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Message-ID: <a401e63a91114daba2037e2b0083101f@huawei.com>
Date: Wed, 2 Dec 2020 11:56:55 +0000
From: Roberto Sassu <roberto.sassu@...wei.com>
To: "zohar@...ux.ibm.com" <zohar@...ux.ibm.com>,
"mjg59@...gle.com" <mjg59@...gle.com>
CC: "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
"linux-security-module@...r.kernel.org"
<linux-security-module@...r.kernel.org>,
"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Silviu Vlasceanu <Silviu.Vlasceanu@...wei.com>
Subject: RE: [PATCH v3 04/11] ima: Move ima_reset_appraise_flags() call to
post hooks
> 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@...wei.com>
> ---
> 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
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