linux-kernel - Re: NULL-ptr deref in mmput via sys_migrate_pages in 3.4-rc4 (proly missing mm==NULL check)

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Date:	Wed, 25 Apr 2012 16:15:40 -0400
From:	Dave Jones <davej@...hat.com>
To:	Robert Święcki <robert@...ecki.net>
Cc:	linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux.com>,
	linux-mm@...ck.org
Subject: Re: NULL-ptr deref in mmput via sys_migrate_pages in 3.4-rc4 (proly
 missing mm==NULL check)

Commit 3268c63eded4612a3d07b56d1e02ce7731e6608e introduced two potential NULL dereferences.
Move the mmput calls into the if arms that have already tested for a valid mm.

Reported-by: Robert Święcki <robert@...ecki.net>
Cc: Christoph Lameter <cl@...ux.com>
Signed-off-by: Dave Jones <davej@...hat.com>

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index cfb6c86..6de4850 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1361,13 +1361,12 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
 
 	mm = get_task_mm(task);
 	put_task_struct(task);
-	if (mm)
+	if (mm) {
 		err = do_migrate_pages(mm, old, new,
 			capable(CAP_SYS_NICE) ? MPOL_MF_MOVE_ALL : MPOL_MF_MOVE);
-	else
+		mmput(mm);
+	} else
 		err = -EINVAL;
-
-	mmput(mm);
 out:
 	NODEMASK_SCRATCH_FREE(scratch);
 
diff --git a/mm/migrate.c b/mm/migrate.c
index 51c08a0..d73d860 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1389,15 +1389,15 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
 	put_task_struct(task);
 
 	if (mm) {
-		if (nodes)
+		if (nodes) {
 			err = do_pages_move(mm, task_nodes, nr_pages, pages,
 					    nodes, status, flags);
-		else
+			mmput(mm);
+		} else
 			err = do_pages_stat(mm, nr_pages, pages, status);
 	} else
 		err = -EINVAL;
 
-	mmput(mm);
 	return err;
 
 out:
--
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