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linux-bl808/security/integrity/evm/evm_main.c
Christian Brauner e61b135f7b
integrity: implement get and set acl hook 
The current way of setting and getting posix acls through the generic
xattr interface is error prone and type unsafe. The vfs needs to
interpret and fixup posix acls before storing or reporting it to
userspace. Various hacks exist to make this work. The code is hard to
understand and difficult to maintain in it's current form. Instead of
making this work by hacking posix acls through xattr handlers we are
building a dedicated posix acl api around the get and set inode
operations. This removes a lot of hackiness and makes the codepaths
easier to maintain. A lot of background can be found in [1].

So far posix acls were passed as a void blob to the security and
integrity modules. Some of them like evm then proceed to interpret the
void pointer and convert it into the kernel internal struct posix acl
representation to perform their integrity checking magic. This is
obviously pretty problematic as that requires knowledge that only the
vfs is guaranteed to have and has lead to various bugs. Add a proper
security hook for setting posix acls and pass down the posix acls in
their appropriate vfs format instead of hacking it through a void
pointer stored in the uapi format.

I spent considerate time in the security module and integrity
infrastructure and audited all codepaths. EVM is the only part that
really has restrictions based on the actual posix acl values passed
through it (e.g., i_mode). Before this dedicated hook EVM used to translate
from the uapi posix acl format sent to it in the form of a void pointer
into the vfs format. This is not a good thing. Instead of hacking around in
the uapi struct give EVM the posix acls in the appropriate vfs format and
perform sane permissions checks that mirror what it used to to in the
generic xattr hook.

IMA doesn't have any restrictions on posix acls. When posix acls are
changed it just wants to update its appraisal status to trigger an EVM
revalidation.

The removal of posix acls is equivalent to passing NULL to the posix set
acl hooks. This is the same as before through the generic xattr api.

Link: https://lore.kernel.org/all/20220801145520.1532837-1-brauner@kernel.org [1]
Acked-by: Paul Moore <paul@paul-moore.com> (LSM)
Signed-off-by: Christian Brauner (Microsoft) <brauner@kernel.org>
2022-10-20 10:13:29 +02:00

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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2005-2010 IBM Corporation
*
* Author:
* Mimi Zohar <zohar@us.ibm.com>
* Kylene Hall <kjhall@us.ibm.com>
*
* File: evm_main.c
* implements evm_inode_setxattr, evm_inode_post_setxattr,
* evm_inode_removexattr, evm_verifyxattr, and evm_inode_set_acl.
*/
#define pr_fmt(fmt) "EVM: "fmt
#include <linux/init.h>
#include <linux/crypto.h>
#include <linux/audit.h>
#include <linux/xattr.h>
#include <linux/integrity.h>
#include <linux/evm.h>
#include <linux/magic.h>
#include <linux/posix_acl_xattr.h>
#include <crypto/hash.h>
#include <crypto/hash_info.h>
#include <crypto/algapi.h>
#include "evm.h"
int evm_initialized;
static const char * const integrity_status_msg[] = {
"pass", "pass_immutable", "fail", "fail_immutable", "no_label",
"no_xattrs", "unknown"
};
int evm_hmac_attrs;
static struct xattr_list evm_config_default_xattrnames[] = {
{
.name = XATTR_NAME_SELINUX,
.enabled = IS_ENABLED(CONFIG_SECURITY_SELINUX)
},
{
.name = XATTR_NAME_SMACK,
.enabled = IS_ENABLED(CONFIG_SECURITY_SMACK)
},
{
.name = XATTR_NAME_SMACKEXEC,
.enabled = IS_ENABLED(CONFIG_EVM_EXTRA_SMACK_XATTRS)
},
{
.name = XATTR_NAME_SMACKTRANSMUTE,
.enabled = IS_ENABLED(CONFIG_EVM_EXTRA_SMACK_XATTRS)
},
{
.name = XATTR_NAME_SMACKMMAP,
.enabled = IS_ENABLED(CONFIG_EVM_EXTRA_SMACK_XATTRS)
},
{
.name = XATTR_NAME_APPARMOR,
.enabled = IS_ENABLED(CONFIG_SECURITY_APPARMOR)
},
{
.name = XATTR_NAME_IMA,
.enabled = IS_ENABLED(CONFIG_IMA_APPRAISE)
},
{
.name = XATTR_NAME_CAPS,
.enabled = true
},
};
LIST_HEAD(evm_config_xattrnames);
static int evm_fixmode __ro_after_init;
static int __init evm_set_fixmode(char *str)
{
if (strncmp(str, "fix", 3) == 0)
evm_fixmode = 1;
else
pr_err("invalid \"%s\" mode", str);
return 1;
}
__setup("evm=", evm_set_fixmode);
static void __init evm_init_config(void)
{
int i, xattrs;
xattrs = ARRAY_SIZE(evm_config_default_xattrnames);
pr_info("Initialising EVM extended attributes:\n");
for (i = 0; i < xattrs; i++) {
pr_info("%s%s\n", evm_config_default_xattrnames[i].name,
!evm_config_default_xattrnames[i].enabled ?
" (disabled)" : "");
list_add_tail(&evm_config_default_xattrnames[i].list,
&evm_config_xattrnames);
}
#ifdef CONFIG_EVM_ATTR_FSUUID
evm_hmac_attrs |= EVM_ATTR_FSUUID;
#endif
pr_info("HMAC attrs: 0x%x\n", evm_hmac_attrs);
}
static bool evm_key_loaded(void)
{
return (bool)(evm_initialized & EVM_KEY_MASK);
}
/*
* This function determines whether or not it is safe to ignore verification
* errors, based on the ability of EVM to calculate HMACs. If the HMAC key
* is not loaded, and it cannot be loaded in the future due to the
* EVM_SETUP_COMPLETE initialization flag, allowing an operation despite the
* attrs/xattrs being found invalid will not make them valid.
*/
static bool evm_hmac_disabled(void)
{
if (evm_initialized & EVM_INIT_HMAC)
return false;
if (!(evm_initialized & EVM_SETUP_COMPLETE))
return false;
return true;
}
static int evm_find_protected_xattrs(struct dentry *dentry)
{
struct inode *inode = d_backing_inode(dentry);
struct xattr_list *xattr;
int error;
int count = 0;
if (!(inode->i_opflags & IOP_XATTR))
return -EOPNOTSUPP;
list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
error = __vfs_getxattr(dentry, inode, xattr->name, NULL, 0);
if (error < 0) {
if (error == -ENODATA)
continue;
return error;
}
count++;
}
return count;
}
/*
* evm_verify_hmac - calculate and compare the HMAC with the EVM xattr
*
* Compute the HMAC on the dentry's protected set of extended attributes
* and compare it against the stored security.evm xattr.
*
* For performance:
* - use the previoulsy retrieved xattr value and length to calculate the
* HMAC.)
* - cache the verification result in the iint, when available.
*
* Returns integrity status
*/
static enum integrity_status evm_verify_hmac(struct dentry *dentry,
const char *xattr_name,
char *xattr_value,
size_t xattr_value_len,
struct integrity_iint_cache *iint)
{
struct evm_ima_xattr_data *xattr_data = NULL;
struct signature_v2_hdr *hdr;
enum integrity_status evm_status = INTEGRITY_PASS;
struct evm_digest digest;
struct inode *inode;
int rc, xattr_len, evm_immutable = 0;
if (iint && (iint->evm_status == INTEGRITY_PASS ||
iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
return iint->evm_status;
/* if status is not PASS, try to check again - against -ENOMEM */
/* first need to know the sig type */
rc = vfs_getxattr_alloc(&init_user_ns, dentry, XATTR_NAME_EVM,
(char **)&xattr_data, 0, GFP_NOFS);
if (rc <= 0) {
evm_status = INTEGRITY_FAIL;
if (rc == -ENODATA) {
rc = evm_find_protected_xattrs(dentry);
if (rc > 0)
evm_status = INTEGRITY_NOLABEL;
else if (rc == 0)
evm_status = INTEGRITY_NOXATTRS; /* new file */
} else if (rc == -EOPNOTSUPP) {
evm_status = INTEGRITY_UNKNOWN;
}
goto out;
}
xattr_len = rc;
/* check value type */
switch (xattr_data->type) {
case EVM_XATTR_HMAC:
if (xattr_len != sizeof(struct evm_xattr)) {
evm_status = INTEGRITY_FAIL;
goto out;
}
digest.hdr.algo = HASH_ALGO_SHA1;
rc = evm_calc_hmac(dentry, xattr_name, xattr_value,
xattr_value_len, &digest);
if (rc)
break;
rc = crypto_memneq(xattr_data->data, digest.digest,
SHA1_DIGEST_SIZE);
if (rc)
rc = -EINVAL;
break;
case EVM_XATTR_PORTABLE_DIGSIG:
evm_immutable = 1;
fallthrough;
case EVM_IMA_XATTR_DIGSIG:
/* accept xattr with non-empty signature field */
if (xattr_len <= sizeof(struct signature_v2_hdr)) {
evm_status = INTEGRITY_FAIL;
goto out;
}
hdr = (struct signature_v2_hdr *)xattr_data;
digest.hdr.algo = hdr->hash_algo;
rc = evm_calc_hash(dentry, xattr_name, xattr_value,
xattr_value_len, xattr_data->type, &digest);
if (rc)
break;
rc = integrity_digsig_verify(INTEGRITY_KEYRING_EVM,
(const char *)xattr_data, xattr_len,
digest.digest, digest.hdr.length);
if (!rc) {
inode = d_backing_inode(dentry);
if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
if (iint)
iint->flags |= EVM_IMMUTABLE_DIGSIG;
evm_status = INTEGRITY_PASS_IMMUTABLE;
} else if (!IS_RDONLY(inode) &&
!(inode->i_sb->s_readonly_remount) &&
!IS_IMMUTABLE(inode)) {
evm_update_evmxattr(dentry, xattr_name,
xattr_value,
xattr_value_len);
}
}
break;
default:
rc = -EINVAL;
break;
}
if (rc) {
if (rc == -ENODATA)
evm_status = INTEGRITY_NOXATTRS;
else if (evm_immutable)
evm_status = INTEGRITY_FAIL_IMMUTABLE;
else
evm_status = INTEGRITY_FAIL;
}
pr_debug("digest: (%d) [%*phN]\n", digest.hdr.length, digest.hdr.length,
digest.digest);
out:
if (iint)
iint->evm_status = evm_status;
kfree(xattr_data);
return evm_status;
}
static int evm_protected_xattr_common(const char *req_xattr_name,
bool all_xattrs)
{
int namelen;
int found = 0;
struct xattr_list *xattr;
namelen = strlen(req_xattr_name);
list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
if (!all_xattrs && !xattr->enabled)
continue;
if ((strlen(xattr->name) == namelen)
&& (strncmp(req_xattr_name, xattr->name, namelen) == 0)) {
found = 1;
break;
}
if (strncmp(req_xattr_name,
xattr->name + XATTR_SECURITY_PREFIX_LEN,
strlen(req_xattr_name)) == 0) {
found = 1;
break;
}
}
return found;
}
static int evm_protected_xattr(const char *req_xattr_name)
{
return evm_protected_xattr_common(req_xattr_name, false);
}
int evm_protected_xattr_if_enabled(const char *req_xattr_name)
{
return evm_protected_xattr_common(req_xattr_name, true);
}
/**
* evm_read_protected_xattrs - read EVM protected xattr names, lengths, values
* @dentry: dentry of the read xattrs
* @inode: inode of the read xattrs
* @buffer: buffer xattr names, lengths or values are copied to
* @buffer_size: size of buffer
* @type: n: names, l: lengths, v: values
* @canonical_fmt: data format (true: little endian, false: native format)
*
* Read protected xattr names (separated by |), lengths (u32) or values for a
* given dentry and return the total size of copied data. If buffer is NULL,
* just return the total size.
*
* Returns the total size on success, a negative value on error.
*/
int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
int buffer_size, char type, bool canonical_fmt)
{
struct xattr_list *xattr;
int rc, size, total_size = 0;
list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
rc = __vfs_getxattr(dentry, d_backing_inode(dentry),
xattr->name, NULL, 0);
if (rc < 0 && rc == -ENODATA)
continue;
else if (rc < 0)
return rc;
switch (type) {
case 'n':
size = strlen(xattr->name) + 1;
if (buffer) {
if (total_size)
*(buffer + total_size - 1) = '|';
memcpy(buffer + total_size, xattr->name, size);
}
break;
case 'l':
size = sizeof(u32);
if (buffer) {
if (canonical_fmt)
rc = (__force int)cpu_to_le32(rc);
*(u32 *)(buffer + total_size) = rc;
}
break;
case 'v':
size = rc;
if (buffer) {
rc = __vfs_getxattr(dentry,
d_backing_inode(dentry), xattr->name,
buffer + total_size,
buffer_size - total_size);
if (rc < 0)
return rc;
}
break;
default:
return -EINVAL;
}
total_size += size;
}
return total_size;
}
/**
* evm_verifyxattr - verify the integrity of the requested xattr
* @dentry: object of the verify xattr
* @xattr_name: requested xattr
* @xattr_value: requested xattr value
* @xattr_value_len: requested xattr value length
*
* Calculate the HMAC for the given dentry and verify it against the stored
* security.evm xattr. For performance, use the xattr value and length
* previously retrieved to calculate the HMAC.
*
* Returns the xattr integrity status.
*
* This function requires the caller to lock the inode's i_mutex before it
* is executed.
*/
enum integrity_status evm_verifyxattr(struct dentry *dentry,
const char *xattr_name,
void *xattr_value, size_t xattr_value_len,
struct integrity_iint_cache *iint)
{
if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
return INTEGRITY_UNKNOWN;
if (!iint) {
iint = integrity_iint_find(d_backing_inode(dentry));
if (!iint)
return INTEGRITY_UNKNOWN;
}
return evm_verify_hmac(dentry, xattr_name, xattr_value,
xattr_value_len, iint);
}
EXPORT_SYMBOL_GPL(evm_verifyxattr);
/*
* evm_verify_current_integrity - verify the dentry's metadata integrity
* @dentry: pointer to the affected dentry
*
* Verify and return the dentry's metadata integrity. The exceptions are
* before EVM is initialized or in 'fix' mode.
*/
static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)
{
struct inode *inode = d_backing_inode(dentry);
if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
return INTEGRITY_PASS;
return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
}
/*
* evm_xattr_acl_change - check if passed ACL changes the inode mode
* @mnt_userns: user namespace of the idmapped mount
* @dentry: pointer to the affected dentry
* @xattr_name: requested xattr
* @xattr_value: requested xattr value
* @xattr_value_len: requested xattr value length
*
* Check if passed ACL changes the inode mode, which is protected by EVM.
*
* Returns 1 if passed ACL causes inode mode change, 0 otherwise.
*/
static int evm_xattr_acl_change(struct user_namespace *mnt_userns,
struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
{
#ifdef CONFIG_FS_POSIX_ACL
umode_t mode;
struct posix_acl *acl = NULL, *acl_res;
struct inode *inode = d_backing_inode(dentry);
int rc;
/*
* An earlier comment here mentioned that the idmappings for
* ACL_{GROUP,USER} don't matter since EVM is only interested in the
* mode stored as part of POSIX ACLs. Nonetheless, if it must translate
* from the uapi POSIX ACL representation to the VFS internal POSIX ACL
* representation it should do so correctly. There's no guarantee that
* we won't change POSIX ACLs in a way that ACL_{GROUP,USER} matters
* for the mode at some point and it's difficult to keep track of all
* the LSM and integrity modules and what they do to POSIX ACLs.
*
* Frankly, EVM shouldn't try to interpret the uapi struct for POSIX
* ACLs it received. It requires knowledge that only the VFS is
* guaranteed to have.
*/
acl = vfs_set_acl_prepare(mnt_userns, i_user_ns(inode),
xattr_value, xattr_value_len);
if (IS_ERR_OR_NULL(acl))
return 1;
acl_res = acl;
/*
* Passing mnt_userns is necessary to correctly determine the GID in
* an idmapped mount, as the GID is used to clear the setgid bit in
* the inode mode.
*/
rc = posix_acl_update_mode(mnt_userns, inode, &mode, &acl_res);
posix_acl_release(acl);
if (rc)
return 1;
if (inode->i_mode != mode)
return 1;
#endif
return 0;
}
/*
* evm_xattr_change - check if passed xattr value differs from current value
* @mnt_userns: user namespace of the idmapped mount
* @dentry: pointer to the affected dentry
* @xattr_name: requested xattr
* @xattr_value: requested xattr value
* @xattr_value_len: requested xattr value length
*
* Check if passed xattr value differs from current value.
*
* Returns 1 if passed xattr value differs from current value, 0 otherwise.
*/
static int evm_xattr_change(struct user_namespace *mnt_userns,
struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
{
char *xattr_data = NULL;
int rc = 0;
if (posix_xattr_acl(xattr_name))
return evm_xattr_acl_change(mnt_userns, dentry, xattr_name,
xattr_value, xattr_value_len);
rc = vfs_getxattr_alloc(&init_user_ns, dentry, xattr_name, &xattr_data,
0, GFP_NOFS);
if (rc < 0)
return 1;
if (rc == xattr_value_len)
rc = !!memcmp(xattr_value, xattr_data, rc);
else
rc = 1;
kfree(xattr_data);
return rc;
}
/*
* evm_protect_xattr - protect the EVM extended attribute
*
* Prevent security.evm from being modified or removed without the
* necessary permissions or when the existing value is invalid.
*
* The posix xattr acls are 'system' prefixed, which normally would not
* affect security.evm. An interesting side affect of writing posix xattr
* acls is their modifying of the i_mode, which is included in security.evm.
* For posix xattr acls only, permit security.evm, even if it currently
* doesn't exist, to be updated unless the EVM signature is immutable.
*/
static int evm_protect_xattr(struct user_namespace *mnt_userns,
struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
{
enum integrity_status evm_status;
if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
} else if (!evm_protected_xattr(xattr_name)) {
if (!posix_xattr_acl(xattr_name))
return 0;
evm_status = evm_verify_current_integrity(dentry);
if ((evm_status == INTEGRITY_PASS) ||
(evm_status == INTEGRITY_NOXATTRS))
return 0;
goto out;
}
evm_status = evm_verify_current_integrity(dentry);
if (evm_status == INTEGRITY_NOXATTRS) {
struct integrity_iint_cache *iint;
/* Exception if the HMAC is not going to be calculated. */
if (evm_hmac_disabled())
return 0;
iint = integrity_iint_find(d_backing_inode(dentry));
if (iint && (iint->flags & IMA_NEW_FILE))
return 0;
/* exception for pseudo filesystems */
if (dentry->d_sb->s_magic == TMPFS_MAGIC
|| dentry->d_sb->s_magic == SYSFS_MAGIC)
return 0;
integrity_audit_msg(AUDIT_INTEGRITY_METADATA,
dentry->d_inode, dentry->d_name.name,
"update_metadata",
integrity_status_msg[evm_status],
-EPERM, 0);
}
out:
/* Exception if the HMAC is not going to be calculated. */
if (evm_hmac_disabled() && (evm_status == INTEGRITY_NOLABEL ||
evm_status == INTEGRITY_UNKNOWN))
return 0;
/*
* Writing other xattrs is safe for portable signatures, as portable
* signatures are immutable and can never be updated.
*/
if (evm_status == INTEGRITY_FAIL_IMMUTABLE)
return 0;
if (evm_status == INTEGRITY_PASS_IMMUTABLE &&
!evm_xattr_change(mnt_userns, dentry, xattr_name, xattr_value,
xattr_value_len))
return 0;
if (evm_status != INTEGRITY_PASS &&
evm_status != INTEGRITY_PASS_IMMUTABLE)
integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
dentry->d_name.name, "appraise_metadata",
integrity_status_msg[evm_status],
-EPERM, 0);
return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
}
/**
* evm_inode_setxattr - protect the EVM extended attribute
* @mnt_userns: user namespace of the idmapped mount
* @dentry: pointer to the affected dentry
* @xattr_name: pointer to the affected extended attribute name
* @xattr_value: pointer to the new extended attribute value
* @xattr_value_len: pointer to the new extended attribute value length
*
* Before allowing the 'security.evm' protected xattr to be updated,
* verify the existing value is valid. As only the kernel should have
* access to the EVM encrypted key needed to calculate the HMAC, prevent
* userspace from writing HMAC value. Writing 'security.evm' requires
* requires CAP_SYS_ADMIN privileges.
*/
int evm_inode_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
const char *xattr_name, const void *xattr_value,
size_t xattr_value_len)
{
const struct evm_ima_xattr_data *xattr_data = xattr_value;
/* Policy permits modification of the protected xattrs even though
* there's no HMAC key loaded
*/
if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
return 0;
if (strcmp(xattr_name, XATTR_NAME_EVM) == 0) {
if (!xattr_value_len)
return -EINVAL;
if (xattr_data->type != EVM_IMA_XATTR_DIGSIG &&
xattr_data->type != EVM_XATTR_PORTABLE_DIGSIG)
return -EPERM;
}
return evm_protect_xattr(mnt_userns, dentry, xattr_name, xattr_value,
xattr_value_len);
}
/**
* evm_inode_removexattr - protect the EVM extended attribute
* @mnt_userns: user namespace of the idmapped mount
* @dentry: pointer to the affected dentry
* @xattr_name: pointer to the affected extended attribute name
*
* Removing 'security.evm' requires CAP_SYS_ADMIN privileges and that
* the current value is valid.
*/
int evm_inode_removexattr(struct user_namespace *mnt_userns,
struct dentry *dentry, const char *xattr_name)
{
/* Policy permits modification of the protected xattrs even though
* there's no HMAC key loaded
*/
if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
return 0;
return evm_protect_xattr(mnt_userns, dentry, xattr_name, NULL, 0);
}
#ifdef CONFIG_FS_POSIX_ACL
static int evm_inode_set_acl_change(struct user_namespace *mnt_userns,
struct dentry *dentry, const char *name,
struct posix_acl *kacl)
{
int rc;
umode_t mode;
struct inode *inode = d_backing_inode(dentry);
if (!kacl)
return 1;
rc = posix_acl_update_mode(mnt_userns, inode, &mode, &kacl);
if (rc || (inode->i_mode != mode))
return 1;
return 0;
}
#else
static inline int evm_inode_set_acl_change(struct user_namespace *mnt_userns,
struct dentry *dentry,
const char *name,
struct posix_acl *kacl)
{
return 0;
}
#endif
/**
* evm_inode_set_acl - protect the EVM extended attribute from posix acls
* @mnt_userns: user namespace of the idmapped mount
* @dentry: pointer to the affected dentry
* @acl_name: name of the posix acl
* @kacl: pointer to the posix acls
*
* Prevent modifying posix acls causing the EVM HMAC to be re-calculated
* and 'security.evm' xattr updated, unless the existing 'security.evm' is
* valid.
*/
int evm_inode_set_acl(struct user_namespace *mnt_userns, struct dentry *dentry,
const char *acl_name, struct posix_acl *kacl)
{
enum integrity_status evm_status;
/* Policy permits modification of the protected xattrs even though
* there's no HMAC key loaded
*/
if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
return 0;
evm_status = evm_verify_current_integrity(dentry);
if ((evm_status == INTEGRITY_PASS) ||
(evm_status == INTEGRITY_NOXATTRS))
return 0;
/* Exception if the HMAC is not going to be calculated. */
if (evm_hmac_disabled() && (evm_status == INTEGRITY_NOLABEL ||
evm_status == INTEGRITY_UNKNOWN))
return 0;
/*
* Writing other xattrs is safe for portable signatures, as portable
* signatures are immutable and can never be updated.
*/
if (evm_status == INTEGRITY_FAIL_IMMUTABLE)
return 0;
if (evm_status == INTEGRITY_PASS_IMMUTABLE &&
!evm_inode_set_acl_change(mnt_userns, dentry, acl_name, kacl))
return 0;
if (evm_status != INTEGRITY_PASS &&
evm_status != INTEGRITY_PASS_IMMUTABLE)
integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
dentry->d_name.name, "appraise_metadata",
integrity_status_msg[evm_status],
-EPERM, 0);
return evm_status == INTEGRITY_PASS ? 0 : -EPERM;
}
static void evm_reset_status(struct inode *inode)
{
struct integrity_iint_cache *iint;
iint = integrity_iint_find(inode);
if (iint)
iint->evm_status = INTEGRITY_UNKNOWN;
}
/**
* evm_revalidate_status - report whether EVM status re-validation is necessary
* @xattr_name: pointer to the affected extended attribute name
*
* Report whether callers of evm_verifyxattr() should re-validate the
* EVM status.
*
* Return true if re-validation is necessary, false otherwise.
*/
bool evm_revalidate_status(const char *xattr_name)
{
if (!evm_key_loaded())
return false;
/* evm_inode_post_setattr() passes NULL */
if (!xattr_name)
return true;
if (!evm_protected_xattr(xattr_name) && !posix_xattr_acl(xattr_name) &&
strcmp(xattr_name, XATTR_NAME_EVM))
return false;
return true;
}
/**
* evm_inode_post_setxattr - update 'security.evm' to reflect the changes
* @dentry: pointer to the affected dentry
* @xattr_name: pointer to the affected extended attribute name
* @xattr_value: pointer to the new extended attribute value
* @xattr_value_len: pointer to the new extended attribute value length
*
* Update the HMAC stored in 'security.evm' to reflect the change.
*
* No need to take the i_mutex lock here, as this function is called from
* __vfs_setxattr_noperm(). The caller of which has taken the inode's
* i_mutex lock.
*/
void evm_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
const void *xattr_value, size_t xattr_value_len)
{
if (!evm_revalidate_status(xattr_name))
return;
evm_reset_status(dentry->d_inode);
if (!strcmp(xattr_name, XATTR_NAME_EVM))
return;
if (!(evm_initialized & EVM_INIT_HMAC))
return;
evm_update_evmxattr(dentry, xattr_name, xattr_value, xattr_value_len);
}
/**
* evm_inode_post_removexattr - update 'security.evm' after removing the xattr
* @dentry: pointer to the affected dentry
* @xattr_name: pointer to the affected extended attribute name
*
* Update the HMAC stored in 'security.evm' to reflect removal of the xattr.
*
* No need to take the i_mutex lock here, as this function is called from
* vfs_removexattr() which takes the i_mutex.
*/
void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
{
if (!evm_revalidate_status(xattr_name))
return;
evm_reset_status(dentry->d_inode);
if (!strcmp(xattr_name, XATTR_NAME_EVM))
return;
if (!(evm_initialized & EVM_INIT_HMAC))
return;
evm_update_evmxattr(dentry, xattr_name, NULL, 0);
}
static int evm_attr_change(struct user_namespace *mnt_userns,
struct dentry *dentry, struct iattr *attr)
{
struct inode *inode = d_backing_inode(dentry);
unsigned int ia_valid = attr->ia_valid;
if (!i_uid_needs_update(mnt_userns, attr, inode) &&
!i_gid_needs_update(mnt_userns, attr, inode) &&
(!(ia_valid & ATTR_MODE) || attr->ia_mode == inode->i_mode))
return 0;
return 1;
}
/**
* evm_inode_setattr - prevent updating an invalid EVM extended attribute
* @dentry: pointer to the affected dentry
*
* Permit update of file attributes when files have a valid EVM signature,
* except in the case of them having an immutable portable signature.
*/
int evm_inode_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
struct iattr *attr)
{
unsigned int ia_valid = attr->ia_valid;
enum integrity_status evm_status;
/* Policy permits modification of the protected attrs even though
* there's no HMAC key loaded
*/
if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
return 0;
if (!(ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID)))
return 0;
evm_status = evm_verify_current_integrity(dentry);
/*
* Writing attrs is safe for portable signatures, as portable signatures
* are immutable and can never be updated.
*/
if ((evm_status == INTEGRITY_PASS) ||
(evm_status == INTEGRITY_NOXATTRS) ||
(evm_status == INTEGRITY_FAIL_IMMUTABLE) ||
(evm_hmac_disabled() && (evm_status == INTEGRITY_NOLABEL ||
evm_status == INTEGRITY_UNKNOWN)))
return 0;
if (evm_status == INTEGRITY_PASS_IMMUTABLE &&
!evm_attr_change(mnt_userns, dentry, attr))
return 0;
integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry),
dentry->d_name.name, "appraise_metadata",
integrity_status_msg[evm_status], -EPERM, 0);
return -EPERM;
}
/**
* evm_inode_post_setattr - update 'security.evm' after modifying metadata
* @dentry: pointer to the affected dentry
* @ia_valid: for the UID and GID status
*
* For now, update the HMAC stored in 'security.evm' to reflect UID/GID
* changes.
*
* This function is called from notify_change(), which expects the caller
* to lock the inode's i_mutex.
*/
void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
{
if (!evm_revalidate_status(NULL))
return;
evm_reset_status(dentry->d_inode);
if (!(evm_initialized & EVM_INIT_HMAC))
return;
if (ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID))
evm_update_evmxattr(dentry, NULL, NULL, 0);
}
/*
* evm_inode_init_security - initializes security.evm HMAC value
*/
int evm_inode_init_security(struct inode *inode,
const struct xattr *lsm_xattr,
struct xattr *evm_xattr)
{
struct evm_xattr *xattr_data;
int rc;
if (!(evm_initialized & EVM_INIT_HMAC) ||
!evm_protected_xattr(lsm_xattr->name))
return 0;
xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
if (!xattr_data)
return -ENOMEM;
xattr_data->data.type = EVM_XATTR_HMAC;
rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
if (rc < 0)
goto out;
evm_xattr->value = xattr_data;
evm_xattr->value_len = sizeof(*xattr_data);
evm_xattr->name = XATTR_EVM_SUFFIX;
return 0;
out:
kfree(xattr_data);
return rc;
}
EXPORT_SYMBOL_GPL(evm_inode_init_security);
#ifdef CONFIG_EVM_LOAD_X509
void __init evm_load_x509(void)
{
int rc;
rc = integrity_load_x509(INTEGRITY_KEYRING_EVM, CONFIG_EVM_X509_PATH);
if (!rc)
evm_initialized |= EVM_INIT_X509;
}
#endif
static int __init init_evm(void)
{
int error;
struct list_head *pos, *q;
evm_init_config();
error = integrity_init_keyring(INTEGRITY_KEYRING_EVM);
if (error)
goto error;
error = evm_init_secfs();
if (error < 0) {
pr_info("Error registering secfs\n");
goto error;
}
error:
if (error != 0) {
if (!list_empty(&evm_config_xattrnames)) {
list_for_each_safe(pos, q, &evm_config_xattrnames)
list_del(pos);
}
}
return error;
}
late_initcall(init_evm);
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