signals: SEND_SIG_NOINFO should be considered as SI_FROMUSER()

No changes in compiled code. The patch adds the new helper, si_fromuser()
and changes check_kill_permission() to use this helper.

The real effect of this patch is that from now we "officially" consider
SEND_SIG_NOINFO signal as "from user-space" signals. This is already true
if we look at the code which uses SEND_SIG_NOINFO, except __send_signal()
has another opinion - see the next patch.

The naming of these special SEND_SIG_XXX siginfo's is really bad
imho.  From __send_signal()'s pov they mean

	SEND_SIG_NOINFO		from user
	SEND_SIG_PRIV		from kernel
	SEND_SIG_FORCED		no info

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Reviewed-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 13 insertions, 8 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f4c145410a8d..57b3516f055b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2102,11 +2102,6 @@ static inline int kill_cad_pid(int sig, int priv)
 #define SEND_SIG_PRIV   ((struct siginfo *) 1)
 #define SEND_SIG_FORCED ((struct siginfo *) 2)
 
-static inline int is_si_special(const struct siginfo *info)
-{
-        return info <= SEND_SIG_FORCED;
-}
-
 /*
  * True if we are on the alternate signal stack.
  */
diff --git a/kernel/signal.c b/kernel/signal.c
index 6b982f2cf524..a0ba428954b6 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -607,6 +607,17 @@ static int rm_from_queue(unsigned long mask, struct sigpending *s)
         return 1;
 }
 
+static inline int is_si_special(const struct siginfo *info)
+{
+        return info <= SEND_SIG_FORCED;
+}
+
+static inline bool si_fromuser(const struct siginfo *info)
+{
+        return info == SEND_SIG_NOINFO ||
+                (!is_si_special(info) && SI_FROMUSER(info));
+}
+
 /*
  * Bad permissions for sending the signal
  * - the caller must hold at least the RCU read lock
@@ -621,7 +632,7 @@ static int check_kill_permission(int sig, struct siginfo *info,
         if (!valid_signal(sig))
                 return -EINVAL;
 
-        if (info != SEND_SIG_NOINFO && (is_si_special(info) || SI_FROMKERNEL(info)))
+        if (!si_fromuser(info))
                 return 0;
 
         error = audit_signal_info(sig, t); /* Let audit system see the signal */
@@ -1186,8 +1197,7 @@ int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
                 goto out_unlock;
         }
         pcred = __task_cred(p);
-        if ((info == SEND_SIG_NOINFO ||
-             (!is_si_special(info) && SI_FROMUSER(info))) &&
+        if (si_fromuser(info) &&
             euid != pcred->suid && euid != pcred->uid &&
             uid  != pcred->suid && uid  != pcred->uid) {
                 ret = -EPERM;