[PATCH] compat: Fix endian issue in union sigval

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

cc'ing linux-arch as well.

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.

Yeah, this is the reason why I try to fix sival_ptr through
get_compat_sigevent before sys_mq_notify. After this compat wrapper,
sys_mq_notify will put the sival_ptr to nc buffer(file ipc/mqueue.c line 1221
to line 1226):
    if (copy_from_user(nc->data,
                    notification.sigev_value.sival_ptr,
                    NOTIFY_COOKIE_LEN)) {
            ret = -EFAULT;
            goto out;
    }
    /* TODO: add a header? */
    skb_put(nc, NOTIFY_COOKIE_LEN);
    /* and attach it to the socket */

The original changes is introduced by Alexander Viro
[off-list ref] more than ten years ago[1]:

author   Alexander Viro [off-list ref] 2004-07-13 04:02:57 (GMT)
committer   Linus Torvalds [off-list ref]   2004-07-13 04:02:57 (GMT)
commit  95b5842264ac470a1a3a59d2741bb18adb140c8b (patch)
tree    5167f68fae8f3bbc9b3a2d7617d1500356837c16 /ipc/compat_mq.c
parent  de54add33621c5b4a1be895c82b7af96fb4dd447 (diff)
[PATCH] sparse: ipc compat annotations and cleanups
    ipc compat code switched to compat_alloc_user_space() and annotated.

For the user's
convenience, it is a union of an int and ptr. So I think the original
SIGEV_THREAD check and compat_ptr() conversion here is wrong, it
shouldn't exist at all (it doesn't exist in compat_sys_timer_create
either). This hunk looks fine to me.

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

+         &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.

I think the correct fix is in the arm64 code:

The following code could fix my issue.

regards

bamvor