[PATCH] evm: Correct inode_init_security hooks behaviors
Nicolas Bouchinet
nicolas.bouchinet at clip-os.org
Thu Oct 20 13:55:20 UTC 2022
From: Nicolas Bouchinet <nicolas.bouchinet at ssi.gouv.fr>
Fixes a NULL pointer dereference occuring in the
`evm_protected_xattr_common` function of the EVM LSM. The bug is
triggered if a `inode_init_security` hook returns 0 without initializing
the given `struct xattr` fields (which is the case of BPF) and if no
other LSM overrides thoses fields after. This also leads to memory
leaks.
Adds a `call_int_hook_xattr` macro that fetches and feed the
`new_xattrs` array with every called hook xattr values.
Adds a `evm_init_hmacs` function which init the EVM hmac using every
entry of the array contrary to `evm_init_hmac`.
Fixes the `evm_inode_init_security` function to use `evm_init_hmacs`.
The `MAX_LSM_EVM_XATTR` value has been raised to 5 which gives room for
SMACK, SELinux, Apparmor, BPF and IMA/EVM security attributes.
Changes the default return value of the `inode_init_security` hook
definition to `-EOPNOTSUPP`.
Changes the hook documentation to match the behavior of the LSMs using
it (only xattr->value is initialised with kmalloc and thus is the only
one that should be kfreed by the caller).
Cc: stable at vger.kernel.org
Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet at ssi.gouv.fr>
---
include/linux/lsm_hook_defs.h | 2 +-
include/linux/lsm_hooks.h | 4 ++--
security/integrity/evm/evm.h | 2 ++
security/integrity/evm/evm_crypto.c | 23 ++++++++++++++++++++++-
security/integrity/evm/evm_main.c | 11 ++++++-----
security/security.c | 29 ++++++++++++++++++++++++++---
6 files changed, 59 insertions(+), 12 deletions(-)
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 806448173033..e5dd0c0f6345 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -111,7 +111,7 @@ LSM_HOOK(int, 0, path_notify, const struct path *path, u64 mask,
unsigned int obj_type)
LSM_HOOK(int, 0, inode_alloc_security, struct inode *inode)
LSM_HOOK(void, LSM_RET_VOID, inode_free_security, struct inode *inode)
-LSM_HOOK(int, 0, inode_init_security, struct inode *inode,
+LSM_HOOK(int, -EOPNOTSUPP, inode_init_security, struct inode *inode,
struct inode *dir, const struct qstr *qstr, const char **name,
void **value, size_t *len)
LSM_HOOK(int, 0, inode_init_security_anon, struct inode *inode,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 84a0d7e02176..95aff9383de1 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -229,8 +229,8 @@
* This hook is called by the fs code as part of the inode creation
* transaction and provides for atomic labeling of the inode, unlike
* the post_create/mkdir/... hooks called by the VFS. The hook function
- * is expected to allocate the name and value via kmalloc, with the caller
- * being responsible for calling kfree after using them.
+ * is expected to allocate the value via kmalloc, with the caller
+ * being responsible for calling kfree after using it.
* If the security module does not use security attributes or does
* not wish to put a security attribute on this particular inode,
* then it should return -EOPNOTSUPP to skip this processing.
diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
index f8b8c5004fc7..a2f9886e924d 100644
--- a/security/integrity/evm/evm.h
+++ b/security/integrity/evm/evm.h
@@ -60,6 +60,8 @@ int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
struct evm_digest *data);
int evm_init_hmac(struct inode *inode, const struct xattr *xattr,
char *hmac_val);
+int evm_init_hmacs(struct inode *inode, const struct xattr *xattrs,
+ char *hmac_val);
int evm_init_secfs(void);
#endif
diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 708de9656bbd..e5a34306cab6 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -347,7 +347,6 @@ static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
return rc;
}
-
/*
* Calculate the hmac and update security.evm xattr
*
@@ -385,6 +384,28 @@ int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
return rc;
}
+int evm_protected_xattr(const char *req_xattr_name);
+
+int evm_init_hmacs(struct inode *inode, const struct xattr *lsm_xattrs,
+ char *hmac_val)
+{
+ struct shash_desc *desc;
+
+ desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
+ if (IS_ERR(desc)) {
+ pr_info("init_desc failed\n");
+ return PTR_ERR(desc);
+ }
+
+ for (int i = 0; lsm_xattrs[i].value != NULL; i++) {
+ if (evm_protected_xattr(lsm_xattrs[i].name))
+ crypto_shash_update(desc, lsm_xattrs[i].value, lsm_xattrs[i].value_len);
+ }
+ hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
+ kfree(desc);
+ return 0;
+}
+
int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
char *hmac_val)
{
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 2e6fb6e2ffd2..bb071c55d656 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -284,6 +284,8 @@ static int evm_protected_xattr_common(const char *req_xattr_name,
int found = 0;
struct xattr_list *xattr;
+ if (!req_xattr_name)
+ return found;
namelen = strlen(req_xattr_name);
list_for_each_entry_lockless(xattr, &evm_config_xattrnames, list) {
if (!all_xattrs && !xattr->enabled)
@@ -305,7 +307,7 @@ static int evm_protected_xattr_common(const char *req_xattr_name,
return found;
}
-static int evm_protected_xattr(const char *req_xattr_name)
+int evm_protected_xattr(const char *req_xattr_name)
{
return evm_protected_xattr_common(req_xattr_name, false);
}
@@ -835,14 +837,13 @@ void evm_inode_post_setattr(struct dentry *dentry, int ia_valid)
* evm_inode_init_security - initializes security.evm HMAC value
*/
int evm_inode_init_security(struct inode *inode,
- const struct xattr *lsm_xattr,
+ const struct xattr *lsm_xattrs,
struct xattr *evm_xattr)
{
struct evm_xattr *xattr_data;
int rc;
- if (!(evm_initialized & EVM_INIT_HMAC) ||
- !evm_protected_xattr(lsm_xattr->name))
+ if (!(evm_initialized & EVM_INIT_HMAC))
return 0;
xattr_data = kzalloc(sizeof(*xattr_data), GFP_NOFS);
@@ -850,7 +851,7 @@ int evm_inode_init_security(struct inode *inode,
return -ENOMEM;
xattr_data->data.type = EVM_XATTR_HMAC;
- rc = evm_init_hmac(inode, lsm_xattr, xattr_data->digest);
+ rc = evm_init_hmacs(inode, lsm_xattrs, xattr_data->digest);
if (rc < 0)
goto out;
diff --git a/security/security.c b/security/security.c
index 14d30fec8a00..47012c118536 100644
--- a/security/security.c
+++ b/security/security.c
@@ -30,7 +30,7 @@
#include <linux/msg.h>
#include <net/flow.h>
-#define MAX_LSM_EVM_XATTR 2
+#define MAX_LSM_EVM_XATTR 5
/* How many LSMs were built into the kernel? */
#define LSM_COUNT (__end_lsm_info - __start_lsm_info)
@@ -746,6 +746,29 @@ static int lsm_superblock_alloc(struct super_block *sb)
RC; \
})
+#define call_int_hook_xattr(XATTRS, FUNC, IRC, ...) ({ \
+ int RC = IRC; \
+ int i = 0; \
+ do { \
+ struct security_hook_list *P; \
+ \
+ hlist_for_each_entry(P, &security_hook_heads.FUNC, list) { \
+ RC = P->hook.FUNC(__VA_ARGS__); \
+ if (RC == -EOPNOTSUPP) \
+ continue; \
+ if (RC != 0 && RC != IRC) \
+ break; \
+ if (i >= MAX_LSM_EVM_XATTR) { \
+ RC = -ENOMEM; \
+ break; \
+ } \
+ XATTRS++; \
+ i++; \
+ } \
+ } while (0); \
+ RC; \
+})
+
/* Security operations */
int security_binder_set_context_mgr(const struct cred *mgr)
@@ -1103,7 +1126,7 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
dir, qstr, NULL, NULL, NULL);
memset(new_xattrs, 0, sizeof(new_xattrs));
lsm_xattr = new_xattrs;
- ret = call_int_hook(inode_init_security, -EOPNOTSUPP, inode, dir, qstr,
+ ret = call_int_hook_xattr(lsm_xattr, inode_init_security, -EOPNOTSUPP, inode, dir, qstr,
&lsm_xattr->name,
&lsm_xattr->value,
&lsm_xattr->value_len);
@@ -1111,7 +1134,7 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
goto out;
evm_xattr = lsm_xattr + 1;
- ret = evm_inode_init_security(inode, lsm_xattr, evm_xattr);
+ ret = evm_inode_init_security(inode, new_xattrs, evm_xattr);
if (ret)
goto out;
ret = initxattrs(inode, new_xattrs, fs_data);
--
2.38.1
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