This is a note to let you know that I've just added the patch titled
evm: prohibit userspace writing 'security.evm' HMAC value
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
evm-prohibit-userspace-writing-security.evm-hmac-value.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2fb1c9a4f2dbc2f0bd2431c7fa64d0b5483864e4 Mon Sep 17 00:00:00 2001
From: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
Date: Sun, 11 May 2014 00:05:23 -0400
Subject: evm: prohibit userspace writing 'security.evm' HMAC value
From: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
security/integrity/evm/evm_main.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -271,12 +271,20 @@ static int evm_protect_xattr(struct dent
* @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);
}
Patches currently in stable-queue which might be from zohar@xxxxxxxxxxxxxxxxxx are
queue-3.4/evm-prohibit-userspace-writing-security.evm-hmac-value.patch
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