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>

4 files changed, 4 insertions, 4 deletions

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 8b8b70620bbe..cbcb8ba51142 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -732,7 +732,7 @@ static int apparmor_task_setrlimit(struct task_struct *task,
         return error;
 }
 
-static int apparmor_task_kill(struct task_struct *target, struct siginfo *info,
+static int apparmor_task_kill(struct task_struct *target, struct kernel_siginfo *info,
                               int sig, const struct cred *cred)
 {
         struct aa_label *cl, *tl;
diff --git a/security/security.c b/security/security.c
index 736e78da1ab9..0d504fceda8b 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1147,7 +1147,7 @@ int security_task_movememory(struct task_struct *p)
         return call_int_hook(task_movememory, 0, 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)
 {
         return call_int_hook(task_kill, 0, p, info, sig, cred);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index ad9a9b8e9979..1b500b4c78a7 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -4186,7 +4186,7 @@ static int selinux_task_movememory(struct task_struct *p)
                             PROCESS__SETSCHED, NULL);
 }
 
-static int selinux_task_kill(struct task_struct *p, struct siginfo *info,
+static int selinux_task_kill(struct task_struct *p, struct kernel_siginfo *info,
                                 int sig, const struct cred *cred)
 {
         u32 secid;
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 340fc30ad85d..025de76af1db 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -2251,7 +2251,7 @@ static int smack_task_movememory(struct task_struct *p)
  * Return 0 if write access is permitted
  *
  */
-static int smack_task_kill(struct task_struct *p, struct siginfo *info,
+static int smack_task_kill(struct task_struct *p, struct kernel_siginfo *info,
                            int sig, const struct cred *cred)
 {
         struct smk_audit_info ad;