[PATCH RFC v3 6/7] proc: support new 'pids=all|ptraceable' mount option
From: Djalal Harouni
Date: Thu Nov 09 2017 - 11:15:23 EST
This patch introduces the new 'pids' mount option, as it was discussed
and suggested by Andy Lutomirski [1].
* If 'pids=' is passed without 'newinstance' then it has no effect.
* If 'newinstance,pids=all' then all processes will be shown in proc.
* If 'newinstance,pids=ptraceable' then only ptraceable processes will be
shown.
* 'pids=' takes precendence over 'hidepid=' since 'hidepid=' can be
ignored if "gid=" was set and caller has the "gid=" set in its groups.
We want to guarantee that LSM have a security path there that can not
be disabled with "gid=".
This allows to support lightweight sandboxes in Embedded Linux.
Later Yama LSM can be updated to check that processes are able only
able to see their children inside /proc/, allowing to support more tight
cases.
[1] https://lkml.org/lkml/2017/4/26/646
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Suggested-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Alexey Gladkov <gladkov.alexey@xxxxxxxxx>
Signed-off-by: Djalal Harouni <tixxdz@xxxxxxxxx>
---
fs/proc/base.c | 36 +++++++++++++++++++++++++++++-------
fs/proc/inode.c | 6 +++++-
fs/proc/root.c | 20 ++++++++++++++++++--
include/linux/proc_fs.h | 30 ++++++++++++++++++++++++++++++
4 files changed, 82 insertions(+), 10 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 54b527c..88b92bc 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -686,13 +686,24 @@ static bool has_pid_permissions(struct proc_fs_info *fs_info,
struct task_struct *task,
int hide_pid_min)
{
- int hide_pid = proc_fs_hide_pid(fs_info);
- kgid_t gid = proc_fs_pid_gid(fs_info);
+ int pids = proc_fs_pids(fs_info);
+
+ /*
+ * If 'pids=all' or if it was not set then lets fallback
+ * to 'hidepid' and 'gid', if those are not enforced too, then
+ * ptrace checks are skipped. Otherwise ptrace permission is
+ * required for all other cases.
+ */
+ if (pids == PIDS_ALL) {
+ int hide_pid = proc_fs_hide_pid(fs_info);
+ kgid_t gid = proc_fs_pid_gid(fs_info);
+
+ if (hide_pid < hide_pid_min)
+ return true;
- if (hide_pid < hide_pid_min)
- return true;
- if (in_group_p(gid))
- return true;
+ if (in_group_p(gid))
+ return true;
+ }
return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
}
@@ -701,6 +712,7 @@ static int proc_pid_permission(struct inode *inode, int mask)
{
struct proc_fs_info *fs_info = proc_sb(inode->i_sb);
int hide_pid = proc_fs_hide_pid(fs_info);
+ int pids = proc_fs_pids(fs_info);
struct task_struct *task;
bool has_perms;
@@ -711,7 +723,8 @@ static int proc_pid_permission(struct inode *inode, int mask)
put_task_struct(task);
if (!has_perms) {
- if (hide_pid == HIDEPID_INVISIBLE) {
+ if (pids == PIDS_PTRACEABLE ||
+ hide_pid == HIDEPID_INVISIBLE) {
/*
* Let's make getdents(), stat(), and open()
* consistent with each other. If a process
@@ -3140,6 +3153,7 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, unsign
unsigned tgid;
struct proc_fs_info *fs_info = proc_sb(dir->i_sb);
struct pid_namespace *ns = fs_info->pid_ns;
+ int pids = proc_fs_pids(fs_info);
tgid = name_to_int(&dentry->d_name);
if (tgid == ~0U)
@@ -3153,7 +3167,15 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, unsign
if (!task)
goto out;
+ /* Limit procfs to only ptraceable tasks */
+ if (pids != PIDS_ALL) {
+ cond_resched();
+ if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS))
+ goto out_put_task;
+ }
+
result = proc_pid_instantiate(dir, dentry, task, NULL);
+out_put_task:
put_task_struct(task);
out:
return ERR_PTR(result);
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index faec32a..2707d5f 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -108,8 +108,12 @@ static int proc_show_options(struct seq_file *seq, struct dentry *root)
int hide_pid = proc_fs_hide_pid(fs_info);
kgid_t pid_gid = proc_fs_pid_gid(fs_info);
- if (proc_fs_newinstance(fs_info))
+ if (proc_fs_newinstance(fs_info)) {
+ int pids = proc_fs_pids(fs_info);
+
seq_printf(seq, ",newinstance");
+ seq_printf(seq, ",pids=%s", pids == PIDS_ALL ? "all" : "ptraceable");
+ }
if (!gid_eq(pid_gid, GLOBAL_ROOT_GID))
seq_printf(seq, ",gid=%u", from_kgid_munged(current_user_ns(),pid_gid));
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 33ab965..5cdff69 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -28,13 +28,14 @@
#include "internal.h"
enum {
- Opt_gid, Opt_hidepid, Opt_newinstance, Opt_err,
+ Opt_gid, Opt_hidepid, Opt_newinstance, Opt_pids, Opt_err,
};
static const match_table_t tokens = {
{Opt_hidepid, "hidepid=%u"},
{Opt_gid, "gid=%u"},
{Opt_newinstance, "newinstance"},
+ {Opt_pids, "pids=%s"},
{Opt_err, NULL},
};
@@ -67,6 +68,7 @@ int proc_parse_early_options(char *options, struct proc_fs_info *fs_info)
break;
case Opt_gid:
case Opt_hidepid:
+ case Opt_pids:
break;
default:
pr_err("proc: unrecognized mount option \"%s\" "
@@ -83,7 +85,7 @@ int proc_parse_options(char *options, struct proc_fs_info *fs_info)
{
char *p;
substring_t args[MAX_OPT_ARGS];
- int option;
+ int option, ret = 0;
kgid_t gid;
if (!options)
@@ -119,6 +121,19 @@ int proc_parse_options(char *options, struct proc_fs_info *fs_info)
break;
case Opt_newinstance:
break;
+ case Opt_pids:
+ if (strcmp(args[0].from, "all") == 0)
+ ret = proc_fs_set_pids(fs_info, PIDS_ALL);
+ else if (strcmp(args[0].from, "ptraceable") == 0)
+ ret = proc_fs_set_pids(fs_info, PIDS_PTRACEABLE);
+ else
+ ret = -EINVAL;
+
+ if (ret < 0) {
+ pr_err("proc: invalid 'pids' mount option.\n");
+ return 0;
+ }
+ break;
default:
pr_err("proc: unrecognized mount option \"%s\" "
"or missing value\n", p);
@@ -188,6 +203,7 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
/* Set it as early as possible */
proc_fs_set_newinstance(fs_info, false);
+ proc_fs_set_pids(fs_info, PIDS_ALL);
if (flags & SB_KERNMOUNT) {
ns = data;
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index c123e5ec..0730f52 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -18,6 +18,11 @@ enum { /* definitions for 'hidepid' mount option */
HIDEPID_INVISIBLE = 2,
};
+enum { /* definitions for 'pids' mount option */
+ PIDS_ALL = 0,
+ PIDS_PTRACEABLE = 1,
+};
+
struct proc_fs_info {
struct pid_namespace *pid_ns;
struct dentry *proc_self; /* For /proc/self/ */
@@ -25,6 +30,7 @@ struct proc_fs_info {
bool newinstance; /* Flag for new separated instances */
kgid_t pid_gid;
int hide_pid;
+ int pids;
};
#ifdef CONFIG_PROC_FS
@@ -49,6 +55,16 @@ static inline void proc_fs_set_newinstance(struct proc_fs_info *fs_info, bool va
fs_info->newinstance = value;
}
+static inline int proc_fs_set_pids(struct proc_fs_info *fs_info, int value)
+{
+ if (value != PIDS_ALL &&
+ (value != PIDS_PTRACEABLE || !fs_info->newinstance))
+ return -EINVAL;
+
+ fs_info->pids = value;
+ return 0;
+}
+
static inline int proc_fs_hide_pid(struct proc_fs_info *fs_info)
{
return fs_info->hide_pid;
@@ -64,6 +80,11 @@ static inline bool proc_fs_newinstance(struct proc_fs_info *fs_info)
return fs_info->newinstance;
}
+static inline int proc_fs_pids(struct proc_fs_info *fs_info)
+{
+ return fs_info->pids;
+}
+
extern void proc_root_init(void);
extern void proc_flush_task(struct task_struct *);
@@ -112,6 +133,10 @@ static inline void proc_fs_set_newinstance(struct proc_fs_info *fs_info, bool va
{
}
+static inline int proc_fs_set_pids(struct proc_fs_info *fs_info, int value)
+{
+}
+
static inline int proc_fs_hide_pid(struct proc_fs_info *fs_info)
{
return 0;
@@ -127,6 +152,11 @@ static inline bool proc_fs_newinstance(struct proc_fs_info *fs_info)
return false;
}
+static inline int proc_fs_pids(struct proc_fs_info *fs_info)
+{
+ return 0;
+}
+
extern inline struct proc_fs_info *proc_sb(struct super_block *sb) { return NULL;}
static inline struct proc_dir_entry *proc_symlink(const char *name,
struct proc_dir_entry *parent,const char *dest) { return NULL;}
--
2.7.4