s390/compat: correct uc_sigmask of the compat signal frame

The uc_sigmask in the ucontext structure is an array of words to keep
the 64 signal bits (or 1024 if you ask glibc but the kernel sigset_t
only has 64 bits).

For 64 bit the sigset_t contains a single 8 byte word, but for 31 bit
there are two 4 byte words. The compat signal handler code uses a
simple copy of the 64 bit sigset_t to the 31 bit compat_sigset_t.
As s390 is a big-endian architecture this is incorrect, the two words
in the 31 bit sigset_t array need to be swapped.

Cc: <stable@vger.kernel.org>
Reported-by: Stefan Liebler <stli@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/compat_signal.c

@@ -48,6 +48,19 @@ typedef struct
 	struct ucontext32 uc;
 } rt_sigframe32;
 
+static inline void sigset_to_sigset32(unsigned long *set64,
+				      compat_sigset_word *set32)
+{
+	set32[0] = (compat_sigset_word) set64[0];
+	set32[1] = (compat_sigset_word)(set64[0] >> 32);
+}
+
+static inline void sigset32_to_sigset(compat_sigset_word *set32,
+				      unsigned long *set64)
+{
+	set64[0] = (unsigned long) set32[0] | ((unsigned long) set32[1] << 32);
+}
+
 int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
 {
 	int err;
@@ -281,10 +294,12 @@ COMPAT_SYSCALL_DEFINE0(sigreturn)
 {
 	struct pt_regs *regs = task_pt_regs(current);
 	sigframe32 __user *frame = (sigframe32 __user *)regs->gprs[15];
+	compat_sigset_t cset;
 	sigset_t set;
 
-	if (__copy_from_user(&set.sig, &frame->sc.oldmask, _SIGMASK_COPY_SIZE32))
+	if (__copy_from_user(&cset.sig, &frame->sc.oldmask, _SIGMASK_COPY_SIZE32))
 		goto badframe;
+	sigset32_to_sigset(cset.sig, set.sig);
 	set_current_blocked(&set);
 	save_fpu_regs();
 	if (restore_sigregs32(regs, &frame->sregs))
@@ -302,10 +317,12 @@ COMPAT_SYSCALL_DEFINE0(rt_sigreturn)
 {
 	struct pt_regs *regs = task_pt_regs(current);
 	rt_sigframe32 __user *frame = (rt_sigframe32 __user *)regs->gprs[15];
+	compat_sigset_t cset;
 	sigset_t set;
 
-	if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
+	if (__copy_from_user(&cset, &frame->uc.uc_sigmask, sizeof(cset)))
 		goto badframe;
+	sigset32_to_sigset(cset.sig, set.sig);
 	set_current_blocked(&set);
 	if (compat_restore_altstack(&frame->uc.uc_stack))
 		goto badframe;
@@ -377,7 +394,7 @@ static int setup_frame32(struct ksignal *ksig, sigset_t *set,
 		return -EFAULT;
 
 	/* Create struct sigcontext32 on the signal stack */
-	memcpy(&sc.oldmask, &set->sig, _SIGMASK_COPY_SIZE32);
+	sigset_to_sigset32(set->sig, sc.oldmask);
 	sc.sregs = (__u32)(unsigned long __force) &frame->sregs;
 	if (__copy_to_user(&frame->sc, &sc, sizeof(frame->sc)))
 		return -EFAULT;
@@ -438,6 +455,7 @@ static int setup_frame32(struct ksignal *ksig, sigset_t *set,
 static int setup_rt_frame32(struct ksignal *ksig, sigset_t *set,
 			    struct pt_regs *regs)
 {
+	compat_sigset_t cset;
 	rt_sigframe32 __user *frame;
 	unsigned long restorer;
 	size_t frame_size;
@@ -485,11 +503,12 @@ static int setup_rt_frame32(struct ksignal *ksig, sigset_t *set,
 	store_sigregs();
 
 	/* Create ucontext on the signal stack. */
+	sigset_to_sigset32(set->sig, cset.sig);
 	if (__put_user(uc_flags, &frame->uc.uc_flags) ||
 	    __put_user(0, &frame->uc.uc_link) ||
 	    __compat_save_altstack(&frame->uc.uc_stack, regs->gprs[15]) ||
 	    save_sigregs32(regs, &frame->uc.uc_mcontext) ||
-	    __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set)) ||
+	    __copy_to_user(&frame->uc.uc_sigmask, &cset, sizeof(cset)) ||
 	    save_sigregs_ext32(regs, &frame->uc.uc_mcontext_ext))
 		return -EFAULT;