From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.kundenserver.de ([212.227.126.135]:45233 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725799AbeJDFla (ORCPT ); Thu, 4 Oct 2018 01:41:30 -0400 From: Laurent Vivier To: linux-kernel@vger.kernel.org Cc: Dmitry Safonov , Alexander Viro , Jann Horn , linux-fsdevel@vger.kernel.org, James Bottomley , Andrei Vagin , containers@lists.linux-foundation.org, Eric Biederman , linux-api@vger.kernel.org, Laurent Vivier Subject: [RFC v3 1/1] ns: add binfmt_misc to the user namespace Date: Thu, 4 Oct 2018 00:50:22 +0200 Message-Id: <20181003225022.32033-2-laurent@vivier.eu> In-Reply-To: <20181003225022.32033-1-laurent@vivier.eu> References: <20181003225022.32033-1-laurent@vivier.eu> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: This patch allows to have a different binfmt_misc configuration for each new user namespace. By default, the binfmt_misc configuration is the one of the host, but if the binfmt_misc filesystem is mounted in the new namespace a new empty binfmt instance is created and used in this namespace. For instance, using "unshare" we can start a chroot of an another architecture and configure the binfmt_misc interpreter without being root to run the binaries in this chroot. Signed-off-by: Laurent Vivier --- fs/binfmt_misc.c | 85 +++++++++++++++++++++++----------- include/linux/user_namespace.h | 15 ++++++ kernel/user.c | 14 ++++++ kernel/user_namespace.c | 9 ++++ 4 files changed, 95 insertions(+), 28 deletions(-) diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c index aa4a7a23ff99..78780bc87506 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -38,9 +38,6 @@ enum { VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */ }; -static LIST_HEAD(entries); -static int enabled = 1; - enum {Enabled, Magic}; #define MISC_FMT_PRESERVE_ARGV0 (1 << 31) #define MISC_FMT_OPEN_BINARY (1 << 30) @@ -60,10 +57,7 @@ typedef struct { struct file *interp_file; } Node; -static DEFINE_RWLOCK(entries_lock); static struct file_system_type bm_fs_type; -static struct vfsmount *bm_mnt; -static int entry_count; /* * Max length of the register string. Determined by: @@ -85,13 +79,13 @@ static int entry_count; * if we do, return the node, else NULL * locking is done in load_misc_binary */ -static Node *check_file(struct linux_binprm *bprm) +static Node *check_file(struct user_namespace *ns, struct linux_binprm *bprm) { char *p = strrchr(bprm->interp, '.'); struct list_head *l; /* Walk all the registered handlers. */ - list_for_each(l, &entries) { + list_for_each(l, &ns->binfmt_ns->entries) { Node *e = list_entry(l, Node, list); char *s; int j; @@ -133,17 +127,18 @@ static int load_misc_binary(struct linux_binprm *bprm) struct file *interp_file = NULL; int retval; int fd_binary = -1; + struct user_namespace *ns = current_user_ns(); retval = -ENOEXEC; - if (!enabled) + if (!ns->binfmt_ns->enabled) return retval; /* to keep locking time low, we copy the interpreter string */ - read_lock(&entries_lock); - fmt = check_file(bprm); + read_lock(&ns->binfmt_ns->entries_lock); + fmt = check_file(ns ,bprm); if (fmt) dget(fmt->dentry); - read_unlock(&entries_lock); + read_unlock(&ns->binfmt_ns->entries_lock); if (!fmt) return retval; @@ -609,19 +604,19 @@ static void bm_evict_inode(struct inode *inode) kfree(e); } -static void kill_node(Node *e) +static void kill_node(struct user_namespace *ns, Node *e) { struct dentry *dentry; - write_lock(&entries_lock); + write_lock(&ns->binfmt_ns->entries_lock); list_del_init(&e->list); - write_unlock(&entries_lock); + write_unlock(&ns->binfmt_ns->entries_lock); dentry = e->dentry; drop_nlink(d_inode(dentry)); d_drop(dentry); dput(dentry); - simple_release_fs(&bm_mnt, &entry_count); + simple_release_fs(&ns->binfmt_ns->bm_mnt, &ns->binfmt_ns->entry_count); } /* / */ @@ -651,6 +646,7 @@ static ssize_t bm_entry_write(struct file *file, const char __user *buffer, struct dentry *root; Node *e = file_inode(file)->i_private; int res = parse_command(buffer, count); + struct user_namespace *ns = file->f_path.dentry->d_sb->s_user_ns; switch (res) { case 1: @@ -667,7 +663,7 @@ static ssize_t bm_entry_write(struct file *file, const char __user *buffer, inode_lock(d_inode(root)); if (!list_empty(&e->list)) - kill_node(e); + kill_node(ns, e); inode_unlock(d_inode(root)); break; @@ -693,6 +689,7 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, struct inode *inode; struct super_block *sb = file_inode(file)->i_sb; struct dentry *root = sb->s_root, *dentry; + struct user_namespace *ns = file->f_path.dentry->d_sb->s_user_ns; int err = 0; e = create_entry(buffer, count); @@ -716,7 +713,8 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, if (!inode) goto out2; - err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count); + err = simple_pin_fs(&bm_fs_type, &ns->binfmt_ns->bm_mnt, + &ns->binfmt_ns->entry_count); if (err) { iput(inode); inode = NULL; @@ -725,12 +723,16 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, if (e->flags & MISC_FMT_OPEN_FILE) { struct file *f; + const struct cred *old_cred; + old_cred = override_creds(file->f_cred); f = open_exec(e->interpreter); + revert_creds(old_cred); if (IS_ERR(f)) { err = PTR_ERR(f); pr_notice("register: failed to install interpreter file %s\n", e->interpreter); - simple_release_fs(&bm_mnt, &entry_count); + simple_release_fs(&ns->binfmt_ns->bm_mnt, + &ns->binfmt_ns->entry_count); iput(inode); inode = NULL; goto out2; @@ -743,9 +745,9 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, inode->i_fop = &bm_entry_operations; d_instantiate(dentry, inode); - write_lock(&entries_lock); - list_add(&e->list, &entries); - write_unlock(&entries_lock); + write_lock(&ns->binfmt_ns->entries_lock); + list_add(&e->list, &ns->binfmt_ns->entries); + write_unlock(&ns->binfmt_ns->entries_lock); err = 0; out2: @@ -770,7 +772,8 @@ static const struct file_operations bm_register_operations = { static ssize_t bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { - char *s = enabled ? "enabled\n" : "disabled\n"; + struct user_namespace *ns = file->f_path.dentry->d_sb->s_user_ns; + char *s = ns->binfmt_ns->enabled ? "enabled\n" : "disabled\n"; return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s)); } @@ -778,25 +781,27 @@ bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) static ssize_t bm_status_write(struct file *file, const char __user *buffer, size_t count, loff_t *ppos) { + struct user_namespace *ns = file->f_path.dentry->d_sb->s_user_ns; int res = parse_command(buffer, count); struct dentry *root; switch (res) { case 1: /* Disable all handlers. */ - enabled = 0; + ns->binfmt_ns->enabled = 0; break; case 2: /* Enable all handlers. */ - enabled = 1; + ns->binfmt_ns->enabled = 1; break; case 3: /* Delete all handlers. */ root = file_inode(file)->i_sb->s_root; inode_lock(d_inode(root)); - while (!list_empty(&entries)) - kill_node(list_first_entry(&entries, Node, list)); + while (!list_empty(&ns->binfmt_ns->entries)) + kill_node(ns, list_first_entry(&ns->binfmt_ns->entries, + Node, list)); inode_unlock(d_inode(root)); break; @@ -838,7 +843,30 @@ static int bm_fill_super(struct super_block *sb, void *data, int silent) static struct dentry *bm_mount(struct file_system_type *fs_type, int flags, const char *dev_name, void *data) { - return mount_single(fs_type, flags, data, bm_fill_super); + struct user_namespace *ns = current_user_ns(); + + /* create a new binfmt namespace + * if we are not in the first user namespace + * but the binfmt namespace is the first one + */ + if (ns != &init_user_ns && ns->binfmt_ns == &init_binfmt_ns) { + struct binfmt_namespace *binfmt_ns; + + binfmt_ns = kmalloc(sizeof(struct binfmt_namespace), + GFP_KERNEL); + if (binfmt_ns == NULL) { + return ERR_PTR(-ENOMEM); + } + INIT_LIST_HEAD(&binfmt_ns->entries); + binfmt_ns->enabled = 1; + rwlock_init(&binfmt_ns->entries_lock); + binfmt_ns->bm_mnt = NULL; + binfmt_ns->entry_count = 0; + ns->binfmt_ns = binfmt_ns; + } + + return mount_ns(fs_type, flags, data, ns, ns, + bm_fill_super); } static struct linux_binfmt misc_format = { @@ -849,6 +877,7 @@ static struct linux_binfmt misc_format = { static struct file_system_type bm_fs_type = { .owner = THIS_MODULE, .name = "binfmt_misc", + .fs_flags = FS_USERNS_MOUNT, .mount = bm_mount, .kill_sb = kill_litter_super, }; diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index d6b74b91096b..319141da5315 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -52,6 +52,18 @@ enum ucount_type { UCOUNT_COUNTS, }; +#if IS_ENABLED(CONFIG_BINFMT_MISC) +struct binfmt_namespace { + struct list_head entries; + rwlock_t entries_lock; + int enabled; + struct vfsmount *bm_mnt; + int entry_count; +} __randomize_layout; + +extern struct binfmt_namespace init_binfmt_ns; +#endif + struct user_namespace { struct uid_gid_map uid_map; struct uid_gid_map gid_map; @@ -76,6 +88,9 @@ struct user_namespace { #endif struct ucounts *ucounts; int ucount_max[UCOUNT_COUNTS]; +#if IS_ENABLED(CONFIG_BINFMT_MISC) + struct binfmt_namespace *binfmt_ns; +#endif } __randomize_layout; struct ucounts { diff --git a/kernel/user.c b/kernel/user.c index 0df9b1640b2a..220ab2053d44 100644 --- a/kernel/user.c +++ b/kernel/user.c @@ -19,6 +19,17 @@ #include #include +#if IS_ENABLED(CONFIG_BINFMT_MISC) +struct binfmt_namespace init_binfmt_ns = { + .entries = LIST_HEAD_INIT(init_binfmt_ns.entries), + .enabled = 1, + .entries_lock = __RW_LOCK_UNLOCKED(init_binfmt_ns.entries_lock), + .bm_mnt = NULL, + .entry_count = 0, +}; +EXPORT_SYMBOL_GPL(init_binfmt_ns); +#endif + /* * userns count is 1 for root user, 1 for init_uts_ns, * and 1 for... ? @@ -66,6 +77,9 @@ struct user_namespace init_user_ns = { .persistent_keyring_register_sem = __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem), #endif +#if IS_ENABLED(CONFIG_BINFMT_MISC) + .binfmt_ns = &init_binfmt_ns, +#endif }; EXPORT_SYMBOL_GPL(init_user_ns); diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index e5222b5fb4fe..dec0ab4a729a 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -140,6 +140,10 @@ int create_user_ns(struct cred *new) if (!setup_userns_sysctls(ns)) goto fail_keyring; +#if IS_ENABLED(CONFIG_BINFMT_MISC) + ns->binfmt_ns = &init_binfmt_ns; +#endif + set_cred_user_ns(new, ns); return 0; fail_keyring: @@ -195,6 +199,11 @@ static void free_user_ns(struct work_struct *work) kfree(ns->projid_map.forward); kfree(ns->projid_map.reverse); } +#if IS_ENABLED(CONFIG_BINFMT_MISC) + if (ns->binfmt_ns != &init_binfmt_ns) { + kfree(ns->binfmt_ns); + } +#endif retire_userns_sysctls(ns); #ifdef CONFIG_PERSISTENT_KEYRINGS key_put(ns->persistent_keyring_register); -- 2.17.1