[PATCH RESEND v9 4/8] proc: instantiate only pids that we can ptrace on 'hidepid=4' mount option

Alexey Gladkov
2020-03-24T20:46:36Z

If "hidepid=4" mount option is set then do not instantiate pids that
we can not ptrace. "hidepid=4" means that procfs should only contain
pids that the caller can ptrace.

Cc: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Djalal Harouni <tixxdz@gmail.com>
Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com>
---
fs/proc/base.c | 15 +++++++++++++++
fs/proc/root.c | 13 ++++++++++---
include/linux/proc_fs.h | 1 +
3 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 984b97bb634b..a836979e42fe 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -701,6 +701,14 @@ static bool has_pid_permissions(struct proc_fs_info *fs_info,
struct task_struct *task,
int hide_pid_min)
{
+ /*
+ * If 'hidpid' mount option is set force a ptrace check,
+ * we indicate that we are using a filesystem syscall
+ * by passing PTRACE_MODE_READ_FSCREDS
+ */
+ if (fs_info->hide_pid == HIDEPID_NOT_PTRACEABLE)
+ return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
+
if (fs_info->hide_pid < hide_pid_min)
return true;
if (in_group_p(fs_info->pid_gid))
@@ -3319,7 +3327,14 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags)
if (!task)
goto out;

+ /* Limit procfs to only ptraceable tasks */
+ if (fs_info->hide_pid == HIDEPID_NOT_PTRACEABLE) {
+ if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS))
+ goto out_put_task;
+ }
+
result = proc_pid_instantiate(dentry, task, NULL);
+out_put_task:
put_task_struct(task);
out:
return result;
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 616e8976185c..62eae22403d2 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -47,6 +47,14 @@ static const struct fs_parameter_spec proc_fs_parameters[] = {
{}
};

+static inline int valid_hidepid(unsigned int value)
+{
+ return (value == HIDEPID_OFF ||
+ value == HIDEPID_NO_ACCESS ||
+ value == HIDEPID_INVISIBLE ||
+ value == HIDEPID_NOT_PTRACEABLE);
+}
+
static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
struct proc_fs_context *ctx = fc->fs_private;
@@ -63,10 +71,9 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param)
break;

case Opt_hidepid:
+ if (!valid_hidepid(result.uint_32))
+ return invalf(fc, "proc: unknown value of hidepid.\n");
ctx->hidepid = result.uint_32;
- if (ctx->hidepid < HIDEPID_OFF ||
- ctx->hidepid > HIDEPID_INVISIBLE)
- return invalfc(fc, "hidepid value must be between 0 and 2.\n");
break;

default:
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 7d852dbca253..21d19353fdc7 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -32,6 +32,7 @@ enum {
HIDEPID_OFF = 0,
HIDEPID_NO_ACCESS = 1,
HIDEPID_INVISIBLE = 2,
+ HIDEPID_NOT_PTRACEABLE = 4, /* Limit pids to only ptraceable pids */
};

struct proc_fs_info {
--
2.25.2