RE: [PATCH v3 04/11] ima: Move ima_reset_appraise_flags() call to post hooks

[Roberto Sassu]

> From: Roberto Sassu
> Sent: Wednesday, November 11, 2020 10:23 AM
> 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(), removes ima_inode_removexattr() and
> adds the
> call to ima_reset_appraise_flags() in the new functions.

Removing ima_inode_removexattr() is not correct. We should still prevent
that security.ima is removed when CAP_SYS_ADMIN is not set. I will fix
this in the next version.

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> ---
>  fs/xattr.c                            |  2 ++
>  include/linux/ima.h                   | 19 +++++++++++++++----
>  security/integrity/ima/ima_appraise.c | 22 +++++++++++++++-------
>  security/security.c                   |  4 +---
>  4 files changed, 33 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/xattr.c b/fs/xattr.c
> index cd7a563e8bcd..149b8cf5f99f 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>
> @@ -474,6 +475,7 @@ __vfs_removexattr_locked(struct dentry *dentry,
> const char *name,
> 
>  	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 ac3d82f962f2..19a775fa2ba5 100644
> --- a/include/linux/ima.h
> +++ b/include/linux/ima.h
> @@ -150,7 +150,12 @@ extern bool is_ima_appraise_enabled(void);
>  extern void ima_inode_post_setattr(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 int ima_inode_removexattr(struct dentry *dentry, const char
> *xattr_name);
> +extern void ima_inode_post_setxattr(struct dentry *dentry,
> +				    const char *xattr_name,
> +				    const void *xattr_value,
> +				    size_t xattr_value_len);
> +extern void ima_inode_post_removexattr(struct dentry *dentry,
> +				       const char *xattr_name);
>  #else
>  static inline bool is_ima_appraise_enabled(void)
>  {
> @@ -170,10 +175,16 @@ static inline int ima_inode_setxattr(struct dentry
> *dentry,
>  	return 0;
>  }
> 
> -static inline int ima_inode_removexattr(struct dentry *dentry,
> -					const char *xattr_name)
> +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 void ima_inode_post_removexattr(struct dentry *dentry,
> +					      const char *xattr_name)
>  {
> -	return 0;
>  }
>  #endif /* CONFIG_IMA_APPRAISE */
> 
> diff --git a/security/integrity/ima/ima_appraise.c
> b/security/integrity/ima/ima_appraise.c
> index 8361941ee0a1..77c01f50425e 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -574,21 +574,29 @@ 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;
>  }
> 
> -int ima_inode_removexattr(struct dentry *dentry, const char *xattr_name)
> +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);
> +}
> +
> +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) {
> +	if (result == 1)
>  		ima_reset_appraise_flags(d_backing_inode(dentry), 0);
> -		result = 0;
> -	}
> -	return result;
>  }
> diff --git a/security/security.c b/security/security.c
> index a28045dc9e7f..fc43f45938b4 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1309,6 +1309,7 @@ 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);
>  }
> 
> @@ -1339,9 +1340,6 @@ int security_inode_removexattr(struct dentry
> *dentry, const char *name)
>  	ret = call_int_hook(inode_removexattr, 1, dentry, name);
>  	if (ret == 1)
>  		ret = cap_inode_removexattr(dentry, name);
> -	if (ret)
> -		return ret;
> -	ret = ima_inode_removexattr(dentry, name);
>  	if (ret)
>  		return ret;
>  	return evm_inode_removexattr(dentry, name);
> --
> 2.27.GIT