[RFC] procfs: add hidepid and hidenet modes

From: Vasiliy Kulikov
Date: Sun Jun 12 2011 - 03:54:32 EST

This patch introduces support of procfs mount options and adds mount
options to restrict access to /proc/PID/ directories and /proc/PID/net/
contents. The default backward-compatible behaviour is left untouched.

The first mount option is called "hidepid" and its value defines how much
info about processes we want to be available for non-owners:

hidepid=0 (default) means the current behaviour - anybody may read all
world-readable /proc/PID/* files.

hidepid=1 means users may not access any /proc/<pid>/ directories, but their
own. Sensitive files like cmdline, io, sched*, status, wchan are now
protected against other users. As permission checking done in
proc_pid_permission() and files' permissions are left untouched,
programs expecting specific files' permissions are not confused.

hidepid=2 means hidepid=1 plus all /proc/PID/ will be invisible to
other users. It doesn't mean that it hides a fact whether a process
exists (it can be learned by other means, e.g. by sending signals), but
it hides process' euid and egid. It greatly compicates intruder's task of
gathering info about running processes, whether some daemon runs with
elevated privileges, whether other user runs some sensitive program,
whether other users run any program at all, etc.

hidenet means /proc/PID/net will be accessible to processes with
CAP_NET_ADMIN capability or to members of a special group.

gid=XXX defines a group that will be able to gather all processes' info
and network connections info.

Similar features are implemented for old kernels in -ow patches (for
Linux 2.2 and 2.4) and for Linux 2.6 in -grsecurity (but both of them
are implemented as configure options, not cofigurable in runtime).


In current version hidenet works for CONFIG_NET_NS=y via creating a
"fake" net namespace and slipping it to nonauthorized users, resulting
in users observing blank net files (like nobody use the network). If
CONFIG_NET_NS=n I don't see anything better than just fully denying
access to /proc/<pid>/net. More elegant ideas are welcome.

Signed-off-by: Vasiliy Kulikov <segoon@xxxxxxxxxxxx>
--
Documentation/filesystems/proc.txt | 51 ++++++++++++++++++++++
fs/proc/base.c | 62 ++++++++++++++++++++++++++-
fs/proc/inode.c | 20 +++++++++
fs/proc/internal.h | 1 +
fs/proc/proc_net.c | 26 +++++++++++
fs/proc/root.c | 83 +++++++++++++++++++++++++++++++++++-
include/linux/pid_namespace.h | 3 +
include/net/net_namespace.h | 2 +
net/core/net_namespace.c | 2 +-
9 files changed, 246 insertions(+), 4 deletions(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 23cae65..4fd35c4 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -41,6 +41,8 @@ Table of Contents
3.5 /proc/<pid>/mountinfo - Information about mounts
3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm

+ 4 Configuring procfs
+ 4.1 Mount options

------------------------------------------------------------------------------
Preface
@@ -1535,3 +1537,52 @@ a task to set its own or one of its thread siblings comm value. The comm value
is limited in size compared to the cmdline value, so writing anything longer
then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
comm value.
+
+
+------------------------------------------------------------------------------
+Configuring procfs
+------------------------------------------------------------------------------
+
+4.1 Mount options
+---------------------
+
+The following mount options are supported:
+
+ hidepid= Set /proc/<pid>/ access mode.
+ hidenet Hide /proc/<pid>/net/ from nonauthorized users.
+ nohidenet Don't hide /proc/<pid>/net/ from nonauthorized users.
+ gid= Set the group authorized to learn processes and
+ networking information.
+
+hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
+(default).
+
+hidepid=1 means users may not access any /proc/<pid>/ directories, but their
+own. Sensitive files like cmdline, io, sched*, status, wchan are now protected
+against other users. This makes impossible to learn whether any user runs
+specific program (given the program doesn't reveal itself by its behaviour).
+As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
+poorly written programs passing sensitive information via program arguments are
+now protected against local eavesdroppers.
+
+hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
+users. It doesn't mean that it hides a fact whether a process with a specific
+pid value exists (it can be learned by other means, e.g. by sending signals),
+but it hides process' euid and egid, which may be learned by stat()'ing
+/proc/<pid>/ otherwise. It greatly complicates intruder's task of gathering info
+about running processes, whether some daemon runs with elevated privileges,
+whether other user runs some sensitive program, whether other users run any
+program at all, etc.
+
+hidenet means /proc/<pid>/net/ will be accessible to processes with
+CAP_NET_ADMIN capability or to members of a special group. It means
+nonauthorized users may not learn any networking connections information. If
+network namespaces support is enabled (CONFIG_NET_NS=y) then common users would
+obtain net directory, but all files would indicate no networking activity at
+all. If network namespaces are disabled, net directory is unaccessible to
+common users.
+
+gid= means group authorized to learn processes information prohibited by
+hidepid= and networking information prohibited by hidenet. If you use some
+daemon like identd which have to learn information about net/processes
+information, just add identd to this group.
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9d096e8..ff2feee 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -568,8 +568,40 @@ static int proc_setattr(struct dentry *dentry, struct iattr *attr)
return 0;
}

+static int proc_pid_permission(struct inode *inode, int mask,
+ unsigned int flags)
+{
+ struct pid_namespace *pid = inode->i_sb->s_fs_info;
+ struct task_struct *task = get_proc_task(inode);
+
+ if (pid->hide_pid &&
+ !ptrace_may_access(task, PTRACE_MODE_READ) &&
+ !in_group_p(pid->pid_gid)) {
+ if (pid->hide_pid == 2)
+ return -ENOENT;
+ else
+ return -EPERM;
+ }
+ return generic_permission(inode, mask, flags, NULL);
+}
+
+/*
+ * May current process learn task's euid/egid?
+ */
+static bool proc_pid_may_getattr(struct pid_namespace *pid,
+ struct task_struct *task)
+{
+ if (pid->hide_pid < 2)
+ return true;
+ if (ptrace_may_access(task, PTRACE_MODE_READ))
+ return true;
+ return in_group_p(pid->pid_gid);
+}
+
+
static const struct inode_operations proc_def_inode_operations = {
.setattr = proc_setattr,
+ .permission = proc_pid_permission,
};

static int mounts_open_common(struct inode *inode, struct file *file,
@@ -1662,6 +1694,7 @@ static const struct inode_operations proc_pid_link_inode_operations = {
.readlink = proc_pid_readlink,
.follow_link = proc_pid_follow_link,
.setattr = proc_setattr,
+ .permission = proc_pid_permission,
};


@@ -1730,6 +1763,7 @@ static int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat
struct inode *inode = dentry->d_inode;
struct task_struct *task;
const struct cred *cred;
+ struct pid_namespace *pid = dentry->d_sb->s_fs_info;

generic_fillattr(inode, stat);

@@ -1738,6 +1772,14 @@ static int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat
stat->gid = 0;
task = pid_task(proc_pid(inode), PIDTYPE_PID);
if (task) {
+ if (!proc_pid_may_getattr(pid, task)) {
+ rcu_read_unlock();
+ /*
+ * This doesn't prevent learning whether PID exists,
+ * it only makes getattr() consistent with readdir().
+ */
+ return -ENOENT;
+ }
if ((inode->i_mode == (S_IFDIR|S_IRUGO|S_IXUGO)) ||
task_dumpable(task)) {
cred = __task_cred(task);
@@ -2184,6 +2226,7 @@ static const struct inode_operations proc_fd_inode_operations = {
.lookup = proc_lookupfd,
.permission = proc_fd_permission,
.setattr = proc_setattr,
+ .permission = proc_pid_permission,
};

static struct dentry *proc_fdinfo_instantiate(struct inode *dir,
@@ -2236,6 +2279,7 @@ static const struct file_operations proc_fdinfo_operations = {
static const struct inode_operations proc_fdinfo_inode_operations = {
.lookup = proc_lookupfdinfo,
.setattr = proc_setattr,
+ .permission = proc_pid_permission,
};


@@ -2473,6 +2517,7 @@ static const struct inode_operations proc_attr_dir_inode_operations = {
.lookup = proc_attr_dir_lookup,
.getattr = pid_getattr,
.setattr = proc_setattr,
+ .permission = proc_pid_permission,
};

#endif
@@ -2890,6 +2935,7 @@ static const struct inode_operations proc_tgid_base_inode_operations = {
.lookup = proc_tgid_base_lookup,
.getattr = pid_getattr,
.setattr = proc_setattr,
+ .permission = proc_pid_permission,
};

static void proc_flush_task_mnt(struct vfsmount *mnt, pid_t pid, pid_t tgid)
@@ -3093,6 +3139,12 @@ static int proc_pid_fill_cache(struct file *filp, void *dirent, filldir_t filldi
proc_pid_instantiate, iter.task, NULL);
}

+static int fake_filldir(void *buf, const char *name, int namelen,
+ loff_t offset, u64 ino, unsigned d_type)
+{
+ return 0;
+}
+
/* for the /proc/ directory itself, after non-process stuff has been done */
int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
@@ -3100,6 +3152,7 @@ int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
struct task_struct *reaper = get_proc_task(filp->f_path.dentry->d_inode);
struct tgid_iter iter;
struct pid_namespace *ns;
+ filldir_t __filldir;

if (!reaper)
goto out_no_task;
@@ -3116,8 +3169,13 @@ int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
for (iter = next_tgid(ns, iter);
iter.task;
iter.tgid += 1, iter = next_tgid(ns, iter)) {
+ if (proc_pid_may_getattr(ns, iter.task))
+ __filldir = filldir;
+ else
+ __filldir = fake_filldir;
+
filp->f_pos = iter.tgid + TGID_OFFSET;
- if (proc_pid_fill_cache(filp, dirent, filldir, iter) < 0) {
+ if (proc_pid_fill_cache(filp, dirent, __filldir, iter) < 0) {
put_task_struct(iter.task);
goto out;
}
@@ -3223,6 +3281,7 @@ static const struct inode_operations proc_tid_base_inode_operations = {
.lookup = proc_tid_base_lookup,
.getattr = pid_getattr,
.setattr = proc_setattr,
+ .permission = proc_pid_permission,
};

static struct dentry *proc_task_instantiate(struct inode *dir,
@@ -3448,6 +3507,7 @@ static const struct inode_operations proc_task_inode_operations = {
.lookup = proc_task_lookup,
.getattr = proc_task_getattr,
.setattr = proc_setattr,
+ .permission = proc_pid_permission,
};

static const struct file_operations proc_task_operations = {
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 176ce4c..895e3b1 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -7,6 +7,7 @@
#include <linux/time.h>
#include <linux/proc_fs.h>
#include <linux/kernel.h>
+#include <linux/pid_namespace.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/stat.h>
@@ -17,7 +18,9 @@
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sysctl.h>
+#include <linux/seq_file.h>
#include <linux/slab.h>
+#include <linux/mount.h>

#include <asm/system.h>
#include <asm/uaccess.h>
@@ -93,12 +96,29 @@ void __init proc_init_inodecache(void)
init_once);
}

+static int proc_show_options(struct seq_file *seq, struct vfsmount *vfs)
+{
+ struct super_block *sb = vfs->mnt_sb;
+ struct pid_namespace *pid = sb->s_fs_info;
+
+ if (pid->pid_gid)
+ seq_printf(seq, ",gid=%lu", (unsigned long)pid->pid_gid);
+ if (pid->hide_pid != 0)
+ seq_printf(seq, ",hidepid=%u", pid->hide_pid);
+ if (pid->hide_net)
+ seq_printf(seq, ",hidenet");
+
+ return 0;
+}
+
static const struct super_operations proc_sops = {
.alloc_inode = proc_alloc_inode,
.destroy_inode = proc_destroy_inode,
.drop_inode = generic_delete_inode,
.evict_inode = proc_evict_inode,
.statfs = simple_statfs,
+ .remount_fs = proc_remount,
+ .show_options = proc_show_options,
};

static void __pde_users_dec(struct proc_dir_entry *pde)
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index 9ad561d..1cacb6a 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -110,6 +110,7 @@ void pde_put(struct proc_dir_entry *pde);
extern struct vfsmount *proc_mnt;
int proc_fill_super(struct super_block *);
struct inode *proc_get_inode(struct super_block *, struct proc_dir_entry *);
+int proc_remount(struct super_block *sb, int *flags, char *data);

/*
* These are generic /proc routines that use the internal
diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index 9020ac1..a2a1f08 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -22,10 +22,13 @@
#include <linux/mount.h>
#include <linux/nsproxy.h>
#include <net/net_namespace.h>
+#include <linux/pid_namespace.h>
#include <linux/seq_file.h>

#include "internal.h"

+static struct net *fake_net;
+

static struct net *get_proc_net(const struct inode *inode)
{
@@ -105,6 +108,15 @@ static struct net *get_proc_task_net(struct inode *dir)
struct task_struct *task;
struct nsproxy *ns;
struct net *net = NULL;
+ struct pid_namespace *pid = dir->i_sb->s_fs_info;
+
+ if (pid->hide_net &&
+ !in_group_p(pid->pid_gid) &&
+ !capable(CAP_NET_ADMIN)) {
+ if (fake_net)
+ get_net(fake_net);
+ return fake_net;
+ }

rcu_read_lock();
task = pid_task(proc_pid(dir), PIDTYPE_PID);
@@ -239,3 +251,17 @@ int __init proc_net_init(void)

return register_pernet_subsys(&proc_net_ns_ops);
}
+
+#ifdef CONFIG_NET_NS
+int __init proc_net_initcall(void)
+{
+ fake_net = net_create();
+ if (fake_net == NULL)
+ return -ENOMEM;
+
+ get_net(fake_net);
+ return 0;
+}
+
+late_initcall(proc_net_initcall);
+#endif
diff --git a/fs/proc/root.c b/fs/proc/root.c
index ef9fa8e..10cc071 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -18,6 +18,7 @@
#include <linux/bitops.h>
#include <linux/mount.h>
#include <linux/pid_namespace.h>
+#include <linux/parser.h>

#include "internal.h"

@@ -35,6 +36,76 @@ static int proc_set_super(struct super_block *sb, void *data)
return set_anon_super(sb, NULL);
}

+enum {
+ Opt_gid, Opt_hidepid, Opt_hidenet, Opt_nohidenet, Opt_err,
+};
+
+static const match_table_t tokens = {
+ {Opt_hidepid, "hidepid=%u"},
+ {Opt_gid, "gid=%u"},
+ {Opt_hidenet, "hidenet"},
+ {Opt_nohidenet, "nohidenet"},
+ {Opt_err, NULL},
+};
+
+static int proc_parse_options(char *options, struct pid_namespace *pid)
+{
+ char *p;
+ substring_t args[MAX_OPT_ARGS];
+ int option;
+
+ pr_debug("proc: options = %s\n", options);
+
+ if (!options)
+ return 1;
+
+ while ((p = strsep(&options, ",")) != NULL) {
+ int token;
+ if (!*p)
+ continue;
+
+ args[0].to = args[0].from = 0;
+ token = match_token(p, tokens, args);
+ switch (token) {
+ case Opt_gid:
+ if (match_int(&args[0], &option))
+ return 0;
+ pid->pid_gid = option;
+ break;
+ case Opt_hidepid:
+ if (match_int(&args[0], &option))
+ return 0;
+ if (option < 0 || option > 2) {
+ pr_err("proc: hidepid value must be between 0 and 2.\n");
+ return 0;
+ }
+ pid->hide_pid = option;
+ break;
+ case Opt_hidenet:
+ pid->hide_net = true;
+ break;
+ case Opt_nohidenet:
+ pid->hide_net = false;
+ break;
+ default:
+ pr_err("proc: unrecognized mount option \"%s\" "
+ "or missing value", p);
+ return 0;
+ }
+ }
+
+ pr_debug("proc: gid = %u, hidepid = %o, hidenet = %d\n",
+ pid->pid_gid, pid->hide_pid, (int)pid->hide_net);
+
+ return 1;
+}
+
+int proc_remount(struct super_block *sb, int *flags, char *data)
+{
+ struct pid_namespace *pid = sb->s_fs_info;
+ return !proc_parse_options(data, pid);
+}
+
static struct dentry *proc_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
@@ -42,6 +113,7 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
struct super_block *sb;
struct pid_namespace *ns;
struct proc_inode *ei;
+ char *options;

if (proc_mnt) {
/* Seed the root directory with a pid so it doesn't need
@@ -54,10 +126,13 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
ei->pid = find_get_pid(1);
}

- if (flags & MS_KERNMOUNT)
+ if (flags & MS_KERNMOUNT) {
ns = (struct pid_namespace *)data;
- else
+ options = NULL;
+ } else {
ns = current->nsproxy->pid_ns;
+ options = data;
+ }

sb = sget(fs_type, proc_test_super, proc_set_super, ns);
if (IS_ERR(sb))
@@ -65,6 +140,10 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,

if (!sb->s_root) {
sb->s_flags = flags;
+ if (!proc_parse_options(options, ns)) {
+ deactivate_locked_super(sb);
+ return ERR_PTR(-EINVAL);
+ }
err = proc_fill_super(sb);
if (err) {
deactivate_locked_super(sb);
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 38d1032..1c33094 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -30,6 +30,9 @@ struct pid_namespace {
#ifdef CONFIG_BSD_PROCESS_ACCT
struct bsd_acct_struct *bacct;
#endif
+ gid_t pid_gid;
+ int hide_pid;
+ bool hide_net;
};

extern struct pid_namespace init_pid_ns;
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 1bf812b..d40c61c 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -113,6 +113,8 @@ static inline struct net *copy_net_ns(unsigned long flags, struct net *net_ns)
}
#endif /* CONFIG_NET */

+extern struct net *net_create(void);
+

extern struct list_head net_namespace_list;

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 3f86026..c7c7310 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -216,7 +216,7 @@ static void net_free(struct net *net)
kmem_cache_free(net_cachep, net);
}

-static struct net *net_create(void)
+struct net *net_create(void)
{
struct net *net;
int rv;
--
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