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Thu, 7 Jul 2022 14:48:04 +0000 (GMT) From: Stefan Berger To: linux-integrity@vger.kernel.org Cc: zohar@linux.ibm.com, serge@hallyn.com, christian.brauner@ubuntu.com, containers@lists.linux.dev, dmitry.kasatkin@gmail.com, ebiederm@xmission.com, krzysztof.struczynski@huawei.com, roberto.sassu@huawei.com, mpeters@redhat.com, lhinds@redhat.com, lsturman@redhat.com, puiterwi@redhat.com, jejb@linux.ibm.com, jamjoom@us.ibm.com, linux-kernel@vger.kernel.org, paul@paul-moore.com, rgb@redhat.com, linux-security-module@vger.kernel.org, jmorris@namei.org, jpenumak@redhat.com, Stefan Berger , Christian Brauner , James Bottomley Subject: [PATCH v13 02/26] securityfs: Extend securityfs with namespacing support Date: Thu, 7 Jul 2022 10:47:36 -0400 Message-Id: <20220707144800.828288-3-stefanb@linux.ibm.com> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220707144800.828288-1-stefanb@linux.ibm.com> References: <20220707144800.828288-1-stefanb@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: F5w-bFtnwPXcafim-v8q7x_t36PE3msM X-Proofpoint-ORIG-GUID: Xkryqe1D2JxW80rhOQAEbihKmoOSOCtx X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.883,Hydra:6.0.517,FMLib:17.11.122.1 definitions=2022-07-07_12,2022-06-28_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 phishscore=0 mlxlogscore=999 lowpriorityscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 impostorscore=0 spamscore=0 clxscore=1015 adultscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2206140000 definitions=main-2207070057 Precedence: bulk List-ID: Enable multiple instances of securityfs by keying each instance with a pointer to the user namespace it belongs to. Since we do not need the pinning of the filesystem for the virtualization case, limit the usage of simple_pin_fs() and simpe_release_fs() to the case when the init_user_ns is active. This simplifies the cleanup for the virtualization case where usage of securityfs_remove() to free dentries is therefore not needed anymore. For the initial securityfs, i.e. the one mounted in the host userns mount, nothing changes. The rules for securityfs_remove() are as before and it is still paired with securityfs_create(). Specifically, a file created via securityfs_create_dentry() in the initial securityfs mount still needs to be removed by a call to securityfs_remove(). Creating a new dentry in the initial securityfs mount still pins the filesystem like it always did. Consequently, the initial securityfs mount is not destroyed on umount/shutdown as long as at least one user of it still has dentries that it hasn't removed with a call to securityfs_remove(). Prevent mounting of an instance of securityfs in another user namespace than it belongs to. Also, prevent accesses to files and directories by a user namespace that is neither the user namespace it belongs to nor an ancestor of the user namespace that the instance of securityfs belongs to. Do not prevent access if securityfs was bind-mounted and therefore the init_user_ns is the owning user namespace. Suggested-by: Christian Brauner Signed-off-by: Stefan Berger Signed-off-by: James Bottomley Acked-by: Serge Hallyn --- v13: - Clarified bind-mount comment following Serge's suggestion v11: - Formatted comment's first line to be '/*' --- security/inode.c | 74 +++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 63 insertions(+), 11 deletions(-) diff --git a/security/inode.c b/security/inode.c index 13e6780c4444..c7273fdbca4c 100644 --- a/security/inode.c +++ b/security/inode.c @@ -21,9 +21,39 @@ #include #include #include +#include -static struct vfsmount *mount; -static int mount_count; +static struct vfsmount *init_securityfs_mount; +static int init_securityfs_mount_count; + +static int securityfs_permission(struct user_namespace *mnt_userns, + struct inode *inode, int mask) +{ + int err; + + err = generic_permission(&init_user_ns, inode, mask); + if (!err) { + /* + * Unless securityfs has been bind-mounted from init_user_ns + * into a child user_ns container, deny access if + * current_user_ns() is not ancestor. + */ + if (inode->i_sb->s_user_ns != &init_user_ns && + !in_userns(current_user_ns(), inode->i_sb->s_user_ns)) + err = -EACCES; + } + + return err; +} + +static const struct inode_operations securityfs_dir_inode_operations = { + .permission = securityfs_permission, + .lookup = simple_lookup, +}; + +static const struct inode_operations securityfs_file_inode_operations = { + .permission = securityfs_permission, +}; static void securityfs_free_inode(struct inode *inode) { @@ -40,20 +70,25 @@ static const struct super_operations securityfs_super_operations = { static int securityfs_fill_super(struct super_block *sb, struct fs_context *fc) { static const struct tree_descr files[] = {{""}}; + struct user_namespace *ns = fc->user_ns; int error; + if (WARN_ON(ns != current_user_ns())) + return -EINVAL; + error = simple_fill_super(sb, SECURITYFS_MAGIC, files); if (error) return error; sb->s_op = &securityfs_super_operations; + sb->s_root->d_inode->i_op = &securityfs_dir_inode_operations; return 0; } static int securityfs_get_tree(struct fs_context *fc) { - return get_tree_single(fc, securityfs_fill_super); + return get_tree_keyed(fc, securityfs_fill_super, fc->user_ns); } static const struct fs_context_operations securityfs_context_ops = { @@ -71,6 +106,7 @@ static struct file_system_type fs_type = { .name = "securityfs", .init_fs_context = securityfs_init_fs_context, .kill_sb = kill_litter_super, + .fs_flags = FS_USERNS_MOUNT, }; /** @@ -109,6 +145,7 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode, const struct file_operations *fops, const struct inode_operations *iops) { + struct user_namespace *ns = current_user_ns(); struct dentry *dentry; struct inode *dir, *inode; int error; @@ -118,12 +155,19 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode, pr_debug("securityfs: creating file '%s'\n",name); - error = simple_pin_fs(&fs_type, &mount, &mount_count); - if (error) - return ERR_PTR(error); + if (ns == &init_user_ns) { + error = simple_pin_fs(&fs_type, &init_securityfs_mount, + &init_securityfs_mount_count); + if (error) + return ERR_PTR(error); + } - if (!parent) - parent = mount->mnt_root; + if (!parent) { + if (ns == &init_user_ns) + parent = init_securityfs_mount->mnt_root; + else + return ERR_PTR(-EINVAL); + } dir = d_inode(parent); @@ -148,7 +192,7 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode, inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode); inode->i_private = data; if (S_ISDIR(mode)) { - inode->i_op = &simple_dir_inode_operations; + inode->i_op = &securityfs_dir_inode_operations; inode->i_fop = &simple_dir_operations; inc_nlink(inode); inc_nlink(dir); @@ -156,6 +200,7 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode, inode->i_op = iops ? iops : &simple_symlink_inode_operations; inode->i_link = data; } else { + inode->i_op = &securityfs_file_inode_operations; inode->i_fop = fops; } d_instantiate(dentry, inode); @@ -167,7 +212,9 @@ static struct dentry *securityfs_create_dentry(const char *name, umode_t mode, dentry = ERR_PTR(error); out: inode_unlock(dir); - simple_release_fs(&mount, &mount_count); + if (ns == &init_user_ns) + simple_release_fs(&init_securityfs_mount, + &init_securityfs_mount_count); return dentry; } @@ -293,11 +340,14 @@ EXPORT_SYMBOL_GPL(securityfs_create_symlink); */ void securityfs_remove(struct dentry *dentry) { + struct user_namespace *ns; struct inode *dir; if (!dentry || IS_ERR(dentry)) return; + ns = dentry->d_sb->s_user_ns; + dir = d_inode(dentry->d_parent); inode_lock(dir); if (simple_positive(dentry)) { @@ -310,7 +360,9 @@ void securityfs_remove(struct dentry *dentry) dput(dentry); } inode_unlock(dir); - simple_release_fs(&mount, &mount_count); + if (ns == &init_user_ns) + simple_release_fs(&init_securityfs_mount, + &init_securityfs_mount_count); } EXPORT_SYMBOL_GPL(securityfs_remove);