5 files changed, 135 insertions, 4 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 0ec91f03422e..12fee132fbe2 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
@@ -1542,3 +1544,40 @@ 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.
+        gid=            Set the group authorized to learn processes 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, sched*, status are now protected against
+other users.  This makes it 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 "kill -0 $PID"),
+but it hides process' uid and gid, which may be learned by stat()'ing
+/proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
+information 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.
+
+gid= defines a group authorized to learn processes information otherwise
+prohibited by hidepid=.  If you use some daemon like identd which needs to learn
+information about processes information, just add identd to this group.
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 4d755fed3ecb..8173dfd89cb2 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -631,6 +631,50 @@ int proc_setattr(struct dentry *dentry, struct iattr *attr)
         return 0;
 }
 
+/*
+ * May current process learn task's sched/cmdline info (for hide_pid_min=1)
+ * or euid/egid (for hide_pid_min=2)?
+ */
+static bool has_pid_permissions(struct pid_namespace *pid,
+                                 struct task_struct *task,
+                                 int hide_pid_min)
+{
+        if (pid->hide_pid < hide_pid_min)
+                return true;
+        if (in_group_p(pid->pid_gid))
+                return true;
+        return ptrace_may_access(task, PTRACE_MODE_READ);
+}
+
+
+static int proc_pid_permission(struct inode *inode, int mask)
+{
+        struct pid_namespace *pid = inode->i_sb->s_fs_info;
+        struct task_struct *task;
+        bool has_perms;
+
+        task = get_proc_task(inode);
+        has_perms = has_pid_permissions(pid, task, 1);
+        put_task_struct(task);
+
+        if (!has_perms) {
+                if (pid->hide_pid == 2) {
+                        /*
+                         * Let's make getdents(), stat(), and open()
+                         * consistent with each other.  If a process
+                         * may not stat() a file, it shouldn't be seen
+                         * in procfs at all.
+                         */
+                        return -ENOENT;
+                }
+
+                return -EPERM;
+        }
+        return generic_permission(inode, mask);
+}
+
+
+
 static const struct inode_operations proc_def_inode_operations = {
         .setattr        = proc_setattr,
 };
@@ -1615,6 +1659,7 @@ int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
         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);
 
@@ -1623,6 +1668,14 @@ int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
         stat->gid = 0;
         task = pid_task(proc_pid(inode), PIDTYPE_PID);
         if (task) {
+                if (!has_pid_permissions(pid, task, 2)) {
+                        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);
@@ -3119,6 +3172,7 @@ 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)
@@ -3322,6 +3376,12 @@ 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)
 {
@@ -3329,6 +3389,7 @@ int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
         struct task_struct *reaper;
         struct tgid_iter iter;
         struct pid_namespace *ns;
+        filldir_t __filldir;
 
         if (filp->f_pos >= PID_MAX_LIMIT + TGID_OFFSET)
                 goto out_no_task;
@@ -3350,8 +3411,13 @@ 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 (has_pid_permissions(ns, iter.task, 2))
+                        __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;
                 }
@@ -3686,6 +3752,7 @@ 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 27c762f34870..84fd3235a590 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -106,6 +106,14 @@ void __init proc_init_inodecache(void)
 
 static int proc_show_options(struct seq_file *seq, struct dentry *root)
 {
+        struct super_block *sb = root->d_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);
+
         return 0;
 }
 
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 6a8ac1d361a9..46a15d8a29ca 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -38,10 +38,12 @@ static int proc_set_super(struct super_block *sb, void *data)
 }
 
 enum {
-        Opt_err,
+        Opt_gid, Opt_hidepid, Opt_err,
 };
 
 static const match_table_t tokens = {
+        {Opt_hidepid, "hidepid=%u"},
+        {Opt_gid, "gid=%u"},
         {Opt_err, NULL},
 };
 
@@ -49,8 +51,7 @@ static int proc_parse_options(char *options, struct pid_namespace *pid)
 {
         char *p;
         substring_t args[MAX_OPT_ARGS];
-
-        pr_debug("proc: options = %s\n", options);
+        int option;
 
         if (!options)
                 return 1;
@@ -63,6 +64,20 @@ static int proc_parse_options(char *options, struct pid_namespace *pid)
                 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;
                 default:
                         pr_err("proc: unrecognized mount option \"%s\" "
                                "or missing value\n", p);
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 38d10326246a..e7cf6669ac34 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -30,6 +30,8 @@ struct pid_namespace {
 #ifdef CONFIG_BSD_PROCESS_ACCT
         struct bsd_acct_struct *bacct;
 #endif
+        gid_t pid_gid;
+        int hide_pid;
 };
 
 extern struct pid_namespace init_pid_ns;