EVM: Allow runtime modification of the set of verified xattrs
Subsystems (4)
PATCH v3 1/1 EVM: Allow runtime modification of the set of verified xattrs
Sites may wish to provide additional metadata alongside files in order to make more fine-grained security decisions[1]. The security of this is enhanced if this metadata is protected, something that EVM makes possible. However, the kernel cannot know about the set of extended attributes that local admins may wish to protect, and hardcoding this policy in the kernel makes it difficult to change over time and less convenient for distributions to enable.
This patch adds a new /sys/kernel/security/evm_xattrs node, which can be read to obtain the current set of EVM-protected extended attributes or written to in order to add new entries. Extending this list will not change the validity of any existing signatures provided that the file in question does not have any of the additional extended attributes - missing xattrs are skipped when calculating the EVM hash.
[1] For instance, a package manager could install information about the package uploader in an additional extended attribute. Local LSM policy could then be associated with that extended attribute in order to restrict the privileges available to packages from less trusted uploaders.
--- Documentation/ABI/testing/evm | 11 +++ security/integrity/evm/Kconfig | 11 +++ security/integrity/evm/evm_crypto.c | 2 +- security/integrity/evm/evm_main.c | 6 +- security/integrity/evm/evm_secfs.c | 133 ++++++++++++++++++++++++++-- 5 files changed, 153 insertions(+), 10 deletions(-)
Documentation/ABI/testing/evm +11 -0
@@ -57,3 +57,14 @@ 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 <[email protected]> +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.
security/integrity/evm/Kconfig +11 -0
@@ -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
security/integrity/evm/evm_crypto.c +1 -1
@@ -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 )
security/integrity/evm/evm_main.c +3 -3
@@ -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
@@ -98,7 +98,7 @@ 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 )
@@ -225,7 +225,7 @@ 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 ;
security/integrity/evm/evm_secfs.c +127 -6
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2.17.0.441.gb46fe60e1d-goog