diff options
| -rw-r--r-- | security/integrity/evm/evm_main.c | 12 |
1 files changed, 10 insertions, 2 deletions
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index cdbde176218..b9b2bebeb35 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c @@ -275,12 +275,20 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name, * @xattr_value: pointer to the new extended attribute value * @xattr_value_len: pointer to the new extended attribute value length * - * Updating 'security.evm' requires CAP_SYS_ADMIN privileges and that - * the current value is valid. + * 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 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; + + if ((strcmp(xattr_name, XATTR_NAME_EVM) == 0) + && (xattr_data->type == EVM_XATTR_HMAC)) + return -EPERM; return evm_protect_xattr(dentry, xattr_name, xattr_value, xattr_value_len); } |