[PATCH v3 15/25] security: Introduce file_pre_free_security hook

Roberto Sassu
2023-09-04T13:39:03Z

From: Roberto Sassu <roberto.sassu@huawei.com>

In preparation for moving IMA and EVM to the LSM infrastructure, introduce
the file_pre_free_security hook.

It is useful for IMA to calculate the digest of the file content, just
before a file descriptor is closed, and update the security.ima xattr with
the new value.

LSMs should use this hook instead of file_free_security, if they still need
to access the opened file, before it is closed. The new hook cannot return
an error and cannot cause the operation to be canceled.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
fs/file_table.c | 1 +
include/linux/lsm_hook_defs.h | 1 +
include/linux/security.h | 4 ++++
security/security.c | 11 +++++++++++
4 files changed, 17 insertions(+)

diff --git a/fs/file_table.c b/fs/file_table.c
index fc7d677ff5ad..964e24120684 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -375,6 +375,7 @@ static void __fput(struct file *file)
eventpoll_release(file);
locks_remove_file(file);

+ security_file_pre_free(file);
ima_file_free(file);
if (unlikely(file->f_flags & FASYNC)) {
if (file->f_op->fasync)
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 60ed33f0c80d..797f51da3f7d 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -172,6 +172,7 @@ LSM_HOOK(int, 0, kernfs_init_security, struct kernfs_node *kn_dir,
struct kernfs_node *kn)
LSM_HOOK(int, 0, file_permission, struct file *file, int mask)
LSM_HOOK(int, 0, file_alloc_security, struct file *file)
+LSM_HOOK(void, LSM_RET_VOID, file_pre_free_security, struct file *file)
LSM_HOOK(void, LSM_RET_VOID, file_free_security, struct file *file)
LSM_HOOK(int, 0, file_ioctl, struct file *file, unsigned int cmd,
unsigned long arg)
diff --git a/include/linux/security.h b/include/linux/security.h
index a0f16511c059..7871009d59ae 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -389,6 +389,7 @@ int security_kernfs_init_security(struct kernfs_node *kn_dir,
struct kernfs_node *kn);
int security_file_permission(struct file *file, int mask);
int security_file_alloc(struct file *file);
+void security_file_pre_free(struct file *file);
void security_file_free(struct file *file);
int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
int security_mmap_file(struct file *file, unsigned long prot,
@@ -985,6 +986,9 @@ static inline int security_file_alloc(struct file *file)
return 0;
}

+static inline void security_file_pre_free(struct file *file)
+{ }
+
static inline void security_file_free(struct file *file)
{ }

diff --git a/security/security.c b/security/security.c
index 3e0078b51e46..fbb58eeeea02 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2626,6 +2626,17 @@ int security_file_alloc(struct file *file)
return rc;
}

+/**
+ * security_file_pre_free() - Perform actions before closing a file descriptor
+ * @file: the file
+ *
+ * Perform actions before the file descriptor is closed and freed.
+ */
+void security_file_pre_free(struct file *file)
+{
+ call_void_hook(file_pre_free_security, file);
+}
+
/**
* security_file_free() - Free a file's LSM blob
* @file: the file
--
2.34.1