On Tue, Oct 27, 2020 at 11:25 AM Tung Nguyen
<tung.q.ngu...@dektech.com.au> wrote:
>
> Commit ed42989eab57 ("tipc: fix the skb_unshare() in tipc_buf_append()")
> replaced skb_unshare() with skb_copy() to not reduce the data reference
> counter of the original skb intentionally. This is not the correct
> way to handle the cloned skb because it causes memory leak in 2
> following cases:
> 1/ Sending multicast messages via broadcast link
> The original skb list is cloned to the local skb list for local
> destination. After that, the data reference counter of each skb
> in the original list has the value of 2. This causes each skb not
> to be freed after receiving ACK:
> tipc_link_advance_transmq()
> {
> ...
> /* release skb */
> __skb_unlink(skb, &l->transmq);
> kfree_skb(skb); <-- memory exists after being freed
> }
>
> 2/ Sending multicast messages via replicast link
> Similar to the above case, each skb cannot be freed after purging
> the skb list:
> tipc_mcast_xmit()
> {
> ...
> __skb_queue_purge(pkts); <-- memory exists after being freed
> }
>
> This commit fixes this issue by using skb_unshare() instead. Besides,
> to avoid use-after-free error reported by KASAN, the pointer to the
> fragment is set to NULL before calling skb_unshare() to make sure that
> the original skb is not freed after freeing the fragment 2 times in
> case skb_unshare() returns NULL.
>
> Fixes: ed42989eab57 ("tipc: fix the skb_unshare() in tipc_buf_append()")
> Acked-by: Jon Maloy <jma...@redhat.com>
> Reported-by: Thang Hoang Ngo <thang.h....@dektech.com.au>
> Signed-off-by: Tung Nguyen <tung.q.ngu...@dektech.com.au>
Reviewed-by: Xin Long <lucien....@gmail.com>
> ---
> net/tipc/msg.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/net/tipc/msg.c b/net/tipc/msg.c
> index 2a78aa701572..32c79c59052b 100644
> --- a/net/tipc/msg.c
> +++ b/net/tipc/msg.c
> @@ -150,12 +150,11 @@ int tipc_buf_append(struct sk_buff **headbuf, struct
> sk_buff **buf)
> if (fragid == FIRST_FRAGMENT) {
> if (unlikely(head))
> goto err;
> - if (skb_cloned(frag))
> - frag = skb_copy(frag, GFP_ATOMIC);
> + *buf = NULL;
> + frag = skb_unshare(frag, GFP_ATOMIC);
> if (unlikely(!frag))
> goto err;
> head = *headbuf = frag;
> - *buf = NULL;
> TIPC_SKB_CB(head)->tail = NULL;
> if (skb_is_nonlinear(head)) {
> skb_walk_frags(head, tail) {
> --
> 2.17.1
>
>
>
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