Re: [PATCH] proc: move mount options out of pid_namespace
From: Eric W. Biederman
Date: Wed Jul 10 2013 - 10:59:23 EST
Stephen Mell <sub.atomic.fusion@xxxxxxxxx> writes:
> Currently, the proc mount options hidepid and pidgid are stored on the
> pid_namespace struct that serves as proc's superblock info. As a
> result, mounting proc from the same pid namespace with different mount
> options will change the behaviour of any existing mounts.
>
> This patch creates a new struct, proc_sb_info, which contains the
> mount options and a reference to to the pid namespace. This should
> enable a future patch to make the pid namespace a mount option.
I haven't had much time to think about this but your description leaves
a very important question unanswered. Is it valid/safe to be able to
mount proc with different hidepid and pidgid values for the same pid
namespace.
My concern would be that you would be opening up a security hole for
someone, by allowing those options to change.
At a practical level I wonder in what kind of situation do you want
some mounts of proc to hid proc entries and some mounts of proc not to?
Eric
> Signed-off-by: Stephen Mell <sub.atomic.fusion@xxxxxxxxx>
> ---
> fs/proc/base.c | 41 ++++++++++++++++++------------
> fs/proc/inode.c | 10 ++++----
> fs/proc/internal.h | 8 ++++++
> fs/proc/root.c | 58 +++++++++++++++++++++++++------------------
> fs/proc/self.c | 10 +++++---
> include/linux/pid_namespace.h | 3 ---
> 6 files changed, 78 insertions(+), 52 deletions(-)
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 1485e38..db119ef 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -584,13 +584,13 @@ int proc_setattr(struct dentry *dentry, struct iattr *attr)
> * 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,
> +static bool has_pid_permissions(struct proc_sb_info *fsi,
> struct task_struct *task,
> int hide_pid_min)
> {
> - if (pid->hide_pid < hide_pid_min)
> + if (fsi->hide_pid < hide_pid_min)
> return true;
> - if (in_group_p(pid->pid_gid))
> + if (in_group_p(fsi->pid_gid))
> return true;
> return ptrace_may_access(task, PTRACE_MODE_READ);
> }
> @@ -598,18 +598,18 @@ static bool has_pid_permissions(struct pid_namespace *pid,
>
> static int proc_pid_permission(struct inode *inode, int mask)
> {
> - struct pid_namespace *pid = inode->i_sb->s_fs_info;
> + struct proc_sb_info *fsi = inode->i_sb->s_fs_info;
> struct task_struct *task;
> bool has_perms;
>
> task = get_proc_task(inode);
> if (!task)
> return -ESRCH;
> - has_perms = has_pid_permissions(pid, task, 1);
> + has_perms = has_pid_permissions(fsi, task, 1);
> put_task_struct(task);
>
> if (!has_perms) {
> - if (pid->hide_pid == 2) {
> + if (fsi->hide_pid == 2) {
> /*
> * Let's make getdents(), stat(), and open()
> * consistent with each other. If a process
> @@ -670,12 +670,14 @@ static const struct file_operations proc_info_file_operations = {
> static int proc_single_show(struct seq_file *m, void *v)
> {
> struct inode *inode = m->private;
> + struct proc_sb_info *fsi;
> struct pid_namespace *ns;
> struct pid *pid;
> struct task_struct *task;
> int ret;
>
> - ns = inode->i_sb->s_fs_info;
> + fsi = inode->i_sb->s_fs_info;
> + ns = fsi->ns;
> pid = proc_pid(inode);
> task = get_pid_task(pid, PIDTYPE_PID);
> if (!task)
> @@ -1574,7 +1576,7 @@ 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;
> + struct proc_sb_info *fsi = dentry->d_sb->s_fs_info;
>
> generic_fillattr(inode, stat);
>
> @@ -1583,7 +1585,7 @@ int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
> stat->gid = GLOBAL_ROOT_GID;
> task = pid_task(proc_pid(inode), PIDTYPE_PID);
> if (task) {
> - if (!has_pid_permissions(pid, task, 2)) {
> + if (!has_pid_permissions(fsi, task, 2)) {
> rcu_read_unlock();
> /*
> * This doesn't prevent learning whether PID exists,
> @@ -2111,7 +2113,7 @@ static int proc_timers_open(struct inode *inode, struct file *file)
> return -ENOMEM;
>
> tp->pid = proc_pid(inode);
> - tp->ns = inode->i_sb->s_fs_info;
> + tp->ns = inode->i_sb->s_fs_info->ns;
> return 0;
> }
>
> @@ -2800,13 +2802,15 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, unsign
> int result = 0;
> struct task_struct *task;
> unsigned tgid;
> + struct proc_sb_info *fsi;
> struct pid_namespace *ns;
>
> tgid = name_to_int(dentry);
> if (tgid == ~0U)
> goto out;
>
> - ns = dentry->d_sb->s_fs_info;
> + fsi = dentry->d_sb->s_fs_info;
> + ns = fsi->ns;
> rcu_read_lock();
> task = find_task_by_pid_ns(tgid, ns);
> if (task)
> @@ -2870,14 +2874,15 @@ retry:
> int proc_pid_readdir(struct file *file, struct dir_context *ctx)
> {
> struct tgid_iter iter;
> - struct pid_namespace *ns = file->f_dentry->d_sb->s_fs_info;
> + struct proc_sb_info *fsi = file->f_dentry->d_sb->s_fs_info;
> + struct pid_namespace *ns = fsi->ns;
> loff_t pos = ctx->pos;
>
> if (pos >= PID_MAX_LIMIT + TGID_OFFSET)
> return 0;
>
> if (pos == TGID_OFFSET - 1) {
> - struct inode *inode = ns->proc_self->d_inode;
> + struct inode *inode = fsi->proc_self->d_inode;
> if (!dir_emit(ctx, "self", 4, inode->i_ino, DT_LNK))
> return 0;
> iter.tgid = 0;
> @@ -2890,7 +2895,7 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
> iter.tgid += 1, iter = next_tgid(ns, iter)) {
> char name[PROC_NUMBUF];
> int len;
> - if (!has_pid_permissions(ns, iter.task, 2))
> + if (!has_pid_permissions(fsi, iter.task, 2))
> continue;
>
> len = snprintf(name, sizeof(name), "%d", iter.tgid);
> @@ -3045,6 +3050,7 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
> struct task_struct *task;
> struct task_struct *leader = get_proc_task(dir);
> unsigned tid;
> + struct proc_sb_info *fsi;
> struct pid_namespace *ns;
>
> if (!leader)
> @@ -3054,7 +3060,8 @@ static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry
> if (tid == ~0U)
> goto out;
>
> - ns = dentry->d_sb->s_fs_info;
> + fsi = dentry->d_sb->s_fs_info;
> + ns = fsi->ns;
> rcu_read_lock();
> task = find_task_by_pid_ns(tid, ns);
> if (task)
> @@ -3148,6 +3155,7 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx)
> {
> struct task_struct *leader = NULL;
> struct task_struct *task = get_proc_task(file_inode(file));
> + struct proc_sb_info *fsi;
> struct pid_namespace *ns;
> int tid;
>
> @@ -3169,7 +3177,8 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx)
> /* f_version caches the tgid value that the last readdir call couldn't
> * return. lseek aka telldir automagically resets f_version to 0.
> */
> - ns = file->f_dentry->d_sb->s_fs_info;
> + fsi = file->f_dentry->d_sb->s_fs_info;
> + ns = fsi->ns;
> tid = (int)file->f_version;
> file->f_version = 0;
> for (task = first_tid(leader, tid, ctx->pos - 2, ns);
> diff --git a/fs/proc/inode.c b/fs/proc/inode.c
> index 073aea6..148737d 100644
> --- a/fs/proc/inode.c
> +++ b/fs/proc/inode.c
> @@ -110,12 +110,12 @@ 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;
> + struct proc_sb_info *fsi = sb->s_fs_info;
>
> - if (!gid_eq(pid->pid_gid, GLOBAL_ROOT_GID))
> - seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, pid->pid_gid));
> - if (pid->hide_pid != 0)
> - seq_printf(seq, ",hidepid=%u", pid->hide_pid);
> + if (!gid_eq(fsi->pid_gid, GLOBAL_ROOT_GID))
> + seq_printf(seq, ",gid=%u", from_kgid_munged(&init_user_ns, fsi->pid_gid));
> + if (fsi->hide_pid != 0)
> + seq_printf(seq, ",hidepid=%u", fsi->hide_pid);
>
> return 0;
> }
> diff --git a/fs/proc/internal.h b/fs/proc/internal.h
> index 651d09a..885f542 100644
> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -29,6 +29,14 @@ struct mempolicy;
> * /proc file has a parent, but "subdir" is NULL for all
> * non-directory entries).
> */
> +
> +struct proc_sb_info {
> + struct pid_namespace *ns;
> + struct dentry *proc_self;
> + kgid_t pid_gid;
> + int hide_pid;
> +};
> +
> struct proc_dir_entry {
> unsigned int low_ino;
> umode_t mode;
> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index 229e366..f8e97d6 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -20,6 +20,7 @@
> #include <linux/mount.h>
> #include <linux/pid_namespace.h>
> #include <linux/parser.h>
> +#include <linux/slab.h>
>
> #include "internal.h"
>
> @@ -31,10 +32,9 @@ static int proc_test_super(struct super_block *sb, void *data)
> static int proc_set_super(struct super_block *sb, void *data)
> {
> int err = set_anon_super(sb, NULL);
> - if (!err) {
> - struct pid_namespace *ns = (struct pid_namespace *)data;
> - sb->s_fs_info = get_pid_ns(ns);
> - }
> + if (!err)
> + sb->s_fs_info = (struct proc_sb_info *)data;
> +
> return err;
> }
>
> @@ -48,7 +48,7 @@ static const match_table_t tokens = {
> {Opt_err, NULL},
> };
>
> -static int proc_parse_options(char *options, struct pid_namespace *pid)
> +static int proc_parse_options(char *options, struct proc_sb_info *fsi)
> {
> char *p;
> substring_t args[MAX_OPT_ARGS];
> @@ -68,7 +68,7 @@ static int proc_parse_options(char *options, struct pid_namespace *pid)
> case Opt_gid:
> if (match_int(&args[0], &option))
> return 0;
> - pid->pid_gid = make_kgid(current_user_ns(), option);
> + fsi->pid_gid = make_kgid(current_user_ns(), option);
> break;
> case Opt_hidepid:
> if (match_int(&args[0], &option))
> @@ -77,7 +77,7 @@ static int proc_parse_options(char *options, struct pid_namespace *pid)
> pr_err("proc: hidepid value must be between 0 and 2.\n");
> return 0;
> }
> - pid->hide_pid = option;
> + fsi->hide_pid = option;
> break;
> default:
> pr_err("proc: unrecognized mount option \"%s\" "
> @@ -91,36 +91,44 @@ static int proc_parse_options(char *options, struct pid_namespace *pid)
>
> 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);
> + struct proc_sb_info *fsi = sb->s_fs_info;
> + return !proc_parse_options(data, fsi);
> }
>
> static struct dentry *proc_mount(struct file_system_type *fs_type,
> int flags, const char *dev_name, void *data)
> {
> int err;
> + struct proc_sb_info *fsi;
> struct super_block *sb;
> - struct pid_namespace *ns;
> char *options;
>
> + fsi = kzalloc(sizeof(struct proc_sb_info), GFP_KERNEL);
> + if (!fsi)
> + return ERR_PTR(-ENOMEM);
> +
> + sb = sget(fs_type, proc_test_super, proc_set_super, flags, fsi);
> + if (IS_ERR(sb))
> + return ERR_CAST(sb);
> +
> if (flags & MS_KERNMOUNT) {
> - ns = (struct pid_namespace *)data;
> + fsi->ns = (struct pid_namespace *)data;
> + get_pid_ns(fsi->ns);
> options = NULL;
> } else {
> - ns = task_active_pid_ns(current);
> - options = data;
> -
> if (!current_user_ns()->may_mount_proc)
> return ERR_PTR(-EPERM);
> - }
>
> - sb = sget(fs_type, proc_test_super, proc_set_super, flags, ns);
> - if (IS_ERR(sb))
> - return ERR_CAST(sb);
> + options = data;
> + if (!proc_parse_options(options, fsi)) {
> + deactivate_locked_super(sb);
> + return ERR_PTR(-EINVAL);
> + }
>
> - if (!proc_parse_options(options, ns)) {
> - deactivate_locked_super(sb);
> - return ERR_PTR(-EINVAL);
> + if (!fsi->ns) {
> + fsi->ns = task_active_pid_ns(current);
> + get_pid_ns(fsi->ns);
> + }
> }
>
> if (!sb->s_root) {
> @@ -138,13 +146,15 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
>
> static void proc_kill_sb(struct super_block *sb)
> {
> + struct proc_sb_info *fsi;
> struct pid_namespace *ns;
>
> - ns = (struct pid_namespace *)sb->s_fs_info;
> - if (ns->proc_self)
> - dput(ns->proc_self);
> + fsi = (struct proc_sb_info *)sb->s_fs_info;
> + ns = (struct pid_namespace *)fsi->ns;
> + dput(fsi->proc_self);
> kill_anon_super(sb);
> put_pid_ns(ns);
> + kfree(fsi);
> }
>
> static struct file_system_type proc_fs_type = {
> diff --git a/fs/proc/self.c b/fs/proc/self.c
> index 6b6a993..ff4a2e2 100644
> --- a/fs/proc/self.c
> +++ b/fs/proc/self.c
> @@ -10,7 +10,8 @@
> static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
> int buflen)
> {
> - struct pid_namespace *ns = dentry->d_sb->s_fs_info;
> + struct proc_sb_info *fsi = dentry->d_sb->s_fs_info;
> + struct pid_namespace *ns = fsi->ns;
> pid_t tgid = task_tgid_nr_ns(current, ns);
> char tmp[PROC_NUMBUF];
> if (!tgid)
> @@ -21,7 +22,8 @@ static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
>
> static void *proc_self_follow_link(struct dentry *dentry, struct nameidata *nd)
> {
> - struct pid_namespace *ns = dentry->d_sb->s_fs_info;
> + struct proc_sb_info *fsi = dentry->d_sb->s_fs_info;
> + struct pid_namespace *ns = fsi->ns;
> pid_t tgid = task_tgid_nr_ns(current, ns);
> char *name = ERR_PTR(-ENOENT);
> if (tgid) {
> @@ -55,7 +57,7 @@ static unsigned self_inum;
> int proc_setup_self(struct super_block *s)
> {
> struct inode *root_inode = s->s_root->d_inode;
> - struct pid_namespace *ns = s->s_fs_info;
> + struct proc_sb_info *fsi = s->s_fs_info;
> struct dentry *self;
>
> mutex_lock(&root_inode->i_mutex);
> @@ -82,7 +84,7 @@ int proc_setup_self(struct super_block *s)
> pr_err("proc_fill_super: can't allocate /proc/self\n");
> return PTR_ERR(self);
> }
> - ns->proc_self = self;
> + fsi->proc_self = self;
> return 0;
> }
>
> diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> index e277266..6185386 100644
> --- a/include/linux/pid_namespace.h
> +++ b/include/linux/pid_namespace.h
> @@ -31,15 +31,12 @@ struct pid_namespace {
> struct pid_namespace *parent;
> #ifdef CONFIG_PROC_FS
> struct vfsmount *proc_mnt;
> - struct dentry *proc_self;
> #endif
> #ifdef CONFIG_BSD_PROCESS_ACCT
> struct bsd_acct_struct *bacct;
> #endif
> struct user_namespace *user_ns;
> struct work_struct proc_work;
> - kgid_t pid_gid;
> - int hide_pid;
> int reboot; /* group exit code if this pidns was rebooted */
> unsigned int proc_inum;
> };
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/