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Date: Thu, 8 Oct 2020 16:45:05 +0800 From: Xin Long <lucien.xin@...il.com> To: Cong Wang <xiyou.wangcong@...il.com> Cc: network dev <netdev@...r.kernel.org>, syzbot <syzbot+e96a7ba46281824cc46a@...kaller.appspotmail.com>, Jon Maloy <jmaloy@...hat.com>, Ying Xue <ying.xue@...driver.com> Subject: Re: [Patch net] tipc: fix the skb_unshare() in tipc_buf_append() On Thu, Oct 8, 2020 at 12:12 PM Cong Wang <xiyou.wangcong@...il.com> wrote: > > skb_unshare() drops a reference count on the old skb unconditionally, > so in the failure case, we end up freeing the skb twice here. > And because the skb is allocated in fclone and cloned by caller > tipc_msg_reassemble(), the consequence is actually freeing the > original skb too, thus triggered the UAF by syzbot. Do you mean: frag = skb_clone(skb, GFP_ATOMIC); frag = skb_unshare(frag) will free the 'skb' too? > > Fix this by replacing this skb_unshare() with skb_cloned()+skb_copy(). > > Fixes: ff48b6222e65 ("tipc: use skb_unshare() instead in tipc_buf_append()") > Reported-and-tested-by: syzbot+e96a7ba46281824cc46a@...kaller.appspotmail.com > Cc: Xin Long <lucien.xin@...il.com> > Cc: Jon Maloy <jmaloy@...hat.com> > Cc: Ying Xue <ying.xue@...driver.com> > Signed-off-by: Cong Wang <xiyou.wangcong@...il.com> > --- > net/tipc/msg.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/net/tipc/msg.c b/net/tipc/msg.c > index 52e93ba4d8e2..681224401871 100644 > --- a/net/tipc/msg.c > +++ b/net/tipc/msg.c > @@ -150,7 +150,8 @@ int tipc_buf_append(struct sk_buff **headbuf, struct sk_buff **buf) > if (fragid == FIRST_FRAGMENT) { > if (unlikely(head)) > goto err; > - frag = skb_unshare(frag, GFP_ATOMIC); > + if (skb_cloned(frag)) > + frag = skb_copy(frag, GFP_ATOMIC); > if (unlikely(!frag)) > goto err; > head = *headbuf = frag; > -- > 2.28.0 >
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