From: Mimi Zohar <zohar@linux.ibm.com>
To: Roberto Sassu <roberto.sassu@huawei.com>, mjg59@google.com
Cc: linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org, silviu.vlasceanu@huawei.com
Subject: Re: [PATCH v2 09/12] evm: Allow setxattr() and setattr() if metadata digest won't change
Date: Thu, 17 Sep 2020 09:15:42 -0400 [thread overview]
Message-ID: <65512863d3cee25b0ba40fce8e819772b20c363c.camel@linux.ibm.com> (raw)
In-Reply-To: <20200904092643.20013-5-roberto.sassu@huawei.com>
Hi Roberto,
"if" doesn't belong in the subject line. In this case, instead of "if
metadata ...", how about something like "for unmodified metadata"?
On Fri, 2020-09-04 at 11:26 +0200, Roberto Sassu wrote:
> With the patch to allow xattr/attr operations if a portable signature
> verification fails, cp and tar can copy all xattrs/attrs so that at the
> end of the process verification succeeds.
>
> However, it might happen that xattrs/attrs are already set to the correct
^ the xattrs/attrs
> value (taken at signing time) and signature verification succeeds before
> the copy is completed. For example, an archive might contains files owned
^ has completed.
> by root and the archive is extracted by root.
>
> Then, since portable signatures are immutable, all subsequent operations
> fail (e.g. fchown()), even if the operation is legitimate (does not alter
> the current value).
>
> This patch avoids this problem by reporting successful operation to user
> space when that operation does not alter the current value of xattrs/attrs.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
<snip>
> +/*
> + * evm_xattr_change - check if passed xattr value differs from current value
> + * @dentry: pointer to the affected dentry
> + * @xattr_name: requested xattr
> + * @xattr_value: requested xattr value
> + * @xattr_value_len: requested xattr value length
> + *
> + * Check if passed xattr value differs from current value.
> + *
> + * Returns 1 if passed xattr value differs from current value, 0 otherwise.
> + */
> +static int evm_xattr_change(struct dentry *dentry, const char *xattr_name,
> + const void *xattr_value, size_t xattr_value_len)
> +{
> + char *xattr_data = NULL;
> + int rc = 0;
> +
> + if (posix_xattr_acl(xattr_name))
> + return evm_xattr_acl_change(dentry, xattr_name, xattr_value,
> + xattr_value_len);
> +
> + rc = vfs_getxattr_alloc(dentry, xattr_name, &xattr_data, 0, GFP_NOFS);
> + if (rc < 0)
> + return 1;
> +
> + if (rc == xattr_value_len)
> + rc = memcmp(xattr_value, xattr_data, rc);
This should probably be changed to crypto_memneq(). Refer to commit
613317bd212c ("EVM: Use crypto_memneq() for digest comparisons").
thanks,
Mimi
> + else
> + rc = 1;
> +
> + kfree(xattr_data);
> + return rc;
> +}
> +
>
next prev parent reply other threads:[~2020-09-17 13:20 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-04 9:23 [PATCH v2 00/12] IMA/EVM fixes Roberto Sassu
2020-09-04 9:23 ` [PATCH v2 01/12] ima: Don't ignore errors from crypto_shash_update() Roberto Sassu
2020-09-04 9:23 ` [PATCH v2 02/12] ima: Remove semicolon at the end of ima_get_binary_runtime_size() Roberto Sassu
2020-09-04 9:23 ` [PATCH v2 03/12] evm: Check size of security.evm before using it Roberto Sassu
2020-09-04 9:23 ` [PATCH v2 04/12] evm: Execute evm_inode_init_security() only when the HMAC key is loaded Roberto Sassu
2020-09-16 16:15 ` Mimi Zohar
2020-09-04 9:26 ` [PATCH v2 05/12] evm: Load EVM key in ima_load_x509() to avoid appraisal Roberto Sassu
2020-09-04 9:26 ` [PATCH v2 06/12] evm: Refuse EVM_ALLOW_METADATA_WRITES only if the HMAC key is loaded Roberto Sassu
2020-09-04 9:26 ` [PATCH v2 07/12] evm: Introduce EVM_RESET_STATUS atomic flag Roberto Sassu
2020-09-17 12:01 ` Mimi Zohar
2020-09-17 17:36 ` Roberto Sassu
2020-09-17 17:47 ` Mimi Zohar
2020-09-04 9:26 ` [PATCH v2 08/12] evm: Allow xattr/attr operations for portable signatures if check fails Roberto Sassu
2020-09-17 12:32 ` Mimi Zohar
2020-09-04 9:26 ` [PATCH v2 09/12] evm: Allow setxattr() and setattr() if metadata digest won't change Roberto Sassu
2020-09-17 13:15 ` Mimi Zohar [this message]
2020-09-04 9:26 ` [PATCH v2 10/12] ima: Allow imasig requirement to be satisfied by EVM portable signatures Roberto Sassu
2020-09-04 9:26 ` [PATCH v2 11/12] ima: Introduce template field evmsig and write to field sig as fallback Roberto Sassu
2020-09-17 14:25 ` Mimi Zohar
2020-09-17 15:05 ` Roberto Sassu
2020-09-17 15:55 ` Mimi Zohar
2020-09-04 9:26 ` [PATCH v2 12/12] ima: Don't remove security.ima if file must not be appraised Roberto Sassu
2020-09-16 16:14 ` [PATCH v2 00/12] IMA/EVM fixes Mimi Zohar
2020-09-17 14:33 ` Mimi Zohar
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