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tun: fix tun_napi_alloc_frags() frag allocator 

<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: 90e33d4594 ("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>
This commit is contained in:
Eric Dumazet 2018-02-15 14:47:15 -08:00 committed by David S. Miller
parent 15f35d49c9
commit 43a08e0f58
1 changed files with 6 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
drivers/net/tun.c
View File

@ -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 = &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;