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References: <20240205182506.3569743-1-stefanb@linux.ibm.com> <20240205182506.3569743-6-stefanb@linux.ibm.com>
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From: Amir Goldstein <amir73il@gmail.com>
Date: Tue, 6 Feb 2024 17:33:38 +0200
Message-ID: <CAOQ4uxhhRo20oCrDvs42e4m=HzdUSZ+YtMv8JVykuNoHGP8ypA@mail.gmail.com>
Subject: Re: [PATCH v2 5/9] evm: Use the inode holding the metadata to
 calculate metadata hash
To: Stefan Berger <stefanb@linux.ibm.com>
Cc: linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, 
	linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org, 
	paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, zohar@linux.ibm.com, 
	roberto.sassu@huawei.com, brauner@kernel.org, miklos@szeredi.hu
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On Mon, Feb 5, 2024 at 8:25=E2=80=AFPM Stefan Berger <stefanb@linux.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@linux.ibm.com>

Acked-by: Amir Goldstein <amir73il@gmail.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 *dentr=
y,
>                                  size_t req_xattr_value_len,
>                                  uint8_t type, struct evm_digest *data)
>  {
> -       struct inode *inode =3D d_backing_inode(dentry);
> +       struct inode *inode =3D d_inode(d_real(dentry, D_REAL_METADATA));
>         struct xattr_list *xattr;
>         struct shash_desc *desc;
>         size_t xattr_size =3D 0;
> --
> 2.43.0
>