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.

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.gnugener... Reported-by: Jann Horn jannh@google.com Link: https://lore.kernel.org/lkml/CAG48ez2zC=+PuNgezH53HBPZ8CXU5H=vkWx7nJs60G8RXt... 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 */