signal: Distinguish between kernel_siginfo and siginfo

Linus recently observed that if we did not worry about the padding
member in struct siginfo it is only about 48 bytes, and 48 bytes is
much nicer than 128 bytes for allocating on the stack and copying
around in the kernel.

The obvious thing of only adding the padding when userspace is
including siginfo.h won't work as there are sigframe definitions in
the kernel that embed struct siginfo.

So split siginfo in two; kernel_siginfo and siginfo.  Keeping the
traditional name for the userspace definition.  While the version that
is used internally to the kernel and ultimately will not be padded to
128 bytes is called kernel_siginfo.

The definition of struct kernel_siginfo I have put in include/signal_types.h

A set of buildtime checks has been added to verify the two structures have
the same field offsets.

To make it easy to verify the change kernel_siginfo retains the same
size as siginfo.  The reduction in size comes in a following change.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 97a020c616ad..bb40f6d34163 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -672,7 +672,7 @@
  *      Return 0 if permission is granted.
  * @task_kill:
  *      Check permission before sending signal @sig to @p.  @info can be NULL,
- *      the constant 1, or a pointer to a siginfo structure.  If @info is 1 or
+ *      the constant 1, or a pointer to a kernel_siginfo structure.  If @info is 1 or
  *      SI_FROMKERNEL(info) is true, then the signal should be viewed as coming
  *      from the kernel and should typically be permitted.
  *      SIGIO signals are handled separately by the send_sigiotask hook in
@@ -1606,7 +1606,7 @@ union security_list_options {
         int (*task_setscheduler)(struct task_struct *p);
         int (*task_getscheduler)(struct task_struct *p);
         int (*task_movememory)(struct task_struct *p);
-        int (*task_kill)(struct task_struct *p, struct siginfo *info,
+        int (*task_kill)(struct task_struct *p, struct kernel_siginfo *info,
                                 int sig, const struct cred *cred);
         int (*task_prctl)(int option, unsigned long arg2, unsigned long arg3,
                                 unsigned long arg4, unsigned long arg5);