[PATCH v5] evm: Correct inode_init_security hooks behaviors
Nicolas Bouchinet
nicolas.bouchinet at clip-os.org
Fri Nov 25 15:57:15 UTC 2022
From: Nicolas Bouchinet <nicolas.bouchinet at ssi.gouv.fr>
Fixes a NULL pointer dereference occurring 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.
The `call_int_hook_xattr` macro has been inlined into the
`security_inode_init_security` hook in order to check hooks return
values and skip ones who doesn't init `xattrs`.
Modify `evm_init_hmac` function to init the EVM hmac using every
entry of the given xattr array.
The `MAX_LSM_EVM_XATTR` value is now based on the security modules
compiled in, 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: roberto.sassu at huaweicloud.com
Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet at ssi.gouv.fr>
---
Changes since v4:
https://lore.kernel.org/linux-integrity/Y1lElHVQGT%2F1Pa6O@archlinux/
* Updated the `security_inode_init_security()` hook documentation.
* Moved the NULL pointer dereference check from `evm_protected_xattr_common()`
inside the LSM hook calls loop of the `security_inode_init_security()`
function (as suggested by Roberto Sassu).
* Fixes the error return conditions of the `hlist_for_each_entry()`
loop in the `security_inode_init_security()` function (as suggested by Roberto Sassu).
* Fixes the `evm_xattr` pointer calculation before the `evm_inode_init_security()`
call (as suggested by Roberto Sassu).
Changes since v3:
https://lore.kernel.org/linux-integrity/Y1fu4jofqLHVDprT@archlinux/
* Fixes compilation error reported by the kernel test robot.
Changes since v2:
https://lore.kernel.org/linux-integrity/Y1K3bf+dtNnVe7DG@archlinux/
* The `evm_init_hmacs` has been merged with `evm_init_hmac`
(as suggested by Mimi Zohar).
* The commit message has been updated to match the patch changes.
Changes since v1:
https://lore.kernel.org/linux-integrity/Y1FTSIo+1x+4X0LS@archlinux/
* The `call_int_hook_xattr` macro has been inlined into the
`security_inode_init_security` hook (as suggested by Paul Moor,
Mickaël Salaün and Casey Schaufler).
* The MAX_LSM_EVM_XATTR value is processed based on compiled LSMs (as
proposed by Casey Schaufler).
* Various typos and cosmetic changes has been fixed (as suggested by
Mickaël Salaün)
* A MAX_LSM_EVM_XATTR test has been wrapped in a WARN_ON_ONCE macro (as
suggested by Mickaël Salaün).
---
include/linux/lsm_hook_defs.h | 2 +-
include/linux/lsm_hooks.h | 6 ++---
security/integrity/evm/evm.h | 1 +
security/integrity/evm/evm_crypto.c | 9 +++++--
security/integrity/evm/evm_main.c | 5 ++--
security/security.c | 39 ++++++++++++++++++++++-------
6 files changed, 44 insertions(+), 18 deletions(-)
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index ec119da1d89b4..0ba396f08c4f1 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 4ec80b96c22e7..8a2762f7e75f5 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -229,15 +229,15 @@
* 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.
* @inode contains the inode structure of the newly created inode.
* @dir contains the inode structure of the parent directory.
* @qstr contains the last path component of the new object
- * @name will be set to the allocated name suffix (e.g. selinux).
+ * @name will be set to a name suffix (e.g. selinux).
* @value will be set to the allocated attribute value.
* @len will be set to the length of the value.
* Returns 0 if @name and @value have been successfully set,
diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
index f8b8c5004fc7c..6d9628ca7c246 100644
--- a/security/integrity/evm/evm.h
+++ b/security/integrity/evm/evm.h
@@ -61,5 +61,6 @@ int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
int evm_init_hmac(struct inode *inode, const struct xattr *xattr,
char *hmac_val);
int evm_init_secfs(void);
+int evm_protected_xattr(const char *req_xattr_name);
#endif
diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 708de9656bbd2..06639f3cfb383 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -385,7 +385,7 @@ int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
return rc;
}
-int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
+int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattrs,
char *hmac_val)
{
struct shash_desc *desc;
@@ -396,7 +396,12 @@ int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattr,
return PTR_ERR(desc);
}
- crypto_shash_update(desc, lsm_xattr->value, lsm_xattr->value_len);
+ 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;
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 23d484e05e6f2..35a060a6124c5 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -305,7 +305,7 @@ 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);
}
@@ -852,8 +852,7 @@ int evm_inode_init_security(struct inode *inode,
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);
diff --git a/security/security.c b/security/security.c
index 79d82cb6e4696..6cdd3fdc08fbc 100644
--- a/security/security.c
+++ b/security/security.c
@@ -30,7 +30,11 @@
#include <linux/msg.h>
#include <net/flow.h>
-#define MAX_LSM_EVM_XATTR 2
+#define MAX_LSM_EVM_XATTR \
+ ((IS_ENABLED(CONFIG_EVM) ? 1 : 0) + \
+ (IS_ENABLED(CONFIG_SECURITY_SELINUX) ? 1 : 0) + \
+ (IS_ENABLED(CONFIG_SECURITY_SMACK) ? 1 : 0) + \
+ (IS_ENABLED(CONFIG_BPF_LSM) ? 1 : 0))
/* How many LSMs were built into the kernel? */
#define LSM_COUNT (__end_lsm_info - __start_lsm_info)
@@ -1093,9 +1097,11 @@ int security_inode_init_security(struct inode *inode, struct inode *dir,
const struct qstr *qstr,
const initxattrs initxattrs, void *fs_data)
{
+ int initialized_lsms = 0;
+ int ret = -EOPNOTSUPP;
struct xattr new_xattrs[MAX_LSM_EVM_XATTR + 1];
struct xattr *lsm_xattr, *evm_xattr, *xattr;
- int ret;
+ struct security_hook_list *hook_ptr;
if (unlikely(IS_PRIVATE(inode)))
return 0;
@@ -1105,15 +1111,30 @@ 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,
- &lsm_xattr->name,
- &lsm_xattr->value,
- &lsm_xattr->value_len);
- if (ret)
+ hlist_for_each_entry(hook_ptr, &security_hook_heads.inode_init_security,
+ list) {
+ ret = hook_ptr->hook.inode_init_security(inode, dir, qstr,
+ &lsm_xattr->name,
+ &lsm_xattr->value,
+ &lsm_xattr->value_len);
+ if (ret == -EOPNOTSUPP)
+ continue;
+ if (ret != 0)
+ goto out;
+ if (WARN_ON_ONCE(initialized_lsms >= MAX_LSM_EVM_XATTR ||
+ !lsm_xattr->name ||
+ !lsm_xattr->value)) {
+ ret = -ENOMEM;
+ goto out;
+ }
+ lsm_xattr++;
+ initialized_lsms++;
+ }
+ if (!initialized_lsms)
goto out;
- evm_xattr = lsm_xattr + 1;
- ret = evm_inode_init_security(inode, lsm_xattr, evm_xattr);
+ evm_xattr = lsm_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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