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mm/migrate: fix do_pages_move for compat pointers

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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 5b1b561ba7 ("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/20231003144857.752952-1-gregory.price@memverge.com
Fixes: 5b1b561ba7 ("mm: simplify compat_sys_move_pages")
Signed-off-by: Gregory Price <gregory.price@memverge.com>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Co-developed-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Gregory Price 2023-10-03 10:48:56 -04:00 committed by Andrew Morton
parent 1de195dd0e
commit 229e225376
1 changed files with 12 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

10
mm/migrate.c
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@ -2162,6 +2162,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
const int __user *nodes, const int __user *nodes,
int __user *status, int flags) int __user *status, int flags)
{ {
compat_uptr_t __user *compat_pages = (void __user *)pages;
int current_node = NUMA_NO_NODE; int current_node = NUMA_NO_NODE;
LIST_HEAD(pagelist); LIST_HEAD(pagelist);
int start, i; int start, i;
@ -2174,8 +2175,17 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
int node; int node;
err = -EFAULT; err = -EFAULT;
if (in_compat_syscall()) {
compat_uptr_t cp;
if (get_user(cp, compat_pages + i))
goto out_flush;
p = compat_ptr(cp);
} else {
if (get_user(p, pages + i)) if (get_user(p, pages + i))
goto out_flush; goto out_flush;
}
if (get_user(node, nodes + i)) if (get_user(node, nodes + i))
goto out_flush; goto out_flush;