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Commit 74de6684 authored by Dmitry Kasatkin's avatar Dmitry Kasatkin Committed by Mimi Zohar
Browse files

evm: add file system uuid to EVM hmac 



EVM uses the same key for all file systems to calculate the HMAC,
making it possible to paste inodes from one file system on to another
one, without EVM being able to detect it.  To prevent such an attack,
it is necessary to make the EVM HMAC file system specific.

This patch uses the file system UUID, a file system unique identifier,
to bind the EVM HMAC to the file system. The value inode->i_sb->s_uuid
is used for the HMAC hash calculation, instead of using it for deriving
the file system specific key.  Initializing the key for every inode HMAC
calculation is a bit more expensive operation than adding the uuid to
the HMAC hash.

Changing the HMAC calculation method or adding additional info to the
calculation, requires existing EVM labeled file systems to be relabeled.
This patch adds a Kconfig HMAC version option for backwards compatability.

Changelog v1:
- squash "hmac version setting"
Changelog v0:
- add missing Kconfig depends (Mimi)

Signed-off-by: default avatarDmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: default avatarMimi Zohar <zohar@linux.vnet.ibm.com>
parent 6e38bfaa

security/integrity/evm/Kconfig

+13 −0
Original line number Diff line number Diff line
@@ -11,3 +11,16 @@ config EVM 
	  integrity attacks.



	  If you are unsure how to answer this question, answer N.



config EVM_HMAC_VERSION

	int "EVM HMAC version"

	depends on EVM

	default 2

	help

	  This options adds EVM HMAC version support.

	  1 - original version

	  2 - add per filesystem unique identifier (UUID) (default)



	  WARNING: changing the HMAC calculation method or adding 

	  additional info to the calculation, requires existing EVM

	  labeled file systems to be relabeled.

security/integrity/evm/evm.h

+1 −0
Original line number Diff line number Diff line
@@ -24,6 +24,7 @@ 
extern int evm_initialized;

extern char *evm_hmac;

extern char *evm_hash;

extern int evm_hmac_version;



extern struct crypto_shash *hmac_tfm;

extern struct crypto_shash *hash_tfm;

security/integrity/evm/evm_crypto.c

+3 −0
Original line number Diff line number Diff line
@@ -110,6 +110,9 @@ static void hmac_add_misc(struct shash_desc *desc, struct inode *inode, 
	hmac_misc.gid = from_kgid(&init_user_ns, inode->i_gid);

	hmac_misc.mode = inode->i_mode;

	crypto_shash_update(desc, (const u8 *)&hmac_misc, sizeof hmac_misc);

	if (evm_hmac_version > 1)

		crypto_shash_update(desc, inode->i_sb->s_uuid,

				    sizeof(inode->i_sb->s_uuid));

	crypto_shash_final(desc, digest);

}

security/integrity/evm/evm_main.c

+1 −0
Original line number Diff line number Diff line
@@ -26,6 +26,7 @@ int evm_initialized; 


char *evm_hmac = "hmac(sha1)";

char *evm_hash = "sha1";

int evm_hmac_version = CONFIG_EVM_HMAC_VERSION;



char *evm_config_xattrnames[] = {

#ifdef CONFIG_SECURITY_SELINUX