Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/3] Revert "proc/wchan: use printk format instead of lookup_symbol_name()" | From | Helge Deller <> | Date | Fri, 24 Sep 2021 10:17:53 +0200 |
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On 9/24/21 8:20 AM, Kees Cook wrote: > This reverts commit 152c432b128cb043fc107e8f211195fe94b2159c. > > When a kernel address couldn't be symbolized for /proc/$pid/wchan, it > would leak the raw value, a potential information exposure. This is a > regression compared to the safer pre-v5.12 behavior.
Instead of reverting, another possibility might be to depend on CONFIG_KALLSYMS before using the %ps format specifier and print "0" otherwise. If it can't be symbolized it's most likely not a valid kernel address and as such wouldn't leak anything.... But well, Acked-by: Helge Deller <deller@gmx.de>
Helge
> Reported-by: kernel test robot <oliver.sang@intel.com> > Link: https://lore.kernel.org/all/20210103142726.GC30643@xsang-OptiPlex-9020/ > Reported-by: Vito Caputo <vcaputo@pengaru.com> > Link: https://lore.kernel.org/lkml/20210921193249.el476vlhg5k6lfcq@shells.gnugeneration.com/ > Reported-by: Jann Horn <jannh@google.com> > Link: https://lore.kernel.org/lkml/CAG48ez2zC=+PuNgezH53HBPZ8CXU5H=vkWx7nJs60G8RXt3w0Q@mail.gmail.com/ > Cc: stable@vger.kernel.org > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > fs/proc/base.c | 19 +++++++++++-------- > 1 file changed, 11 insertions(+), 8 deletions(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index 533d5836eb9a..1f394095eb88 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -67,6 +67,7 @@ > #include <linux/mm.h> > #include <linux/swap.h> > #include <linux/rcupdate.h> > +#include <linux/kallsyms.h> > #include <linux/stacktrace.h> > #include <linux/resource.h> > #include <linux/module.h> > @@ -386,17 +387,19 @@ static int proc_pid_wchan(struct seq_file *m, struct pid_namespace *ns, > struct pid *pid, struct task_struct *task) > { > unsigned long wchan; > + char symname[KSYM_NAME_LEN]; > > - if (ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) > - wchan = get_wchan(task); > - else > - wchan = 0; > + if (!ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS)) > + goto print0; > > - if (wchan) > - seq_printf(m, "%ps", (void *) wchan); > - else > - seq_putc(m, '0'); > + wchan = get_wchan(task); > + if (wchan && !lookup_symbol_name(wchan, symname)) { > + seq_puts(m, symname); > + return 0; > + } > > +print0: > + seq_putc(m, '0'); > return 0; > } > #endif /* CONFIG_KALLSYMS */ >
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