On 10/20/2022 6:55 AM, Nicolas Bouchinet wrote:
> From: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx>
> ---
> 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
#define MAX_LSM_EVM_XATTR \
2 + /* IMA and EVM */ \
(IS_ENABLED(CONFIG_SECURITY_SELINUX) ? 1 : 0) + \
(IS_ENABLED(CONFIG_SECURITY_SMACK) ? 1 : 0) + \
(IS_ENABLED(CONFIG_SECURITY_APPARMOR) ? 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)
> @@ -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; \
> +})
> +
No. Please open code this in the one place it is used.
> /* 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);
