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, 3 insertions, 3 deletions

diff --git a/include/linux/security.h b/include/linux/security.h
index 75f4156c84d7..d170a5b031f3 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -35,7 +35,7 @@
 struct linux_binprm;
 struct cred;
 struct rlimit;
-struct siginfo;
+struct kernel_siginfo;
 struct sembuf;
 struct kern_ipc_perm;
 struct audit_context;
@@ -361,7 +361,7 @@ int security_task_setrlimit(struct task_struct *p, unsigned int resource,
 int security_task_setscheduler(struct task_struct *p);
 int security_task_getscheduler(struct task_struct *p);
 int security_task_movememory(struct task_struct *p);
-int security_task_kill(struct task_struct *p, struct siginfo *info,
+int security_task_kill(struct task_struct *p, struct kernel_siginfo *info,
                         int sig, const struct cred *cred);
 int security_task_prctl(int option, unsigned long arg2, unsigned long arg3,
                         unsigned long arg4, unsigned long arg5);
@@ -1020,7 +1020,7 @@ static inline int security_task_movememory(struct task_struct *p)
 }
 
 static inline int security_task_kill(struct task_struct *p,
-                                     struct siginfo *info, int sig,
+                                     struct kernel_siginfo *info, int sig,
                                      const struct cred *cred)
 {
         return 0;