diff options
authorMimi Zohar <zohar@linux.vnet.ibm.com>2014-05-11 00:05:23 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-06-26 15:10:28 -0400
commit12a38b8f1dd7c65d01aa4c759f29a700c194ecec (patch)
parent7f53daea4dd53f43dd10ac24f752f74063abe4fa (diff)
evm: prohibit userspace writing 'security.evm' HMAC value
commit 2fb1c9a4f2dbc2f0bd2431c7fa64d0b5483864e4 upstream. Calculating the 'security.evm' HMAC value requires access to the EVM encrypted key. Only the kernel should have access to it. This patch prevents userspace tools(eg. setfattr, cp --preserve=xattr) from setting/modifying the 'security.evm' HMAC value directly. Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 10 insertions, 2 deletions
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 8901501425f4..c487715698ab 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -271,12 +271,20 @@ 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,