[PATCH v3] mm: memdup_user*() should use same gfp flags

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

syzbot is reporting that memdup_user_nul() which receives user-controlled
size (which can be up to (INT_MAX & PAGE_MASK)) via vfs_write() will hit
order >= MAX_ORDER path [1].

Making costly allocations (order > PAGE_ALLOC_COSTLY_ORDER) naturally fail
should be better than trying to enforce PAGE_SIZE upper limit, for some of
callers accept space-delimited list arguments.

Therefore, let's add __GFP_NOWARN to memdup_user_nul() as with
commit 6c8fcc096be9d02f ("mm: don't let userspace spam allocations
warnings"). Also use GFP_USER as with other userspace-controllable
allocations like memdup_user().

[1] https://syzkaller.appspot.com/bug?id=8bf7efb3db19101b4008dc9198522ef977d098a6

Reported-by: syzbot <syzbot+a71a442385a0b2815497@syzkaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 mm/util.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 8c9b7d1e7c49..265b40a86856 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -252,12 +252,7 @@ void *memdup_user_nul(const void __user *src, size_t len)
 {
 	char *p;
 
-	/*
-	 * Always use GFP_KERNEL, since copy_from_user() can sleep and
-	 * cause pagefault, which makes it pointless to use GFP_NOFS
-	 * or GFP_ATOMIC.
-	 */
-	p = kmalloc_track_caller(len + 1, GFP_KERNEL);
+	p = kmalloc_track_caller(len + 1, GFP_USER | __GFP_NOWARN);
 	if (!p)
 		return ERR_PTR(-ENOMEM);
 
-- 
2.18.4