From: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx> 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@xxxxxxxxxxxxxxx Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Nicolas Bouchinet <nicolas.bouchinet@xxxxxxxxxxx> --- 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. --- include/linux/lsm_hook_defs.h | 2 +- include/linux/lsm_hooks.h | 4 ++-- security/integrity/evm/evm_crypto.c | 11 ++++++++-- security/integrity/evm/evm_main.c | 7 ++++--- security/security.c | 31 ++++++++++++++++++++++------- 5 files changed, 40 insertions(+), 15 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_crypto.c b/security/integrity/evm/evm_crypto.c index 708de9656bbd..c82f271cfd19 100644 --- a/security/integrity/evm/evm_crypto.c +++ b/security/integrity/evm/evm_crypto.c @@ -385,7 +385,9 @@ 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_protected_xattr(const char *req_xattr_name); + +int evm_init_hmac(struct inode *inode, const struct xattr *lsm_xattrs, char *hmac_val) { struct shash_desc *desc; @@ -396,7 +398,12 @@ 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 2e6fb6e2ffd2..0420453a80e8 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); } @@ -841,8 +843,7 @@ 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 14d30fec8a00..79524f8734f1 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) @@ -1091,9 +1095,11 @@ int security_inode_init_security(struct inode *inode, struct inode *dir, const struct qstr *qstr, const initxattrs initxattrs, void *fs_data) { + int i = 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; @@ -1103,15 +1109,26 @@ 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); + 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 (WARN_ON_ONCE(i >= MAX_LSM_EVM_XATTR)) + ret = -ENOMEM; + if (ret != 0) + break; + lsm_xattr++; + i++; + } if (ret) 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
