[PATCH v2 5/9] evm: Use the inode holding the metadata to calculate metadata hash

[Stefan Berger]

Changes to file attributes (mode bits, uid, gid) on the lower layer are
not taken into account when d_backing_inode() is used when a file is
accessed on the overlay layer and this file has not yet been copied up.
This is because d_backing_inode() does not return the real inode of the
lower layer but instead returns the backing inode which in this case
holds wrong file attributes. Further, when CONFIG_OVERLAY_FS_METACOPY is
enabled and a copy-up is triggered due to file metadata changes, then
the metadata are held by the backing inode while the data are still held
by the real inode. Therefore, use d_inode(d_real(dentry, D_REAL_METADATA))
to get to the inode holding the file's metadata and use it to calculate
the metadata hash with.

Signed-off-by: Stefan Berger <stefanb at linux.ibm.com>
---
 security/integrity/evm/evm_crypto.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index b1ffd4cc0b44..51e24a75742c 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -223,7 +223,7 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
 				 size_t req_xattr_value_len,
 				 uint8_t type, struct evm_digest *data)
 {
-	struct inode *inode = d_backing_inode(dentry);
+	struct inode *inode = d_inode(d_real(dentry, D_REAL_METADATA));
 	struct xattr_list *xattr;
 	struct shash_desc *desc;
 	size_t xattr_size = 0;
-- 
2.43.0