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From: Casey Schaufler <casey@schaufler-ca.com>
To: Roberto Sassu <roberto.sassu@huawei.com>,
	zohar@linux.ibm.com, mjg59@google.com
Cc: linux-integrity@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Casey Schaufler <casey@schaufler-ca.com>
Subject: Re: [PATCH v5 04/12] ima: Move ima_reset_appraise_flags() call to post hooks
Date: Wed, 7 Apr 2021 09:17:48 -0700
Message-ID: <d4aba724-2935-467b-e57c-cd961112190b@schaufler-ca.com> (raw)
In-Reply-To: <20210407105252.30721-5-roberto.sassu@huawei.com>

On 4/7/2021 3:52 AM, Roberto Sassu wrote:
> ima_inode_setxattr() and ima_inode_removexattr() hooks are called before an
> operation is performed. Thus, ima_reset_appraise_flags() should not be
> called there, as flags might be unnecessarily reset if the operation is
> denied.
>
> This patch introduces the post hooks ima_inode_post_setxattr() and
> ima_inode_post_removexattr(), and adds the call to
> ima_reset_appraise_flags() in the new functions.
>
> Cc: Casey Schaufler <casey@schaufler-ca.com>
> Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
> ---
>  fs/xattr.c                            |  2 ++
>  include/linux/ima.h                   | 18 ++++++++++++++++++
>  security/integrity/ima/ima_appraise.c | 25 ++++++++++++++++++++++---
>  security/security.c                   |  1 +
>  4 files changed, 43 insertions(+), 3 deletions(-)
>
> diff --git a/fs/xattr.c b/fs/xattr.c
> index b3444e06cded..81847f132d26 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -16,6 +16,7 @@
>  #include <linux/namei.h>
>  #include <linux/security.h>
>  #include <linux/evm.h>
> +#include <linux/ima.h>
>  #include <linux/syscalls.h>
>  #include <linux/export.h>
>  #include <linux/fsnotify.h>
> @@ -502,6 +503,7 @@ __vfs_removexattr_locked(struct user_namespace *mnt_userns,
>  
>  	if (!error) {
>  		fsnotify_xattr(dentry);
> +		ima_inode_post_removexattr(dentry, name);
>  		evm_inode_post_removexattr(dentry, name);
>  	}
>  
> diff --git a/include/linux/ima.h b/include/linux/ima.h
> index 61d5723ec303..5e059da43857 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -171,7 +171,13 @@ extern void ima_inode_post_setattr(struct user_namespace *mnt_userns,
>  				   struct dentry *dentry);
>  extern int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
>  		       const void *xattr_value, size_t xattr_value_len);
> +extern void ima_inode_post_setxattr(struct dentry *dentry,
> +				    const char *xattr_name,
> +				    const void *xattr_value,
> +				    size_t xattr_value_len);
>  extern int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name);
> +extern void ima_inode_post_removexattr(struct dentry *dentry,
> +				       const char *xattr_name);
>  #else
>  static inline bool is_ima_appraise_enabled(void)
>  {
> @@ -192,11 +198,23 @@ static inline int ima_inode_setxattr(struct dentry *dentry,
>  	return 0;
>  }
>  
> +static inline void ima_inode_post_setxattr(struct dentry *dentry,
> +					   const char *xattr_name,
> +					   const void *xattr_value,
> +					   size_t xattr_value_len)
> +{
> +}
> +
>  static inline int ima_inode_removexattr(struct dentry *dentry,
>  					const char *xattr_name)
>  {
>  	return 0;
>  }
> +
> +static inline void ima_inode_post_removexattr(struct dentry *dentry,
> +					      const char *xattr_name)
> +{
> +}
>  #endif /* CONFIG_IMA_APPRAISE */
>  
>  #if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING)
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 565e33ff19d0..1f029e4c8d7f 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -577,21 +577,40 @@ int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
>  	if (result == 1) {
>  		if (!xattr_value_len || (xvalue->type >= IMA_XATTR_LAST))
>  			return -EINVAL;
> -		ima_reset_appraise_flags(d_backing_inode(dentry),
> -			xvalue->type == EVM_IMA_XATTR_DIGSIG);
>  		result = 0;
>  	}
>  	return result;
>  }
>  
> +void ima_inode_post_setxattr(struct dentry *dentry, const char *xattr_name,
> +			     const void *xattr_value, size_t xattr_value_len)
> +{
> +	const struct evm_ima_xattr_data *xvalue = xattr_value;
> +	int result;
> +
> +	result = ima_protect_xattr(dentry, xattr_name, xattr_value,
> +				   xattr_value_len);
> +	if (result == 1)
> +		ima_reset_appraise_flags(d_backing_inode(dentry),
> +			xvalue->type == EVM_IMA_XATTR_DIGSIG);
> +}
> +

Now you're calling ima_protect_xattr() twice for each setxattr.
Is that safe? Is it performant? Does it matter?

>  int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
>  {
>  	int result;
>  
>  	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
>  	if (result == 1) {
> -		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
>  		result = 0;
>  	}
>  	return result;
>  }
> +
> +void ima_inode_post_removexattr(struct dentry *dentry, const char *xattr_name)
> +{
> +	int result;
> +
> +	result = ima_protect_xattr(dentry, xattr_name, NULL, 0);
> +	if (result == 1)
> +		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
> +}

Now you're calling ima_protect_xattr() twice for each removexattr.
Is that safe? Is it performant? Does it matter?

> diff --git a/security/security.c b/security/security.c
> index 5ac96b16f8fa..efb1f874dc41 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1319,6 +1319,7 @@ void security_inode_post_setxattr(struct dentry *dentry, const char *name,
>  	if (unlikely(IS_PRIVATE(d_backing_inode(dentry))))
>  		return;
>  	call_void_hook(inode_post_setxattr, dentry, name, value, size, flags);
> +	ima_inode_post_setxattr(dentry, name, value, size);
>  	evm_inode_post_setxattr(dentry, name, value, size);
>  }
>  


  reply index

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-07 10:52 [PATCH v5 00/12] evm: Improve usability of portable signatures Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 01/12] evm: Execute evm_inode_init_security() only when an HMAC key is loaded Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 02/12] evm: Load EVM key in ima_load_x509() to avoid appraisal Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 03/12] evm: Refuse EVM_ALLOW_METADATA_WRITES only if an HMAC key is loaded Roberto Sassu
2021-04-30 20:28   ` Mimi Zohar
2021-04-07 10:52 ` [PATCH v5 04/12] ima: Move ima_reset_appraise_flags() call to post hooks Roberto Sassu
2021-04-07 16:17   ` Casey Schaufler [this message]
2021-04-07 16:31     ` Roberto Sassu
2021-04-26 19:49     ` Mimi Zohar
2021-04-07 10:52 ` [PATCH v5 05/12] evm: Introduce evm_status_revalidate() Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 06/12] evm: Ignore INTEGRITY_NOLABEL/INTEGRITY_NOXATTRS if conditions are safe Roberto Sassu
2021-05-03  0:12   ` Mimi Zohar
2021-05-03  7:55     ` Roberto Sassu
2021-05-03 12:07       ` Mimi Zohar
2021-05-03 14:15       ` Roberto Sassu
2021-05-03 14:34         ` Mimi Zohar
2021-05-04 13:16           ` Roberto Sassu
2021-05-04 13:45             ` Mimi Zohar
2021-04-07 10:52 ` [PATCH v5 07/12] evm: Allow xattr/attr operations for portable signatures Roberto Sassu
2021-05-03  0:12   ` Mimi Zohar
2021-05-04 14:28     ` Roberto Sassu
2021-05-04 14:49       ` Mimi Zohar
2021-04-07 10:52 ` [PATCH v5 08/12] evm: Pass user namespace to set/remove xattr hooks Roberto Sassu
2021-04-07 12:06   ` Christian Brauner
2021-04-07 10:52 ` [PATCH v5 09/12] evm: Allow setxattr() and setattr() for unmodified metadata Roberto Sassu
2021-04-07 12:05   ` Christian Brauner
2021-04-07 15:23   ` kernel test robot
2021-04-07 18:14   ` kernel test robot
2021-04-07 19:28     ` [RESEND][PATCH " Roberto Sassu
2021-05-03 13:00   ` [PATCH " Mimi Zohar
2021-05-03 14:48     ` Roberto Sassu
2021-05-03 15:13       ` Mimi Zohar
2021-05-03 15:30         ` Roberto Sassu
2021-05-03 15:11     ` Roberto Sassu
2021-05-03 15:26       ` Mimi Zohar
2021-05-03 15:32         ` Roberto Sassu
2021-05-03 15:48           ` Mimi Zohar
2021-04-07 10:52 ` [PATCH v5 10/12] ima: Allow imasig requirement to be satisfied by EVM portable signatures Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 11/12] ima: Introduce template field evmsig and write to field sig as fallback Roberto Sassu
2021-04-07 10:52 ` [PATCH v5 12/12] ima: Don't remove security.ima if file must not be appraised Roberto Sassu

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