[V5,3/3] EVM: Allow runtime modification of the set of verified xattrs

Message ID	20180511231236.5501-3-mjg59@google.com (mailing list archive)
State	New, archived
Headers	show Return-Path: <linux-integrity-owner@kernel.org> MIME-Version: 1.0 Date: Fri, 11 May 2018 16:12:36 -0700 In-Reply-To: <20180511231236.5501-1-mjg59@google.com> Message-Id: <20180511231236.5501-3-mjg59@google.com> References: <20180511231236.5501-1-mjg59@google.com> Subject: [PATCH V5 3/3] EVM: Allow runtime modification of the set of verified xattrs From: Matthew Garrett <mjg59@google.com> To: linux-integrity@vger.kernel.org Cc: zohar@linux.vnet.ibm.com, Matthew Garrett <mjg59@google.com> Content-Type: text/plain; charset="UTF-8" Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk

diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm index d12cb2eae9ee..fa31df7fd30b 100644 --- a/Documentation/ABI/testing/evm +++ b/Documentation/ABI/testing/evm @@ -57,3 +57,16 @@ Description: dracut (via 97masterkey and 98integrity) and systemd (via core/ima-setup) have support for loading keys at boot time. + +What: security/evm_xattrs +Date: April 2018 +Contact: Matthew Garrett <mjg59@google.com> +Description: + Shows the set of extended attributes used to calculate or + validate the EVM signature, and allows additional attributes + to be added at runtime. Any signatures generated after + additional attributes are added (and on files posessing those + additional attributes) will only be valid if the same + additional attributes are configured on system boot. Writing + a single period (.) will lock the xattr list from any further + modification. diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h index 4e61a9e05132..65d9293f1fb8 100644 --- a/include/uapi/linux/audit.h +++ b/include/uapi/linux/audit.h @@ -147,6 +147,7 @@ #define AUDIT_INTEGRITY_HASH 1803 /* Integrity HASH type */ #define AUDIT_INTEGRITY_PCR 1804 /* PCR invalidation msgs */ #define AUDIT_INTEGRITY_RULE 1805 /* policy rule */ +#define AUDIT_INTEGRITY_EVM_XATTR 1806 /* New EVM-covered xattr */ #define AUDIT_KERNEL 2000 /* Asynchronous audit record. NOT A REQUEST. */ diff --git a/security/integrity/evm/Kconfig b/security/integrity/evm/Kconfig index e825e0ae78e7..54adb3f9ad1d 100644 --- a/security/integrity/evm/Kconfig +++ b/security/integrity/evm/Kconfig @@ -42,6 +42,17 @@ config EVM_EXTRA_SMACK_XATTRS additional info to the calculation, requires existing EVM labeled file systems to be relabeled. +config EVM_ADD_XATTRS + bool "Add additional EVM extended attributes at runtime" + depends on EVM + default n + help + Allow userland to provide additional xattrs for HMAC calculation. + + When this option is enabled, root can add additional xattrs to the + list used by EVM by writing them into + /sys/kernel/security/evm_xattrs. + config EVM_LOAD_X509 bool "Load an X509 certificate onto the '.evm' trusted keyring" depends on EVM && INTEGRITY_TRUSTED_KEYRING diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c index caeea20670cc..494da5fcc092 100644 --- a/security/integrity/evm/evm_crypto.c +++ b/security/integrity/evm/evm_crypto.c @@ -208,7 +208,7 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry, return PTR_ERR(desc); error = -ENODATA; - list_for_each_entry(xattr, &evm_config_xattrnames, list) { + list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { bool is_ima = false; if (strcmp(xattr->name, XATTR_NAME_IMA) == 0) diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index 09582d4fc4a8..f9eff5041e4c 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -35,7 +35,7 @@ static const char * const integrity_status_msg[] = { }; int evm_hmac_attrs; -static struct xattr_list evm_config_default_xattrnames[] __ro_after_init = { +static struct xattr_list evm_config_default_xattrnames[] = { #ifdef CONFIG_SECURITY_SELINUX {.name = XATTR_NAME_SELINUX}, #endif @@ -101,7 +101,7 @@ static int evm_find_protected_xattrs(struct dentry *dentry) if (!(inode->i_opflags & IOP_XATTR)) return -EOPNOTSUPP; - list_for_each_entry(xattr, &evm_config_xattrnames, list) { + list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0); if (error < 0) { if (error == -ENODATA) @@ -228,7 +228,7 @@ static int evm_protected_xattr(const char *req_xattr_name) struct xattr_list *xattr; namelen = strlen(req_xattr_name); - list_for_each_entry(xattr, &evm_config_xattrnames, list) { + list_for_each_entry_rcu(xattr, &evm_config_xattrnames, list) { if ((strlen(xattr->name) == namelen) && (strncmp(req_xattr_name, xattr->name, namelen) == 0)) { found = 1; diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c index e44380f0cb45..97e975d91241 100644 --- a/security/integrity/evm/evm_secfs.c +++ b/security/integrity/evm/evm_secfs.c @@ -15,14 +15,22 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt +#include <linux/audit.h> #include <linux/uaccess.h> #include <linux/module.h> +#include <linux/mutex.h> #include "evm.h" static struct dentry *evm_dir; static struct dentry *evm_init_tpm; static struct dentry *evm_symlink; +#ifdef CONFIG_EVM_ADD_XATTRS +static struct dentry *evm_xattrs; +static DEFINE_MUTEX(xattr_list_mutex); +static int evm_xattrs_locked; +#endif + /** * evm_read_key - read() for <securityfs>/evm * @@ -109,6 +117,166 @@ static const struct file_operations evm_key_ops = { .write = evm_write_key, }; +#ifdef CONFIG_EVM_ADD_XATTRS +/** + * evm_read_xattrs - read() for <securityfs>/evm_xattrs + * + * @filp: file pointer, not actually used + * @buf: where to put the result + * @count: maximum to send along + * @ppos: where to start + * + * Returns number of bytes read or error code, as appropriate + */ +static ssize_t evm_read_xattrs(struct file *filp, char __user *buf, + size_t count, loff_t *ppos) +{ + char *temp; + int offset = 0; + ssize_t rc, size = 0; + struct xattr_list *xattr; + + if (*ppos != 0) + return 0; + + rc = mutex_lock_interruptible(&xattr_list_mutex); + if (rc) + return -ERESTARTSYS; + + list_for_each_entry(xattr, &evm_config_xattrnames, list) + size += strlen(xattr->name) + 1; + + temp = kmalloc(size + 1, GFP_KERNEL); + if (!temp) + return -ENOMEM; + + list_for_each_entry(xattr, &evm_config_xattrnames, list) { + sprintf(temp + offset, "%s\n", xattr->name); + offset += strlen(xattr->name) + 1; + } + + mutex_unlock(&xattr_list_mutex); + rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp)); + + return rc; +} + +/** + * evm_write_xattrs - write() for <securityfs>/evm_xattrs + * @file: file pointer, not actually used + * @buf: where to get the data from + * @count: bytes sent + * @ppos: where to start + * + * Returns number of bytes written or error code, as appropriate + */ +static ssize_t evm_write_xattrs(struct file *file, const char __user *buf, + size_t count, loff_t *ppos) +{ + int len, err; + struct xattr_list *xattr, *tmp; + struct audit_buffer *ab; + struct iattr newattrs; + struct inode *inode; + + if (!capable(CAP_SYS_ADMIN) || evm_xattrs_locked) + return -EPERM; + + if (*ppos != 0) + return -EINVAL; + + if (count > XATTR_NAME_MAX) + return -E2BIG; + + ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_EVM_XATTR); + if (IS_ERR(ab)) + return PTR_ERR(ab); + + xattr = kmalloc(sizeof(struct xattr_list), GFP_KERNEL); + if (!xattr) { + err = -ENOMEM; + goto out; + } + + xattr->name = memdup_user_nul(buf, count); + if (IS_ERR(xattr->name)) { + err = PTR_ERR(xattr->name); + xattr->name = NULL; + goto out; + } + + /* Remove any trailing newline */ + len = strlen(xattr->name); + if (xattr->name[len-1] == '\n') + xattr->name[len-1] = '\0'; + + if (strcmp(xattr->name, ".") == 0) { + evm_xattrs_locked = 1; + inode = evm_xattrs->d_inode; + inode_lock(inode); + newattrs.ia_mode = S_IFREG | 0440; + newattrs.ia_valid = ATTR_MODE; + err = notify_change(evm_xattrs, &newattrs, NULL); + inode_unlock(inode); + audit_log_format(ab, "locked"); + if (!err) + err = count; + goto out; + } + + audit_log_format(ab, "xattr="); + audit_log_untrustedstring(ab, xattr->name); + + if (strncmp(xattr->name, XATTR_SECURITY_PREFIX, + XATTR_SECURITY_PREFIX_LEN) != 0) { + err = -EINVAL; + goto out; + } + + /* Guard against races in evm_read_xattrs */ + mutex_lock(&xattr_list_mutex); + list_for_each_entry(tmp, &evm_config_xattrnames, list) { + if (strcmp(xattr->name, tmp->name) == 0) { + err = -EEXIST; + mutex_unlock(&xattr_list_mutex); + goto out; + } + } + list_add_tail_rcu(&xattr->list, &evm_config_xattrnames); + mutex_unlock(&xattr_list_mutex); + + audit_log_format(ab, " res=0"); + audit_log_end(ab); + return count; +out: + audit_log_format(ab, " res=%d", err); + audit_log_end(ab); + kfree(xattr->name); + kfree(xattr); + return err; +} + +static const struct file_operations evm_xattr_ops = { + .read = evm_read_xattrs, + .write = evm_write_xattrs, +}; + +static int evm_init_xattrs(void) +{ + evm_xattrs = securityfs_create_file("evm_xattrs", 0660, evm_dir, NULL, + &evm_xattr_ops); + if (!evm_xattrs || IS_ERR(evm_xattrs)) + return -EFAULT; + + return 0; +} +#else +static int evm_init_xattrs(void) +{ + return 0; +} +#endif + int __init evm_init_secfs(void) { int error = 0; @@ -131,6 +299,11 @@ int __init evm_init_secfs(void) goto out; } + if (evm_init_xattrs() != 0) { + error = -EFAULT; + goto out; + } + return 0; out: securityfs_remove(evm_symlink);

[V5,3/3] EVM: Allow runtime modification of the set of verified xattrs

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