From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DE834C433E9 for ; Mon, 18 Jan 2021 20:01:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B670922C9D for ; Mon, 18 Jan 2021 20:01:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437381AbhART7b (ORCPT ); Mon, 18 Jan 2021 14:59:31 -0500 Received: from mout.kundenserver.de ([217.72.192.75]:46803 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2437697AbhARTyh (ORCPT ); Mon, 18 Jan 2021 14:54:37 -0500 Received: from [192.168.100.1] ([82.252.149.54]) by mrelayeu.kundenserver.de (mreue109 [213.165.67.119]) with ESMTPSA (Nemesis) id 1M4bA0-1l123l1oso-001fdq; Mon, 18 Jan 2021 20:51:27 +0100 Subject: Re: [PATCH v8 1/1] ns: add binfmt_misc to the user namespace To: Jan Kiszka , linux-kernel@vger.kernel.org Cc: Greg Kurz , Jann Horn , Andrei Vagin , linux-api@vger.kernel.org, Dmitry Safonov , James Bottomley , Christian Brauner , linux-fsdevel@vger.kernel.org, containers@lists.linux-foundation.org, Alexander Viro , Eric Biederman , Henning Schild , =?UTF-8?Q?C=c3=a9dric_Le_Goate?= =?UTF-8?Q?r?= References: <20191216091220.465626-1-laurent@vivier.eu> <20191216091220.465626-2-laurent@vivier.eu> <4fabc6a4-0e8d-11ad-5757-467f15dc96ee@siemens.com> From: Laurent Vivier Message-ID: <8eb5498d-89f6-e39e-d757-404cc3cfaa5c@vivier.eu> Date: Mon, 18 Jan 2021 20:51:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <4fabc6a4-0e8d-11ad-5757-467f15dc96ee@siemens.com> Content-Type: text/plain; charset=utf-8 Content-Language: fr Content-Transfer-Encoding: 8bit X-Provags-ID: V03:K1:vGCdNoXg98BTa/6NlWBXiaJ+fVxZTS3UKDE8Bmz2DJ8pM7h44Sl +6vd7L7qqmQMSf0I45qdd+W9mKe8Y/GO1FiRI7l5w3G68E2b/8r+PlXBMmgrEvIoo75E2YT bgqZg2S/FIbFJFyvoZVtpSd7txnbC7OCe3thH0PnB0Wi/XjsVq1T3rZLqk0LolZlNC7Tb5i iBXhBhoYnL6ktYNyDOVxA== X-UI-Out-Filterresults: notjunk:1;V03:K0:mJgANQA/Y/8=:X9nYmDUIXu5kS+4eQ8QozS +TZ+9M2Nc7HwsfV9d7UONJGZVnsuOUh06xoYgqYHCHKHRYHhSoLjfwKZqmePemJqUYjAn9LeZ tv/xKQcnu6eJSIy1pxOv1xaDmZM9UpM1S1zmM7IJCrNfx+GNebm33rzgUoQGbdsaRGycsI5ep K8J5siwhSPQh4H+9VOWCP/CCROXvzMbYCfQtUTlP0l408o1v3pbs7c/6Lr6JRkG5LfRbs5ksL 99zHs8jJsEgjtdQ0tZvHn62AinApMNgOHedtnHr8y/vy2BJpTf4DKKLO4TGGzSZLaeqWEoCE/ Cwz3wIbfU8zYJXnGfQGh7Xt7maKX8jTcv0wkqfS+27Qphl9D3RjGbWMVKJiZUdFebIVW+a5ip BfvgUn1681ACRmK5vavYsJLivTwVGinB641jYRg40UoF9ZvE4fceushgo1Y3svLMT4AvJrMdq wMv3Ox/UmA== Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 08/01/2021 à 09:22, Jan Kiszka a écrit : > On 16.12.19 10:12, Laurent Vivier wrote: >> 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 previous level, 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 another >> architecture and configure the binfmt_misc interpreter without being root >> to run the binaries in this chroot. >> >> Signed-off-by: Laurent Vivier >> Acked-by: Andrei Vagin >> Tested-by: Henning Schild >> --- >> fs/binfmt_misc.c | 115 +++++++++++++++++++++++++-------- >> include/linux/user_namespace.h | 15 +++++ >> kernel/user.c | 14 ++++ >> kernel/user_namespace.c | 3 + >> 4 files changed, 119 insertions(+), 28 deletions(-) >> >> diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c >> index cdb45829354d..17fa1f56ca2e 100644 >> --- a/fs/binfmt_misc.c >> +++ b/fs/binfmt_misc.c >> @@ -40,9 +40,6 @@ 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) >> @@ -62,10 +59,7 @@ 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: >> @@ -82,18 +76,37 @@ static int entry_count; >> */ >> #define MAX_REGISTER_LENGTH 1920 >> >> +static struct binfmt_namespace *binfmt_ns(struct user_namespace *ns) >> +{ >> + struct binfmt_namespace *b_ns; >> + >> + while (ns) { >> + b_ns = READ_ONCE(ns->binfmt_ns); >> + if (b_ns) >> + return b_ns; >> + ns = ns->parent; >> + } >> + /* as the first user namespace is initialized with >> + * &init_binfmt_ns we should never come here >> + * but we try to stay safe by logging a warning >> + * and returning a sane value >> + */ >> + WARN_ON_ONCE(1); >> + return &init_binfmt_ns; >> +} >> + >> /* >> * Check if we support the binfmt >> * 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 binfmt_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->entries) { >> Node *e = list_entry(l, Node, list); >> char *s; >> int j; >> @@ -135,17 +148,18 @@ static int load_misc_binary(struct linux_binprm *bprm) >> struct file *interp_file = NULL; >> int retval; >> int fd_binary = -1; >> + struct binfmt_namespace *ns = binfmt_ns(current_user_ns()); >> >> retval = -ENOEXEC; >> - if (!enabled) >> + if (!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->entries_lock); >> + fmt = check_file(ns, bprm); >> if (fmt) >> dget(fmt->dentry); >> - read_unlock(&entries_lock); >> + read_unlock(&ns->entries_lock); >> if (!fmt) >> return retval; >> >> @@ -611,19 +625,19 @@ static void bm_evict_inode(struct inode *inode) >> kfree(e); >> } >> >> -static void kill_node(Node *e) >> +static void kill_node(struct binfmt_namespace *ns, Node *e) >> { >> struct dentry *dentry; >> >> - write_lock(&entries_lock); >> + write_lock(&ns->entries_lock); >> list_del_init(&e->list); >> - write_unlock(&entries_lock); >> + write_unlock(&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->bm_mnt, &ns->entry_count); >> } >> >> /* / */ >> @@ -653,6 +667,9 @@ 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 binfmt_namespace *ns; >> + >> + ns = binfmt_ns(file_dentry(file)->d_sb->s_user_ns); >> >> switch (res) { >> case 1: >> @@ -669,7 +686,7 @@ 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; >> @@ -695,6 +712,7 @@ 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 binfmt_namespace *ns; >> int err = 0; >> >> e = create_entry(buffer, count); >> @@ -718,7 +736,9 @@ 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); >> + ns = binfmt_ns(file_dentry(file)->d_sb->s_user_ns); >> + err = simple_pin_fs(&bm_fs_type, &ns->bm_mnt, >> + &ns->entry_count); >> if (err) { >> iput(inode); >> inode = NULL; >> @@ -727,12 +747,16 @@ 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->bm_mnt, >> + &ns->entry_count); >> iput(inode); >> inode = NULL; >> goto out2; >> @@ -745,9 +769,9 @@ 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->entries_lock); >> + list_add(&e->list, &ns->entries); >> + write_unlock(&ns->entries_lock); >> >> err = 0; >> out2: >> @@ -772,7 +796,9 @@ 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 binfmt_namespace *ns = >> + binfmt_ns(file_dentry(file)->d_sb->s_user_ns); >> + char *s = ns->enabled ? "enabled\n" : "disabled\n"; >> >> return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s)); >> } >> @@ -780,25 +806,28 @@ 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 binfmt_namespace *ns; >> int res = parse_command(buffer, count); >> struct dentry *root; >> >> + ns = binfmt_ns(file_dentry(file)->d_sb->s_user_ns); >> switch (res) { >> case 1: >> /* Disable all handlers. */ >> - enabled = 0; >> + ns->enabled = 0; >> break; >> case 2: >> /* Enable all handlers. */ >> - enabled = 1; >> + 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->entries)) >> + kill_node(ns, list_first_entry(&ns->entries, >> + Node, list)); >> >> inode_unlock(d_inode(root)); >> break; >> @@ -825,24 +854,53 @@ static const struct super_operations s_ops = { >> static int bm_fill_super(struct super_block *sb, struct fs_context *fc) >> { >> int err; >> + struct user_namespace *ns = sb->s_user_ns; >> static const struct tree_descr bm_files[] = { >> [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO}, >> [3] = {"register", &bm_register_operations, S_IWUSR}, >> /* last one */ {""} >> }; >> >> + /* create a new binfmt namespace >> + * if we are not in the first user namespace >> + * but the binfmt namespace is the first one >> + */ >> + if (READ_ONCE(ns->binfmt_ns) == NULL) { >> + struct binfmt_namespace *new_ns; >> + >> + new_ns = kmalloc(sizeof(struct binfmt_namespace), >> + GFP_KERNEL); >> + if (new_ns == NULL) >> + return -ENOMEM; >> + INIT_LIST_HEAD(&new_ns->entries); >> + new_ns->enabled = 1; >> + rwlock_init(&new_ns->entries_lock); >> + new_ns->bm_mnt = NULL; >> + new_ns->entry_count = 0; >> + /* ensure new_ns is completely initialized before sharing it */ >> + smp_wmb(); >> + WRITE_ONCE(ns->binfmt_ns, new_ns); >> + } >> + >> err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files); >> if (!err) >> sb->s_op = &s_ops; >> return err; >> } >> >> +static void bm_free(struct fs_context *fc) >> +{ >> + if (fc->s_fs_info) >> + put_user_ns(fc->s_fs_info); >> +} >> + >> static int bm_get_tree(struct fs_context *fc) >> { >> - return get_tree_single(fc, bm_fill_super); >> + return get_tree_keyed(fc, bm_fill_super, get_user_ns(fc->user_ns)); >> } >> >> static const struct fs_context_operations bm_context_ops = { >> + .free = bm_free, >> .get_tree = bm_get_tree, >> }; >> >> @@ -861,6 +919,7 @@ static struct file_system_type bm_fs_type = { >> .owner = THIS_MODULE, >> .name = "binfmt_misc", >> .init_fs_context = bm_init_fs_context, >> + .fs_flags = FS_USERNS_MOUNT, >> .kill_sb = kill_litter_super, >> }; >> MODULE_ALIAS_FS("binfmt_misc"); >> diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h >> index fb9f4f799554..16e6f3a97a01 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; >> @@ -86,6 +98,9 @@ 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 5235d7f49982..092b2b4d47a6 100644 >> --- a/kernel/user.c >> +++ b/kernel/user.c >> @@ -20,6 +20,17 @@ >> #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... ? >> @@ -67,6 +78,9 @@ struct user_namespace init_user_ns = { >> .keyring_name_list = LIST_HEAD_INIT(init_user_ns.keyring_name_list), >> .keyring_sem = __RWSEM_INITIALIZER(init_user_ns.keyring_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 8eadadc478f9..f42c32269e20 100644 >> --- a/kernel/user_namespace.c >> +++ b/kernel/user_namespace.c >> @@ -191,6 +191,9 @@ 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) >> + kfree(ns->binfmt_ns); >> +#endif >> retire_userns_sysctls(ns); >> key_free_user_ns(ns); >> ns_free_inum(&ns->ns); >> > > What happened with this proposal since then? > > As there is quite some delay between the feature finally hitting > upstream and a random distro-based containter host providing it to > unprivileged users, the longer we wait, the longer the pain persists > (e.g. when building cross-arch containers or when dealing with different > qemu-user-static versions...). Is there anything we can do to help with it? Hi Jan, I'm sorry, but I have no time to work on this for the moment. So, if someone else wants to address problems of this current version I will be happy (I can help a little). Thanks, Laurent