vfs: define a generic function to read a file from the kernel

For a while it was looked down upon to directly read files from Linux.
These days there exists a few mechanisms in the kernel that do just
this though to load a file into a local buffer.  There are minor but
important checks differences on each.  This patch set is the first
attempt at resolving some of these differences.

This patch introduces a common function for reading files from the kernel
with the corresponding security post-read hook and function.

Changelog v4+:
- export security_kernel_post_read_file() - Fengguang Wu
v3:
- additional bounds checking - Luis
v2:
- To simplify patch review, re-ordered patches

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Reviewed-by: Luis R. Rodriguez <mcgrof@suse.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 8 insertions, 0 deletions

diff --git a/security/security.c b/security/security.c
index e8ffd92ae2eb..c98dd6bf4ebd 100644
--- a/security/security.c
+++ b/security/security.c
@@ -910,6 +910,12 @@ int security_kernel_module_from_file(struct file *file)
         return ima_module_check(file);
 }
 
+int security_kernel_post_read_file(struct file *file, char *buf, loff_t size)
+{
+        return call_int_hook(kernel_post_read_file, 0, file, buf, size);
+}
+EXPORT_SYMBOL_GPL(security_kernel_post_read_file);
+
 int security_task_fix_setuid(struct cred *new, const struct cred *old,
                              int flags)
 {
@@ -1697,6 +1703,8 @@ struct security_hook_heads security_hook_heads = {
                 LIST_HEAD_INIT(security_hook_heads.kernel_module_request),
         .kernel_module_from_file =
                 LIST_HEAD_INIT(security_hook_heads.kernel_module_from_file),
+        .kernel_post_read_file =
+                LIST_HEAD_INIT(security_hook_heads.kernel_post_read_file),
         .task_fix_setuid =
                 LIST_HEAD_INIT(security_hook_heads.task_fix_setuid),
         .task_setpgid = LIST_HEAD_INIT(security_hook_heads.task_setpgid),