Re: [PATCH v6 2/5] IMA: block writes of the security.ima xattr with unsupported algorithms

[Mimi Zohar <zohar@xxxxxxxxxxxxx>]

On Wed, 2021-08-04 at 09:20 +0000, THOBY Simon wrote:
> +static int validate_hash_algo(struct dentry *dentry,
> +                                  const struct evm_ima_xattr_data *xattr_value,
> +                                  size_t xattr_value_len)
> +{
> +       int result = 0;
> +       char *path = NULL, *pathbuf = NULL;
> +       enum hash_algo xattr_hash_algo;
> +
> +       xattr_hash_algo = ima_get_hash_algo(xattr_value, xattr_value_len);
> +
> +       if (likely(xattr_hash_algo == ima_hash_algo ||
> +                  crypto_has_alg(hash_algo_name[xattr_hash_algo], 0, 0)))
> +               return result;
> +
> +       result = -EACCES;
> +
> +       pathbuf = kmalloc(PATH_MAX, GFP_KERNEL);
> +       if (!pathbuf)
> +               return result;
> +
> +       path = dentry_path(dentry, pathbuf, PATH_MAX);
> +
> +       integrity_audit_msg(AUDIT_INTEGRITY_DATA, d_inode(dentry), path,
> +                           "collect_data", "unavailable-hash-algorithm",
> +                           result, 0);

"collect_data" refers to calculating the file hash,
ima_collect_measurement(), which may be stored in the measurement list,
used for verifying the signature and/or included in the audit record.

validate_hash_algo() verifies the hash algorithm before allowing the
file hash or signature to be written as security.ima.  Instead of
"collect_data" it should be "set_data" or something similar.

thanks,

Mimi

> +
> +       kfree(pathbuf);
> +
> +       return result;