[PATCH] evm: Use ordered xattrs list to calculate HMAC in evm_init_hmac()

[PATCH] evm: Use ordered xattrs list to calculate HMAC in evm_init_hmac()

[Roberto Sassu]

From: Roberto Sassu <roberto.sassu@huawei.com>

Commit 8e5d9f916a96 ("smack: deduplicate xattr setting in
smack_inode_init_security()") introduced xattr_dupval() to simplify setting
the xattrs to be provided by the SMACK LSM on inode creation, in the
smack_inode_init_security().

Unfortunately, moving lsm_get_xattr_slot() caused the SMACK64TRANSMUTE
xattr be added in the array of new xattrs before SMACK64. This causes the
HMAC of xattrs calculated by evm_init_hmac() for new files to diverge from
the one calculated by both evm_calc_hmac_or_hash() and evmctl.

evm_init_hmac() calculates the HMAC of the xattrs of new files based on the
order LSMs provide them, while evm_calc_hmac_or_hash() and evmctl calculate
the HMAC based on an ordered xattrs list.

Fix the issue by making evm_init_hmac() calculate the HMAC of new files
based on the ordered xattrs list too.

Fixes: 8e5d9f916a96 ("smack: deduplicate xattr setting in smack_inode_init_security()")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 security/integrity/evm/evm_crypto.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index a5e730ffda57..5a8cef45bacf 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -401,6 +401,7 @@ int evm_init_hmac(struct inode *inode, const struct xattr *xattrs,
 {
 	struct shash_desc *desc;
 	const struct xattr *xattr;
+	struct xattr_list *xattr_entry;
 
 	desc = init_desc(EVM_XATTR_HMAC, HASH_ALGO_SHA1);
 	if (IS_ERR(desc)) {
@@ -408,11 +409,16 @@ int evm_init_hmac(struct inode *inode, const struct xattr *xattrs,
 		return PTR_ERR(desc);
 	}
 
-	for (xattr = xattrs; xattr->name; xattr++) {
-		if (!evm_protected_xattr(xattr->name))
-			continue;
+	list_for_each_entry_lockless(xattr_entry, &evm_config_xattrnames,
+				     list) {
+		for (xattr = xattrs; xattr->name; xattr++) {
+			if (strcmp(xattr_entry->name +
+				   XATTR_SECURITY_PREFIX_LEN, xattr->name) != 0)
+				continue;
 
-		crypto_shash_update(desc, xattr->value, xattr->value_len);
+			crypto_shash_update(desc, xattr->value,
+					    xattr->value_len);
+		}
 	}
 
 	hmac_add_misc(desc, inode, EVM_XATTR_HMAC, hmac_val);
-- 
2.43.0

Re: [PATCH] evm: Use ordered xattrs list to calculate HMAC in evm_init_hmac()

[Mimi Zohar]

On Thu, 2026-01-22 at 09:07 +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@huawei.com>
> 
> Commit 8e5d9f916a96 ("smack: deduplicate xattr setting in
> smack_inode_init_security()") introduced xattr_dupval() to simplify setting
> the xattrs to be provided by the SMACK LSM on inode creation, in the
> smack_inode_init_security().
> 
> Unfortunately, moving lsm_get_xattr_slot() caused the SMACK64TRANSMUTE
> xattr be added in the array of new xattrs before SMACK64. This causes the
> HMAC of xattrs calculated by evm_init_hmac() for new files to diverge from
> the one calculated by both evm_calc_hmac_or_hash() and evmctl.
> 
> evm_init_hmac() calculates the HMAC of the xattrs of new files based on the
> order LSMs provide them, while evm_calc_hmac_or_hash() and evmctl calculate
> the HMAC based on an ordered xattrs list.
> 
> Fix the issue by making evm_init_hmac() calculate the HMAC of new files
> based on the ordered xattrs list too.
> 
> Fixes: 8e5d9f916a96 ("smack: deduplicate xattr setting in smack_inode_init_security()")
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>

Thanks, Roberto.  The patch is now queued in next-integrity.