Re: [PATCH v2 1/1] bpf: Drop unprotected find_vpid() in favour of find_get_pid()

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Aug 03, 2022 at 02:48:21PM +0100, Lee Jones wrote:
> The documentation for find_pid() clearly states:

nit: typo find_vpid

> 
>   "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>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> ---
> 
> 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);
>  	if (!task)
>  		return -ENOENT;
>  
> -- 
> 2.37.1.455.g008518b4e5-goog
>