arm64: compat Fix siginfo_t -> compat_siginfo_t conversion on big endian

commit 9d42d48a upstream.

The native (64-bit) sigval_t union contains sival_int (32-bit) and
sival_ptr (64-bit). When a compat application invokes a syscall that
takes a sigval_t value (as part of a larger structure, e.g.
compat_sys_mq_notify, compat_sys_timer_create), the compat_sigval_t
union is converted to the native sigval_t with sival_int overlapping
with either the least or the most significant half of sival_ptr,
depending on endianness. When the corresponding signal is delivered to a
compat application, on big endian the current (compat_uptr_t)sival_ptr
cast always returns 0 since sival_int corresponds to the top part of
sival_ptr. This patch fixes copy_siginfo_to_user32() so that sival_int
is copied to the compat_siginfo_t structure.
Reported-by: Bamvor Jian Zhang <bamvor.zhangjian@huawei.com>
Tested-by: Bamvor Jian Zhang <bamvor.zhangjian@huawei.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

arch/arm64/kernel/signal32.c

@@ -154,8 +154,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
 	case __SI_TIMER:
 		 err |= __put_user(from->si_tid, &to->si_tid);
 		 err |= __put_user(from->si_overrun, &to->si_overrun);
-		 err |= __put_user((compat_uptr_t)(unsigned long)from->si_ptr,
-				   &to->si_ptr);
+		 err |= __put_user(from->si_int, &to->si_int);
 		break;
 	case __SI_POLL:
 		err |= __put_user(from->si_band, &to->si_band);
@@ -184,7 +183,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
 	case __SI_MESGQ: /* But this is */
 		err |= __put_user(from->si_pid, &to->si_pid);
 		err |= __put_user(from->si_uid, &to->si_uid);
-		err |= __put_user((compat_uptr_t)(unsigned long)from->si_ptr, &to->si_ptr);
+		err |= __put_user(from->si_int, &to->si_int);
 		break;
 	default: /* this is just in case for now ... */
 		err |= __put_user(from->si_pid, &to->si_pid);