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SubjectRe: [PATCH 1/3] Revert "proc/wchan: use printk format instead of lookup_symbol_name()"
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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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