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>

diff --git a/drivers/base/firmware_loader/fallback.c b/drivers/base/firmware_loader/fallback.c
index 283ca2de76d45ea26a772c4b9330a61580ba269b..bff4717cc6b5e0c9bbb4ac4c14c131aad6c0f1a8 100644 (file)
--- 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 6958ab1a80593357308009c89a738c7dd061c2d5..a12c79d47efc21a85b94ee8584715690f2a5fbaf 100644 (file)
--- 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 64804f78408b8454b2130f8c5ea0c7d1a2c5434a..af9fb8c5f16a7eabfc2929b11327331818d85c22 100644 (file)
--- 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, 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;
 }

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index 2a8c74d99015b6900b47c43ff0a4ab14dccc43de..83c6f1f5cc1e8d08f8a66691d4e613f88273e93d 100644 (file)
--- 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, 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,

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 9e2e3e63719df1e3e8a85205ac26eee16b970f9a..6bb4f1a0158cd5b01fbd1db3f0f2c0f42006ca03 100644 (file)
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -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

diff --git a/include/linux/security.h b/include/linux/security.h
index 42df0d9b4c37b24f6036f3be5f3e0d5198b72cc7..51c8e4e6b7cc0caf25abadf326e9b7d38adfb574 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -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;
 }

diff --git a/kernel/kexec.c b/kernel/kexec.c
index f977786fe498fb7241337c6da0e94e3a0ad85d34..c82c6c06f0518f3591de33431904d60175e69bc2 100644 (file)
--- 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 0f11eaed047e4f8700e60628731b63f51ff4962b..f47209e0fde6dadc5ee5ddc331613417b569cbe3 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -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;
 

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 5f89970c5ab7d0205972a72637fb6c07a98ffa62..9dd9c5f4d7361152017be4aef51e4b1b73affd7c 100644 (file)
--- 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 +725,26 @@ 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)

diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index 163c48216d13eadfe9bdf270e17079368309f98a..28782412febb5d325db1dbcb5e0df21da73ed6bd 100644 (file)
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -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);
 }

diff --git a/security/security.c b/security/security.c
index 19d3150f68f483b6eed9d1462ada89c7e3cc28a2..531b855826fc36e3220592ea445fef8514ac933a 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -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)
 {

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 96f5f8b3b9f038b33bc8cc1900d09e83d807c0b8..558beee97d8de7942ba246f670996152c5d90a8f 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -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;