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/kernel/seccomp.c b/kernel/seccomp.c
index fd023ac24e10..4d7809cdd27d 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -522,7 +522,7 @@ void put_seccomp_filter(struct task_struct *tsk)
         __put_seccomp_filter(tsk->seccomp.filter);
 }
 
-static void seccomp_init_siginfo(siginfo_t *info, int syscall, int reason)
+static void seccomp_init_siginfo(kernel_siginfo_t *info, int syscall, int reason)
 {
         clear_siginfo(info);
         info->si_signo = SIGSYS;
@@ -542,7 +542,7 @@ static void seccomp_init_siginfo(siginfo_t *info, int syscall, int reason)
  */
 static void seccomp_send_sigsys(int syscall, int reason)
 {
-        struct siginfo info;
+        struct kernel_siginfo info;
         seccomp_init_siginfo(&info, syscall, reason);
         force_sig_info(SIGSYS, &info, current);
 }
@@ -747,7 +747,7 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
                 /* Dump core only if this is the last remaining thread. */
                 if (action == SECCOMP_RET_KILL_PROCESS ||
                     get_nr_threads(current) == 1) {
-                        siginfo_t info;
+                        kernel_siginfo_t info;
 
                         /* Show the original registers in the dump. */
                         syscall_rollback(current, task_pt_regs(current));