Re: [PATCH v2 14/25] evm: add support for fscaps security hooks

Roberto Sassu
2024-03-04T15:01:52Z

On Wed, 2024-02-21 at 15:24 -0600, Seth Forshee (DigitalOcean) wrote:
> Support the new fscaps security hooks by converting the vfs_caps to raw
> xattr data and then handling them the same as other xattrs.

I realized that you need to register hooks for IMA too.

This should be the content to add in ima_appraise.c:

int ima_inode_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
const struct vfs_caps *caps, int flags)
{
if (evm_revalidate_status(XATTR_NAME_CAPS))
ima_reset_appraise_flags(d_backing_inode(dentry), false);

return 0;
}

int ima_inode_remove_fscaps(struct mnt_idmap *idmap, struct dentry *dentry)
{
return ima_inode_set_fscaps(idmap, dentry, NULL, XATTR_REPLACE);
}

Thanks

Roberto

> Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
> ---
> include/linux/evm.h | 39 +++++++++++++++++++++++++
> security/integrity/evm/evm_main.c | 60 +++++++++++++++++++++++++++++++++++++++
> 2 files changed, 99 insertions(+)
>
> diff --git a/include/linux/evm.h b/include/linux/evm.h
> index 36ec884320d9..aeb9ff52ad22 100644
> --- a/include/linux/evm.h
> +++ b/include/linux/evm.h
> @@ -57,6 +57,20 @@ static inline void evm_inode_post_set_acl(struct dentry *dentry,
> {
> return evm_inode_post_setxattr(dentry, acl_name, NULL, 0);
> }
> +extern int evm_inode_set_fscaps(struct mnt_idmap *idmap,
> + struct dentry *dentry,
> + const struct vfs_caps *caps, int flags);
> +static inline int evm_inode_remove_fscaps(struct dentry *dentry)
> +{
> + return evm_inode_set_fscaps(&nop_mnt_idmap, dentry, NULL, XATTR_REPLACE);
> +}
> +extern void evm_inode_post_set_fscaps(struct mnt_idmap *idmap,
> + struct dentry *dentry,
> + const struct vfs_caps *caps, int flags);
> +static inline void evm_inode_post_remove_fscaps(struct dentry *dentry)
> +{
> + return evm_inode_post_set_fscaps(&nop_mnt_idmap, dentry, NULL, 0);
> +}
>
> int evm_inode_init_security(struct inode *inode, struct inode *dir,
> const struct qstr *qstr, struct xattr *xattrs,
> @@ -164,6 +178,31 @@ static inline void evm_inode_post_set_acl(struct dentry *dentry,
> return;
> }
>
> +static inline int evm_inode_set_fscaps(struct mnt_idmap *idmap,
> + struct dentry *dentry,
> + const struct vfs_caps *caps, int flags)
> +{
> + return 0;
> +}
> +
> +static inline int evm_inode_remove_fscaps(struct dentry *dentry)
> +{
> + return 0;
> +}
> +
> +static inline void evm_inode_post_set_fscaps(struct mnt_idmap *idmap,
> + struct dentry *dentry,
> + const struct vfs_caps *caps,
> + int flags)
> +{
> + return;
> +}
> +
> +static inline void evm_inode_post_remove_fscaps(struct dentry *dentry)
> +{
> + return;
> +}
> +
> static inline int evm_inode_init_security(struct inode *inode, struct inode *dir,
> const struct qstr *qstr,
> struct xattr *xattrs,
> diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
> index cc7956d7878b..ecf4634a921a 100644
> --- a/security/integrity/evm/evm_main.c
> +++ b/security/integrity/evm/evm_main.c
> @@ -805,6 +805,66 @@ void evm_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
> evm_update_evmxattr(dentry, xattr_name, NULL, 0);
> }
>
> +int evm_inode_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> + const struct vfs_caps *caps, int flags)
> +{
> + struct inode *inode = d_inode(dentry);
> + struct vfs_ns_cap_data nscaps;
> + const void *xattr_data = NULL;
> + int size = 0;
> +
> + /* Policy permits modification of the protected xattrs even though
> + * there's no HMAC key loaded
> + */
> + if (evm_initialized & EVM_ALLOW_METADATA_WRITES)
> + return 0;
> +
> + if (caps) {
> + size = vfs_caps_to_xattr(idmap, i_user_ns(inode), caps, &nscaps,
> + sizeof(nscaps));
> + if (size < 0)
> + return size;
> + xattr_data = &nscaps;
> + }
> +
> + return evm_protect_xattr(idmap, dentry, XATTR_NAME_CAPS, xattr_data, size);
> +}
> +
> +void evm_inode_post_set_fscaps(struct mnt_idmap *idmap, struct dentry *dentry,
> + const struct vfs_caps *caps, int flags)
> +{
> + struct inode *inode = d_inode(dentry);
> + struct vfs_ns_cap_data nscaps;
> + const void *xattr_data = NULL;
> + int size = 0;
> +
> + if (!evm_revalidate_status(XATTR_NAME_CAPS))
> + return;
> +
> + evm_reset_status(dentry->d_inode);
> +
> + if (!(evm_initialized & EVM_INIT_HMAC))
> + return;
> +
> + if (is_unsupported_fs(dentry))
> + return;
> +
> + if (caps) {
> + size = vfs_caps_to_xattr(idmap, i_user_ns(inode), caps, &nscaps,
> + sizeof(nscaps));
> + /*
> + * The fscaps here should have been converted to an xattr by
> + * evm_inode_set_fscaps() already, so a failure to convert
> + * here is a bug.
> + */
> + if (WARN_ON_ONCE(size < 0))
> + return;
> + xattr_data = &nscaps;
> + }
> +
> + evm_update_evmxattr(dentry, XATTR_NAME_CAPS, xattr_data, size);
> +}
> +
> static int evm_attr_change(struct mnt_idmap *idmap,
> struct dentry *dentry, struct iattr *attr)
> {
>