[PATCH 3/5] ima: Reset EVM status upon detecting changes to overlay backing file

Stefan Berger
2024-01-30T21:46:52Z

To avoid caching effects to take effect reset the EVM status upon
detecting changes to the overlay backing files. This prevents a not-yet-
copied-up file on the overlay from executing if for example the
security.evm xattr on the file on the 'lower' layer has been removed.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
include/linux/evm.h | 8 ++++++++
security/integrity/evm/evm_main.c | 7 +++++++
security/integrity/ima/ima_main.c | 2 ++
3 files changed, 17 insertions(+)

diff --git a/include/linux/evm.h b/include/linux/evm.h
index d8c0343436b8..e7d6742eee9d 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -66,6 +66,8 @@ extern int evm_protected_xattr_if_enabled(const char *req_xattr_name);
extern int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
int buffer_size, char type,
bool canonical_fmt);
+extern void evm_reset_cache_status(struct dentry *dentry,
+ struct integrity_iint_cache *iint);
#ifdef CONFIG_FS_POSIX_ACL
extern int posix_xattr_acl(const char *xattrname);
#else
@@ -189,5 +191,11 @@ static inline int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
return -EOPNOTSUPP;
}

+static inline void evm_reset_cache_status(struct dentry *dentry,
+ struct integrity_iint_cache *iint)
+{
+ return;
+}
+
#endif /* CONFIG_EVM */
#endif /* LINUX_EVM_H */
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 22a5e26860ea..e96d127b48a2 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -721,6 +721,13 @@ static void evm_reset_status(struct inode *inode)
iint->evm_status = INTEGRITY_UNKNOWN;
}

+void evm_reset_cache_status(struct dentry *dentry,
+ struct integrity_iint_cache *iint)
+{
+ if (d_real_inode(dentry) != d_backing_inode(dentry))
+ iint->evm_status = INTEGRITY_UNKNOWN;
+}
+
/**
* evm_revalidate_status - report whether EVM status re-validation is necessary
* @xattr_name: pointer to the affected extended attribute name
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index cc1217ac2c6f..84bdc6e58329 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -26,6 +26,7 @@
#include <linux/ima.h>
#include <linux/fs.h>
#include <linux/iversion.h>
+#include <linux/evm.h>

#include "ima.h"

@@ -295,6 +296,7 @@ static int process_measurement(struct file *file, const struct cred *cred,
!inode_eq_iversion(backing_inode, iint->version)) {
iint->flags &= ~IMA_DONE_MASK;
iint->measured_pcrs = 0;
+ evm_reset_cache_status(file_dentry(file), iint);
}
}

--
2.43.0