[PATCH] compat: Fix endian issue in union sigval

On Wed, Feb 11, 2015 at 07:22:08PM +0800, Bamvor Jian Zhang wrote:

On 2015/2/10 20:27, Catalin Marinas wrote:

quoted

On Tue, Feb 10, 2015 at 10:10:11AM +0000, Zhang Jian(Bamvor) wrote:

quoted

In 64bit architecture, sigval_int is the high 32bit of sigval_ptr in
big endian kernel compare with low 32bit of sigval_ptr in little
endian kernel. reference:

    typedef union sigval {
        int sival_int;
        void *sival_ptr;
    } sigval_t;

During compat_mq_notify or compat_timer_create, kernel get sigval
from user space by reading sigval.sival_int. This is correct in 32 bit
kernel and in 64bit little endian kernel. And It is wrong in 64bit big
endian kernel:
It get the high 32bit of sigval_ptr and put it to low 32bit of
sigval_ptr. And the high 32bit sigval_ptr in empty in arm 32bit user
space struct. So, kernel lost the value of sigval_ptr.

The following patch get the sigval_ptr in stead of sigval_int in order
to avoid endian issue.
Test pass in arm64 big endian and little endian kernel.

Signed-off-by: Zhang Jian(Bamvor) <redacted>
---
 ipc/compat_mq.c | 7 ++-----
 kernel/compat.c | 6 ++----
 2 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/ipc/compat_mq.c b/ipc/compat_mq.c
index ef6f91c..2e07343 100644
--- a/ipc/compat_mq.c
+++ b/ipc/compat_mq.c

@@ -99,11 +99,8 @@ COMPAT_SYSCALL_DEFINE2(mq_notify, mqd_t, mqdes,
 	if (u_notification) {
 		struct sigevent n;
 		p = compat_alloc_user_space(sizeof(*p));
-		if (get_compat_sigevent(&n, u_notification))
-			return -EFAULT;
-		if (n.sigev_notify == SIGEV_THREAD)
-			n.sigev_value.sival_ptr = compat_ptr(n.sigev_value.sival_int);
-		if (copy_to_user(p, &n, sizeof(*p)))
+		if (get_compat_sigevent(&n, u_notification) ||
+		    copy_to_user(p, &n, sizeof(*p)))
 			return -EFAULT;

The kernel doesn't need to interpret the sival_ptr value, it's something
to be passed to the notifier function as an argument.

Actually I was wrong here. The kernel _does_ interpret the sival_ptr to
read a cookie in sys_mq_notify() for PF_NETLINK sockets. So this code is
correct.

quoted

quoted

 	}
 	return sys_mq_notify(mqdes, p);

diff --git a/kernel/compat.c b/kernel/compat.c
index ebb3c36..13a0e5d 100644
--- a/kernel/compat.c
+++ b/kernel/compat.c

@@ -871,16 +871,14 @@ COMPAT_SYSCALL_DEFINE4(clock_nanosleep, clockid_t, which_clock, int, flags,
  * We currently only need the following fields from the sigevent
  * structure: sigev_value, sigev_signo, sig_notify and (sometimes
  * sigev_notify_thread_id).  The others are handled in user mode.
- * We also assume that copying sigev_value.sival_int is sufficient
- * to keep all the bits of sigev_value.sival_ptr intact.
  */
 int get_compat_sigevent(struct sigevent *event,
 		const struct compat_sigevent __user *u_event)
 {
 	memset(event, 0, sizeof(*event));
 	return (!access_ok(VERIFY_READ, u_event, sizeof(*u_event)) ||
-		__get_user(event->sigev_value.sival_int,
-			&u_event->sigev_value.sival_int) ||
+		__get_user(*(long long*)event->sigev_value.sival_ptr,

should be:
		__get_user(event->sigev_value.sival_ptr,

quoted

quoted

+         &u_event->sigev_value.sival_ptr) ||

I don't think this is correct because some (most) architectures use
sival_int here when copying to user and for a big endian compat they
would get 0 for sival_int (mips, powerpc).

Sorry, I am lost here. As we mentioned above, sival_ptr and sival_int
is union, so, copy sival_ptr should include sival_int.

The user access size in your patch is the size of sival_ptr which is
32-bit for compat, same as sival_int; so far, so good. However, when you
store it to the native sival_ptr, you perform a conversion to long long
(shouldn't it be unsigned long long, or just unsigned long?).

The native sigval_t is also a union but on 64-bit big endian, the
sival_int overlaps with the most significant 32-bit of the sival_ptr.
So reading sival_int would always be 0. When the compat siginfo is
copied to user, arm64 reads the native sival_ptr (si_ptr) and converts
it to the compat one, getting the correct 32-bit value. However, other
architectures access sival_int (si_int) instead which breaks with your
get_compat_sigevent() changes.

quoted

I think the correct fix is in the arm64 code:

The following code could fix my issue.

Without any parts of your patch?

I think that's correct fix since in the SIGEV_THREAD mq_notify case, we
would not deliver a signal as notification, so the sival_int value is
irrelevant (it would be 0 for big-endian compat tasks because of the
sigval_t union on 64-bit).

Your patch would work as well but you have to change all the other
architectures to use si_ptr when copying to a compat siginfo.

quoted

diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index e299de396e9b..32601939a3c8 100644
--- a/arch/arm64/kernel/signal32.c
+++ b/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;
 	case __SI_SYS:
 		err |= __put_user((compat_uptr_t)(unsigned long)

-- 
Catalin