Messages in this thread | | | Date | Thu, 1 Oct 2015 11:29:14 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v3] fs/proc, core/debug: Don't expose absolute kernel addresses via wchan |
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* Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
> 2015-10-01 10:57 GMT+03:00 Ingo Molnar <mingo@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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