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Subject[PATCH v2 08/11] ima: add ima_inode_setxattr/removexattr function and calls
Date
Based on xattr_permission comments, the restriction to modify 'security'
xattr is left up to the underlying fs or lsm. Ensure that not just anyone
can modify or remove 'security.ima'.

Changelog v1:
- Unless IMA-APPRAISE is configured, use stub ima_inode_removexattr()/setxattr()
functions. (Moved ima_inode_removexattr()/setxattr() to ima_appraise.c)

Changelog:
- take i_mutex to fix locking (Dmitry Kasatkin)
- ima_reset_appraise_flags should only be called when modifying or
removing the 'security.ima' xattr. Requires CAP_SYS_ADMIN privilege.
(Incorporated fix from Roberto Sassu)
- Even if allowed to update security.ima, reset the appraisal flags,
forcing re-appraisal.
- Replace CAP_MAC_ADMIN with CAP_SYS_ADMIN
- static inline ima_inode_setxattr()/ima_inode_removexattr() stubs
- ima_protect_xattr should be static

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
---
include/linux/ima.h | 17 ++++++++++
security/integrity/ima/ima_appraise.c | 57 +++++++++++++++++++++++++++++++++
security/security.c | 6 +++
3 files changed, 80 insertions(+), 0 deletions(-)
diff --git a/include/linux/ima.h b/include/linux/ima.h
index e2bfbb1..2c7223d 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -44,10 +44,27 @@ static inline int ima_file_mmap(struct file *file, unsigned long prot)

#ifdef CONFIG_IMA_APPRAISE
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);
#else
static inline void ima_inode_post_setattr(struct dentry *dentry)
{
return;
}
+
+static inline int ima_inode_setxattr(struct dentry *dentry,
+ const char *xattr_name,
+ const void *xattr_value,
+ size_t xattr_value_len)
+{
+ return 0;
+}
+
+static inline int ima_inode_removexattr(struct dentry *dentry,
+ const char *xattr_name)
+{
+ return 0;
+}
#endif /* CONFIG_IMA_APPRAISE_H */
#endif /* _LINUX_IMA_H */
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 0fd7ec3..a29eb03 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -166,3 +166,60 @@ void ima_inode_post_setattr(struct dentry *dentry)
rc = inode->i_op->removexattr(dentry, XATTR_NAME_IMA);
return;
}
+
+/*
+ * ima_protect_xattr - protect 'security.ima'
+ *
+ * Ensure that not just anyone can modify or remove 'security.ima'.
+ */
+static int ima_protect_xattr(struct dentry *dentry, const char *xattr_name,
+ const void *xattr_value, size_t xattr_value_len)
+{
+ if (strcmp(xattr_name, XATTR_NAME_IMA) == 0) {
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ return 1;
+ }
+ return 0;
+}
+
+static void ima_reset_appraise_flags(struct inode *inode)
+{
+ struct integrity_iint_cache *iint;
+
+ if (!ima_initialized || !ima_appraise || !S_ISREG(inode->i_mode))
+ return;
+
+ iint = integrity_iint_find(inode);
+ if (!iint)
+ return;
+
+ iint->flags &= ~(IMA_COLLECTED | IMA_APPRAISED | IMA_MEASURED);
+ return;
+}
+
+int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
+ const void *xattr_value, size_t xattr_value_len)
+{
+ int result;
+
+ result = ima_protect_xattr(dentry, xattr_name, xattr_value,
+ xattr_value_len);
+ if (result == 1) {
+ ima_reset_appraise_flags(dentry->d_inode);
+ result = 0;
+ }
+ return result;
+}
+
+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(dentry->d_inode);
+ result = 0;
+ }
+ return result;
+}
diff --git a/security/security.c b/security/security.c
index e50bbf4..7bb127e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -557,6 +557,9 @@ int security_inode_setxattr(struct dentry *dentry, const char *name,
ret = security_ops->inode_setxattr(dentry, name, value, size, flags);
if (ret)
return ret;
+ ret = ima_inode_setxattr(dentry, name, value, size);
+ if (ret)
+ return ret;
return evm_inode_setxattr(dentry, name, value, size);
}

@@ -592,6 +595,9 @@ int security_inode_removexattr(struct dentry *dentry, const char *name)
ret = security_ops->inode_removexattr(dentry, name);
if (ret)
return ret;
+ ret = ima_inode_removexattr(dentry, name);
+ if (ret)
+ return ret;
return evm_inode_removexattr(dentry, name);
}

--
1.7.6.5


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