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

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Date: Tue, 6 Feb 2024 17:33:38 +0200
From: Amir Goldstein <amir73il@...il.com>
To: Stefan Berger <stefanb@...ux.ibm.com>
Cc: linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org, 
	linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org, 
	paul@...l-moore.com, jmorris@...ei.org, serge@...lyn.com, zohar@...ux.ibm.com, 
	roberto.sassu@...wei.com, brauner@...nel.org, miklos@...redi.hu
Subject: Re: [PATCH v2 5/9] evm: Use the inode holding the metadata to
 calculate metadata hash

On Mon, Feb 5, 2024 at 8:25 PM Stefan Berger <stefanb@...ux.ibm.com> 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 inode holding the file's metadata and use it to calculate
> the metadata hash with.
>
> Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>

Acked-by: Amir Goldstein <amir73il@...il.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
>