mm/migrate: fix do_pages_move for compat pointers

do_pages_move does not handle compat pointers for the page list. 
correctly.  Add in_compat_syscall check and appropriate get_user fetch
when iterating the page list.

It makes the syscall in compat mode (32-bit userspace, 64-bit kernel)
work the same way as the native 32-bit syscall again, restoring the
behavior before my broken commit 5b1b561ba73c ("mm: simplify
compat_sys_move_pages").

More specifically, my patch moved the parsing of the 'pages' array from
the main entry point into do_pages_stat(), which left the syscall
working correctly for the 'stat' operation (nodes = NULL), while the
'move' operation (nodes != NULL) is now missing the conversion and
interprets 'pages' as an array of 64-bit pointers instead of the
intended 32-bit userspace pointers.

It is possible that nobody noticed this bug because the few
applications that actually call move_pages are unlikely to run in
compat mode because of their large memory requirements, but this
clearly fixes a user-visible regression and should have been caught by
ltp.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 5b1b561ba73c ("mm: simplify compat_sys_move_pages")
Signed-off-by: Gregory Price <[email protected]>
Reported-by: Arnd Bergmann <[email protected]>
Co-developed-by: Arnd Bergmann <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions