Re: [PATCH v3] fs/proc, core/debug: Don't expose absolute kernel addresses via wchan

[Andrey Ryabinin]

2015-10-01 10:57 GMT+03:00 Ingo Molnar <mingo@xxxxxxxxxx>:
> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> index d411ca63c8b6..db64f7d6492d 100644
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -140,7 +140,8 @@ Table 1-1: Process specific entries in /proc
>   stat          Process status
>   statm         Process memory status information
>   status                Process status in human readable form
> - wchan         If CONFIG_KALLSYMS is set, a pre-decoded wchan
> + wchan         If CONFIG_KALLSYMS=y, wchan (the kernel function the process is
> +               blocked in) symbol string. "0" if not blocked or !KALLSYMS.

/proc/PID/wchan is under #ifdef CONFIG_KALLSYMS.


> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index b25eee4cead5..6f05aabce3aa 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -430,13 +430,10 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns,
>
>         wchan = get_wchan(task);
>
> -       if (lookup_symbol_name(wchan, symname) < 0) {
> -               if (!ptrace_may_access(task, PTRACE_MODE_READ))
> -                       return 0;
> -               seq_printf(m, "%lu", wchan);
> -       } else {
> +       if (!lookup_symbol_name(wchan, symname))
>                 seq_printf(m, "%s", symname);
> -       }
> +       else
> +               seq_putc(m, '0');

Maybe we should respect 'kptr_restrict' sysctl when we use '%ps', '%pB' etc.
printk formats (AFAIK %ps just prints address if KALLSYMS=n, or lookup failed).
In that case you could just do 'seq_printf(m, "%ps", wchan)'.


OTOH, %ps, %pS are used mostly in debugging, so investigating some crash
in production kernel with no !KALLSYMS and with kptr_restrict != 0
will be a nightmare.
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