gmail.com>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH v2 1/1] bpf: Drop unprotected find_vpid() in favour of find_get_pid()
Date: Thu, 4 Aug 2022 10:16:59 -0700 [thread overview]
Message-ID: <CAADnVQ+X_B4LC6CtYM1PXPA4BBprWLj5Qip--Eeu32Zti==Ydw@mail.gmail.com> (raw)
In-Reply-To: <20220803134821.425334-1-lee@kernel.org>
On Wed, Aug 3, 2022 at 6:48 AM Lee Jones <lee@kernel.org> wrote:
>
> The documentation for find_pid() clearly states:
>
> "Must be called with the tasklist_lock or rcu_read_lock() held."
>
> Presently we do neither.
>
> Let's use find_get_pid() which searches for the vpid, then takes a
> reference to it preventing early free, all within the safety of
> rcu_read_lock(). Once we have our reference we can safely make use of
> it up until the point it is put.
>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: John Fastabend <john.fastabend@gmail.com>
> Cc: Andrii Nakryiko <andrii@kernel.org>
> Cc: Martin KaFai Lau <martin.lau@linux.dev>
> Cc: Song Liu <song@kernel.org>
> Cc: Yonghong Song <yhs@fb.com>
> Cc: KP Singh <kpsingh@kernel.org>
> Cc: Stanislav Fomichev <sdf@google.com>
> Cc: Hao Luo <haoluo@google.com>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Cc: bpf@vger.kernel.org
> Fixes: 41bdc4b40ed6f ("bpf: introduce bpf subcommand BPF_TASK_FD_QUERY")
> Signed-off-by: Lee Jones <lee@kernel.org>
> ---
>
> v1 => v2:
> * Commit log update - no code differences
>
> kernel/bpf/syscall.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 83c7136c5788d..c20cff30581c4 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -4385,6 +4385,7 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
> const struct perf_event *event;
> struct task_struct *task;
> struct file *file;
> + struct pid *ppid;
> int err;
>
> if (CHECK_ATTR(BPF_TASK_FD_QUERY))
> @@ -4396,7 +4397,9 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
> if (attr->task_fd_query.flags != 0)
> return -EINVAL;
>
> - task = get_pid_task(find_vpid(pid), PIDTYPE_PID);
> + ppid = find_get_pid(pid);
> + task = get_pid_task(ppid, PIDTYPE_PID);
> + put_pid(ppid);
rcu_read_lock/unlock around this line
would be a cheaper and faster alternative than pid's
refcount inc/dec.
next prev parent reply other threads:[~2022-08-04 17:17 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-03 13:48 [PATCH v2 1/1] bpf: Drop unprotected find_vpid() in favour of find_get_pid() Lee Jones
2022-08-03 15:27 ` Jiri Olsa
2022-08-09 6:50 ` Lee Jones
2022-08-04 17:16 ` Alexei Starovoitov [this message]
2022-08-09 6:50 ` Lee Jones
2022-08-09 14:38 ` Alexei Starovoitov
2022-08-10 11:03 ` Lee Jones
2022-08-10 11:52 ` Jiri Olsa
2022-08-10 15:09 ` Yonghong Song
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