[v3,2/4] mm: simplify compat_sys_move_pages

Commit Message

Arnd Bergmann May 17, 2021, 8:33 p.m. UTC

From: Arnd Bergmann <[e-mail]>

The compat move_pages() implementation uses compat_alloc_user_space()
for converting the pointer array. Moving the compat handling into
the function itself is a bit simpler and lets us avoid the
compat_alloc_user_space() call.

Signed-off-by: Arnd Bergmann <[e-mail]>
---
 mm/migrate.c | 45 ++++++++++++++++++++++++++++++---------------
 1 file changed, 30 insertions(+), 15 deletions(-)

Comments

Christoph Hellwig May 18, 2021, 6:42 a.m. UTC | #1

Looks good,

Reviewed-by: Christoph Hellwig <[e-mail]>

David Laight May 18, 2021, 8:49 p.m. UTC | #2

From: Arnd Bergmann
> Sent: 17 May 2021 21:34
> 
> The compat move_pages() implementation uses compat_alloc_user_space()
> for converting the pointer array. Moving the compat handling into
> the function itself is a bit simpler and lets us avoid the
> compat_alloc_user_space() call.
> 
> Signed-off-by: Arnd Bergmann <[e-mail]>
> ---
>  mm/migrate.c | 45 ++++++++++++++++++++++++++++++---------------
>  1 file changed, 30 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index b234c3f3acb7..a68d07f19a1a 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1855,6 +1855,23 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
>  	mmap_read_unlock(mm);
>  }
> 
> +static int put_compat_pages_array(const void __user *chunk_pages[],
> +				  const void __user * __user *pages,
> +				  unsigned long chunk_nr)
> +{

Should that be get_compat_pages_array() ?

	David

-
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Arnd Bergmann May 19, 2021, 1:41 p.m. UTC | #3

On Tue, May 18, 2021 at 10:49 PM David Laight <[e-mail]> wrote:
> >
> > +static int put_compat_pages_array(const void __user *chunk_pages[],
> > +                               const void __user * __user *pages,
> > +                               unsigned long chunk_nr)
> > +{
>
> Should that be get_compat_pages_array() ?

Nice catch, thanks!

Fixed now.

       Arnd

Patch

diff --git a/mm/migrate.c b/mm/migrate.c
index b234c3f3acb7..a68d07f19a1a 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1855,6 +1855,23 @@  static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
 	mmap_read_unlock(mm);
 }
 
+static int put_compat_pages_array(const void __user *chunk_pages[],
+				  const void __user * __user *pages,
+				  unsigned long chunk_nr)
+{
+	compat_uptr_t __user *pages32 = (compat_uptr_t __user *)pages;
+	compat_uptr_t p;
+	int i;
+
+	for (i = 0; i < chunk_nr; i++) {
+		if (get_user(p, pages32 + i))
+			return -EFAULT;
+		chunk_pages[i] = compat_ptr(p);
+	}
+
+	return 0;
+}
+
 /*
  * Determine the nodes of a user array of pages and store it in
  * a user array of status.
@@ -1874,8 +1891,15 @@  static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
 		if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
 			chunk_nr = DO_PAGES_STAT_CHUNK_NR;
 
-		if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
-			break;
+		if (in_compat_syscall()) {
+			if (put_compat_pages_array(chunk_pages, pages,
+						   chunk_nr))
+				break;
+		} else {
+			if (copy_from_user(chunk_pages, pages,
+				      chunk_nr * sizeof(*chunk_pages)))
+				break;
+		}
 
 		do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
 
@@ -1980,23 +2004,14 @@  SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
 
 #ifdef CONFIG_COMPAT
 COMPAT_SYSCALL_DEFINE6(move_pages, pid_t, pid, compat_ulong_t, nr_pages,
-		       compat_uptr_t __user *, pages32,
+		       compat_uptr_t __user *, pages,
 		       const int __user *, nodes,
 		       int __user *, status,
 		       int, flags)
 {
-	const void __user * __user *pages;
-	int i;
-
-	pages = compat_alloc_user_space(nr_pages * sizeof(void *));
-	for (i = 0; i < nr_pages; i++) {
-		compat_uptr_t p;
-
-		if (get_user(p, pages32 + i) ||
-			put_user(compat_ptr(p), pages + i))
-			return -EFAULT;
-	}
-	return kernel_move_pages(pid, nr_pages, pages, nodes, status, flags);
+	return kernel_move_pages(pid, nr_pages,
+				 (const void __user *__user *)pages,
+				 nodes, status, flags);
 }
 #endif /* CONFIG_COMPAT */