y2038: socket: Add compat_sys_recvmmsg_time64

recvmmsg() takes two arguments to pointers of structures that differ
between 32-bit and 64-bit architectures: mmsghdr and timespec.

For y2038 compatbility, we are changing the native system call from
timespec to __kernel_timespec with a 64-bit time_t (in another patch),
and use the existing compat system call on both 32-bit and 64-bit
architectures for compatibility with traditional 32-bit user space.

As we now have two variants of recvmmsg() for 32-bit tasks that are both
different from the variant that we use on 64-bit tasks, this means we
also require two compat system calls!

The solution I picked is to flip things around: The existing
compat_sys_recvmmsg() call gets moved from net/compat.c into net/socket.c
and now handles the case for old user space on all architectures that
have set CONFIG_COMPAT_32BIT_TIME.  A new compat_sys_recvmmsg_time64()
call gets added in the old place for 64-bit architectures only, this
one handles the case of a compat mmsghdr structure combined with
__kernel_timespec.

In the indirect sys_socketcall(), we now need to call either
do_sys_recvmmsg() or __compat_sys_recvmmsg(), depending on what kind of
architecture we are on. For compat_sys_socketcall(), no such change is
needed, we always call __compat_sys_recvmmsg().

I decided to not add a new SYS_RECVMMSG_TIME64 socketcall: Any libc
implementation for 64-bit time_t will need significant changes including
an updated asm/unistd.h, and it seems better to consistently use the
separate syscalls that configuration, leaving the socketcall only for
backward compatibility with 32-bit time_t based libc.

The naming is asymmetric for the moment, so both existing syscalls
entry points keep their names, while the new ones are recvmmsg_time32
and compat_recvmmsg_time64 respectively. I expect that we will rename
the compat syscalls later as we start using generated syscall tables
everywhere and add these entry points.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 12 insertions, 22 deletions

diff --git a/net/compat.c b/net/compat.c
index 47a614b370cd..f7084780a8f8 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -810,34 +810,23 @@ COMPAT_SYSCALL_DEFINE6(recvfrom, int, fd, void __user *, buf, compat_size_t, len
         return __compat_sys_recvfrom(fd, buf, len, flags, addr, addrlen);
 }
 
-static int __compat_sys_recvmmsg(int fd, struct compat_mmsghdr __user *mmsg,
-                                 unsigned int vlen, unsigned int flags,
-                                 struct old_timespec32 __user *timeout)
+COMPAT_SYSCALL_DEFINE5(recvmmsg_time64, int, fd, struct compat_mmsghdr __user *, mmsg,
+                       unsigned int, vlen, unsigned int, flags,
+                       struct __kernel_timespec __user *, timeout)
 {
-        int datagrams;
-        struct timespec64 ktspec;
-
-        if (timeout == NULL)
-                return __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
-                                      flags | MSG_CMSG_COMPAT, NULL);
-
-        if (compat_get_timespec64(&ktspec, timeout))
-                return -EFAULT;
-
-        datagrams = __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
-                                   flags | MSG_CMSG_COMPAT, &ktspec);
-        if (datagrams > 0 && compat_put_timespec64(&ktspec, timeout))
-                datagrams = -EFAULT;
-
-        return datagrams;
+        return __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
+                              flags | MSG_CMSG_COMPAT, timeout, NULL);
 }
 
+#ifdef CONFIG_COMPAT_32BIT_TIME
 COMPAT_SYSCALL_DEFINE5(recvmmsg, int, fd, struct compat_mmsghdr __user *, mmsg,
                        unsigned int, vlen, unsigned int, flags,
                        struct old_timespec32 __user *, timeout)
 {
-        return __compat_sys_recvmmsg(fd, mmsg, vlen, flags, timeout);
+        return __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
+                              flags | MSG_CMSG_COMPAT, NULL, timeout);
 }
+#endif
 
 COMPAT_SYSCALL_DEFINE2(socketcall, int, call, u32 __user *, args)
 {
@@ -925,8 +914,9 @@ COMPAT_SYSCALL_DEFINE2(socketcall, int, call, u32 __user *, args)
                 ret = __compat_sys_recvmsg(a0, compat_ptr(a1), a[2]);
                 break;
         case SYS_RECVMMSG:
-                ret = __compat_sys_recvmmsg(a0, compat_ptr(a1), a[2], a[3],
-                                            compat_ptr(a[4]));
+                ret = __sys_recvmmsg(a0, compat_ptr(a1), a[2],
+                                     a[3] | MSG_CMSG_COMPAT, NULL,
+                                     compat_ptr(a[4]));
                 break;
         case SYS_ACCEPT4:
                 ret = __sys_accept4(a0, compat_ptr(a1), compat_ptr(a[2]), a[3]);