diff mbox series

[v3,04/10] evm: Use the metadata inode to calculate metadata hash

Message ID 20240223172513.4049959-5-stefanb@linux.ibm.com (mailing list archive)
State Handled Elsewhere
Delegated to: Paul Moore
Headers show
Series evm: Support signatures on stacked filesystem | expand

Commit Message

Stefan Berger Feb. 23, 2024, 5:25 p.m. UTC
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 file's metadata inode and use it to calculate the metadata
hash with.

Co-developed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Acked-by: Amir Goldstein <amir73il@gmail.com>
---
 security/integrity/evm/evm_crypto.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Mimi Zohar March 19, 2024, 10:51 p.m. UTC | #1
On Fri, 2024-02-23 at 12:25 -0500, Stefan Berger wrote:
> 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 file's metadata inode and use it to calculate the metadata
> hash with.
> 
> Co-developed-by: Mimi Zohar <zohar@linux.ibm.com>
> Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
> Acked-by: Amir Goldstein <amir73il@gmail.com>

Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
diff mbox series

Patch

diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index 7552d49d0725..35416f55391c 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;