[PATCH v2 11/18] LSM: Introduce kernel_post_load_data() hook

Kees Cook
2020-07-22T19:39:23Z

There are a few places in the kernel where LSMs would like to have
visibility into the contents of a kernel buffer that has been loaded or
read. While security_kernel_post_read_file() (which includes the
buffer) exists as a pairing for security_kernel_read_file(), no such
hook exists to pair with security_kernel_load_data().

Earlier proposals for just using security_kernel_post_read_file() with a
NULL file argument were rejected (i.e. "file" should always be valid for
the security_..._file hooks, but it appears at least one case was
left in the kernel during earlier refactoring. (This will be fixed in
a subsequent patch.)

Since not all cases of security_kernel_load_data() can have a single
contiguous buffer made available to the LSM hook (e.g. kexec image
segments are separately loaded), there needs to be a way for the LSM to
reason about its expectations of the hook coverage. In order to handle
this, add a "contents" argument to the "kernel_load_data" hook that
indicates if the newly added "kernel_post_load_data" hook will be called
with the full contents once loaded. That way, LSMs requiring full contents
can choose to unilaterally reject "kernel_load_data" with contents=false
(which is effectively the existing hook coverage), but when contents=true
they can allow it and later evaluate the "kernel_post_load_data" hook
once the buffer is loaded.

With this change, LSMs can gain coverage over non-file-backed data loads
(e.g. init_module(2) and firmware userspace helper), which will happen
in subsequent patches.

Additionally prepare IMA to start processing these cases.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/base/firmware_loader/fallback.c | 2 +-
.../base/firmware_loader/fallback_platform.c | 2 +-
include/linux/ima.h | 12 +++++++++--
include/linux/lsm_hook_defs.h | 4 +++-
include/linux/lsm_hooks.h | 9 ++++++++
include/linux/security.h | 12 +++++++++--
kernel/kexec.c | 2 +-
kernel/module.c | 2 +-
security/integrity/ima/ima_main.c | 21 ++++++++++++++++++-
security/loadpin/loadpin.c | 2 +-
security/security.c | 18 +++++++++++++---
security/selinux/hooks.c | 2 +-
12 files changed, 73 insertions(+), 15 deletions(-)

diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c
index 5327bfc6ba71..a196aacce22c 100644
--- a/drivers/base/firmware_loader/fallback.c
+++ b/drivers/base/firmware_loader/fallback.c
@@ -613,7 +613,7 @@ static bool fw_run_sysfs_fallback(u32 opt_flags)
return false;

/* Also permit LSMs and IMA to fail firmware sysfs fallback */
- ret = security_kernel_load_data(LOADING_FIRMWARE);
+ ret = security_kernel_load_data(LOADING_FIRMWARE, false);
if (ret < 0)
return false;

diff --git a/drivers/base/firmware_loader/fallback_platform.c b/drivers/base/firmware_loader/fallback_platform.c
index 6958ab1a8059..a12c79d47efc 100644
--- a/drivers/base/firmware_loader/fallback_platform.c
+++ b/drivers/base/firmware_loader/fallback_platform.c
@@ -17,7 +17,7 @@ int firmware_fallback_platform(struct fw_priv *fw_priv, u32 opt_flags)
if (!(opt_flags & FW_OPT_FALLBACK_PLATFORM))
return -ENOENT;

- rc = security_kernel_load_data(LOADING_FIRMWARE);
+ rc = security_kernel_load_data(LOADING_FIRMWARE, false);
if (rc)
return rc;

diff --git a/include/linux/ima.h b/include/linux/ima.h
index 148636bfcc8f..502e36ad7804 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -20,7 +20,9 @@ extern void ima_post_create_tmpfile(struct inode *inode);
extern void ima_file_free(struct file *file);
extern int ima_file_mmap(struct file *file, unsigned long prot);
extern int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot);
-extern int ima_load_data(enum kernel_load_data_id id);
+extern int ima_load_data(enum kernel_load_data_id id, bool contents);
+extern int ima_post_load_data(char *buf, loff_t size,
+ enum kernel_load_data_id id);
extern int ima_read_file(struct file *file, enum kernel_read_file_id id);
extern int ima_post_read_file(struct file *file, void *buf, loff_t size,
enum kernel_read_file_id id);
@@ -78,7 +80,13 @@ static inline int ima_file_mprotect(struct vm_area_struct *vma,
return 0;
}

-static inline int ima_load_data(enum kernel_load_data_id id)
+static inline int ima_load_data(enum kernel_load_data_id id, bool contents)
+{
+ return 0;
+}
+
+static inline int ima_post_load_data(char *buf, loff_t size,
+ enum kernel_load_data_id id)
{
return 0;
}
diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 6791813cd439..aaa2916bbae7 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -184,7 +184,9 @@ LSM_HOOK(void, LSM_RET_VOID, cred_getsecid, const struct cred *c, u32 *secid)
LSM_HOOK(int, 0, kernel_act_as, struct cred *new, u32 secid)
LSM_HOOK(int, 0, kernel_create_files_as, struct cred *new, struct inode *inode)
LSM_HOOK(int, 0, kernel_module_request, char *kmod_name)
-LSM_HOOK(int, 0, kernel_load_data, enum kernel_load_data_id id)
+LSM_HOOK(int, 0, kernel_load_data, enum kernel_load_data_id id, bool contents)
+LSM_HOOK(int, 0, kernel_post_load_data, char *buf, loff_t size,
+ enum kernel_read_file_id id)
LSM_HOOK(int, 0, kernel_read_file, struct file *file,
enum kernel_read_file_id id)
LSM_HOOK(int, 0, kernel_post_read_file, struct file *file, char *buf,
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 95b7c1d32062..812d626195fc 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -635,7 +635,16 @@
* @kernel_load_data:
* Load data provided by userspace.
* @id kernel load data identifier
+ * @contents if a subsequent @kernel_post_load_data will be called.
* Return 0 if permission is granted.
+ * @kernel_post_load_data:
+ * Load data provided by a non-file source (usually userspace buffer).
+ * @buf pointer to buffer containing the data contents.
+ * @size length of the data contents.
+ * @id kernel load data identifier
+ * Return 0 if permission is granted.
+ * This must be paired with a prior @kernel_load_data call that had
+ * @contents set to true.
* @kernel_read_file:
* Read a file specified by userspace.
* @file contains the file structure pointing to the file being read
diff --git a/include/linux/security.h b/include/linux/security.h
index 42df0d9b4c37..e748974c707b 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -387,7 +387,9 @@ void security_cred_getsecid(const struct cred *c, u32 *secid);
int security_kernel_act_as(struct cred *new, u32 secid);
int security_kernel_create_files_as(struct cred *new, struct inode *inode);
int security_kernel_module_request(char *kmod_name);
-int security_kernel_load_data(enum kernel_load_data_id id);
+int security_kernel_load_data(enum kernel_load_data_id id, bool contents);
+int security_kernel_post_load_data(char *buf, loff_t size,
+ enum kernel_load_data_id id);
int security_kernel_read_file(struct file *file, enum kernel_read_file_id id);
int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
enum kernel_read_file_id id);
@@ -1014,7 +1016,13 @@ static inline int security_kernel_module_request(char *kmod_name)
return 0;
}

-static inline int security_kernel_load_data(enum kernel_load_data_id id)
+static inline int security_kernel_load_data(enum kernel_load_data_id id, bool contents)
+{
+ return 0;
+}
+
+static inline int security_kernel_post_load_data(char *buf, loff_t size,
+ enum kernel_load_data_id id)
{
return 0;
}
diff --git a/kernel/kexec.c b/kernel/kexec.c
index f977786fe498..c82c6c06f051 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -205,7 +205,7 @@ static inline int kexec_load_check(unsigned long nr_segments,
return -EPERM;

/* Permit LSMs and IMA to fail the kexec */
- result = security_kernel_load_data(LOADING_KEXEC_IMAGE);
+ result = security_kernel_load_data(LOADING_KEXEC_IMAGE, false);
if (result < 0)
return result;

diff --git a/kernel/module.c b/kernel/module.c
index 860d713dd910..d56cb34d9a2f 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2967,7 +2967,7 @@ static int copy_module_from_user(const void __user *umod, unsigned long len,
if (info->len < sizeof(*(info->hdr)))
return -ENOEXEC;

- err = security_kernel_load_data(LOADING_MODULE);
+ err = security_kernel_load_data(LOADING_MODULE, false);
if (err)
return err;

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index dab4a13221cf..85000dc8595c 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -676,6 +676,8 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
/**
* ima_load_data - appraise decision based on policy
* @id: kernel load data caller identifier
+ * @contents: whether the full contents will be available in a later
+ * call to ima_post_load_data().
*
* Callers of this LSM hook can not measure, appraise, or audit the
* data provided by userspace. Enforce policy rules requring a file
@@ -683,7 +685,7 @@ int ima_post_read_file(struct file *file, void *buf, loff_t size,
*
* For permission return 0, otherwise return -EACCES.
*/
-int ima_load_data(enum kernel_load_data_id id)
+int ima_load_data(enum kernel_load_data_id id, bool contents)
{
bool ima_enforce, sig_enforce;

@@ -723,6 +725,23 @@ int ima_load_data(enum kernel_load_data_id id)
return 0;
}

+/**
+ * ima_post_load_data - appraise decision based on policy
+ * @buf: pointer to in memory file contents
+ * @size: size of in memory file contents
+ * @id: kernel load data caller identifier
+ *
+ * Measure/appraise/audit in memory buffer based on policy. Policy rules
+ * are written in terms of a policy identifier.
+ *
+ * On success return 0. On integrity appraisal error, assuming the file
+ * is in policy and IMA-appraisal is in enforcing mode, return -EACCES.
+ */
+int ima_post_load_data(char *buf, loff_t size, enum kernel_load_data_id load_id)
+{
+ return 0;
+}
+
/*
* process_buffer_measurement - Measure the buffer to ima log.
* @buf: pointer to the buffer that needs to be added to the log.
diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index 81bc95127f92..db320a43f42e 100644
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -176,7 +176,7 @@ static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
return 0;
}

-static int loadpin_load_data(enum kernel_load_data_id id)
+static int loadpin_load_data(enum kernel_load_data_id id, bool contents)
{
return loadpin_read_file(NULL, (enum kernel_read_file_id) id);
}
diff --git a/security/security.c b/security/security.c
index f5920115a325..090674f1197a 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1680,17 +1680,29 @@ int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
}
EXPORT_SYMBOL_GPL(security_kernel_post_read_file);

-int security_kernel_load_data(enum kernel_load_data_id id)
+int security_kernel_load_data(enum kernel_load_data_id id, bool contents)
{
int ret;

- ret = call_int_hook(kernel_load_data, 0, id);
+ ret = call_int_hook(kernel_load_data, 0, id, contents);
if (ret)
return ret;
- return ima_load_data(id);
+ return ima_load_data(id, contents);
}
EXPORT_SYMBOL_GPL(security_kernel_load_data);

+int security_kernel_post_load_data(char *buf, loff_t size,
+ enum kernel_load_data_id id)
+{
+ int ret;
+
+ ret = call_int_hook(kernel_post_load_data, 0, buf, size, id);
+ if (ret)
+ return ret;
+ return ima_post_load_data(buf, size, id);
+}
+EXPORT_SYMBOL_GPL(security_kernel_post_load_data);
+
int security_task_fix_setuid(struct cred *new, const struct cred *old,
int flags)
{
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 5de45010fb1a..1a5c68196faf 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4019,7 +4019,7 @@ static int selinux_kernel_read_file(struct file *file,
return rc;
}

-static int selinux_kernel_load_data(enum kernel_load_data_id id)
+static int selinux_kernel_load_data(enum kernel_load_data_id id, bool contents)
{
int rc = 0;