Patch "tun: fix tun_napi_alloc_frags() frag allocator" has been added to the 4.15-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    tun: fix tun_napi_alloc_frags() frag allocator

to the 4.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tun-fix-tun_napi_alloc_frags-frag-allocator.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 43a08e0f58b3f236165029710a4e3b303815253b Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Thu, 15 Feb 2018 14:47:15 -0800
Subject: tun: fix tun_napi_alloc_frags() frag allocator
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Eric Dumazet <edumazet@google.com>

commit 43a08e0f58b3f236165029710a4e3b303815253b upstream.

<Mark Rutland reported>
    While fuzzing arm64 v4.16-rc1 with Syzkaller, I've been hitting a
    misaligned atomic in __skb_clone:

        atomic_inc(&(skb_shinfo(skb)->dataref));

   where dataref doesn't have the required natural alignment, and the
   atomic operation faults. e.g. i often see it aligned to a single
   byte boundary rather than a four byte boundary.

   AFAICT, the skb_shared_info is misaligned at the instant it's
   allocated in __napi_alloc_skb()  __napi_alloc_skb()
</end of report>

Problem is caused by tun_napi_alloc_frags() using
napi_alloc_frag() with user provided seg sizes,
leading to other users of this API getting unaligned
page fragments.

Since we would like to not necessarily add paddings or alignments to
the frags that tun_napi_alloc_frags() attaches to the skb, switch to
another page frag allocator.

As a bonus skb_page_frag_refill() can use GFP_KERNEL allocations,
meaning that we can not deplete memory reserves as easily.

Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/net/tun.c |   16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1317,27 +1317,23 @@ static struct sk_buff *tun_napi_alloc_fr
 	skb->truesize += skb->data_len;
 
 	for (i = 1; i < it->nr_segs; i++) {
+		struct page_frag *pfrag = &current->task_frag;
 		size_t fragsz = it->iov[i].iov_len;
-		unsigned long offset;
-		struct page *page;
-		void *data;
 
 		if (fragsz == 0 || fragsz > PAGE_SIZE) {
 			err = -EINVAL;
 			goto free;
 		}
 
-		local_bh_disable();
-		data = napi_alloc_frag(fragsz);
-		local_bh_enable();
-		if (!data) {
+		if (!skb_page_frag_refill(fragsz, pfrag, GFP_KERNEL)) {
 			err = -ENOMEM;
 			goto free;
 		}
 
-		page = virt_to_head_page(data);
-		offset = data - page_address(page);
-		skb_fill_page_desc(skb, i - 1, page, offset, fragsz);
+		skb_fill_page_desc(skb, i - 1, pfrag->page,
+				   pfrag->offset, fragsz);
+		page_ref_inc(pfrag->page);
+		pfrag->offset += fragsz;
 	}
 
 	return skb;


Patches currently in stable-queue which might be from edumazet@google.com are

queue-4.15/net_sched-gen_estimator-fix-lockdep-splat.patch
queue-4.15/tun-fix-tun_napi_alloc_frags-frag-allocator.patch
queue-4.15/netfilter-x_tables-avoid-out-of-bounds-reads-in-xt_request_find_-match-target.patch
queue-4.15/netfilter-xt_rateest-acquire-xt_rateest_mutex-for-hash-insert.patch