LSM: Introduce kernel_post_load_data() hook

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>
Reviewed-by: KP Singh <kpsingh@google.com>
Link: https://lore.kernel.org/r/20201002173828.2099543-9-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Kees Cook 2020-10-02 10:38:20 -07:00 committed by Greg Kroah-Hartman
parent 885352881f
commit b64fcae74b
12 changed files with 82 additions and 15 deletions

View File

@ -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;

View File

@ -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;

View File

@ -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, char *description);
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 +80,14 @@ 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,
char *description)
{
return 0;
}

View File

@ -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, char *description)
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,

View File

@ -635,7 +635,17 @@
* @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
* @description a text description of what was loaded, @id-specific
* 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

View File

@ -387,7 +387,10 @@ 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,
char *description);
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 +1017,14 @@ 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,
char *description)
{
return 0;
}

View File

@ -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;

View File

@ -3014,7 +3014,7 @@ 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;

View File

@ -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 +725,26 @@ 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
* @description: @id-specific description of contents
*
* 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,
char *description)
{
return 0;
}
/*
* process_buffer_measurement - Measure the buffer to ima log.
* @inode: inode associated with the object being measured (NULL for KEY_CHECK)

View File

@ -177,7 +177,7 @@ 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);
}

View File

@ -1695,17 +1695,31 @@ 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,
char *description)
{
int ret;
ret = call_int_hook(kernel_post_load_data, 0, buf, size, id,
description);
if (ret)
return ret;
return ima_post_load_data(buf, size, id, description);
}
EXPORT_SYMBOL_GPL(security_kernel_post_load_data);
int security_task_fix_setuid(struct cred *new, const struct cred *old,
int flags)
{

View File

@ -4018,7 +4018,7 @@ 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;