From 43a08e0f58b3f236165029710a4e3b303815253b Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 15 Feb 2018 14:47:15 -0800 Subject: [PATCH] tun: fix tun_napi_alloc_frags() frag allocator MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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() 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 Reported-by: Mark Rutland Tested-by: Mark Rutland Signed-off-by: David S. Miller --- drivers/net/tun.c | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 81e6cc951e7f..b52258c327d2 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1489,27 +1489,23 @@ static struct sk_buff *tun_napi_alloc_frags(struct tun_file *tfile, skb->truesize += skb->data_len; for (i = 1; i < it->nr_segs; i++) { + struct page_frag *pfrag = ¤t->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; -- 2.30.2