* Andrey Ryabinin <ryabinin....@gmail.com> wrote:
> 2015-10-01 10:57 GMT+03:00 Ingo Molnar <mi...@kernel.org>:
> > 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.
Yeah, indeed, so I clarified that text to now read:
+ wchan Present with CONFIG_KALLSYMS=y: it shows the kernel function
+ symbol the task is blocked in - or "0" if not blocked.
> > 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.
So this code does not use %pX, it prints the symbol. Yes, the symbol in itself
is
'information' about the execution of the task in itself - but /proc per se is
all
about providing information about tasks in the system (including to
unprivileged
users), so there's IMHO little point in restricting this output any further ...
I think ktrp_restrict is mostly about not exposing absolute addresses.
Thanks,
Ingo
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