Lv Yunlong <lyl2...@mail.ustc.edu.cn> wrote:
> In the case RXRPC_PACKET_TYPE_DATA of rxrpc_input_packet, if
> skb_unshare(skb,..) failed, it will free the skb and return NULL.
> But if skb_unshare() return NULL, the freed skb will be used by
> rxrpc_eaten_skb(skb,..).
That's not precisely the case:
void rxrpc_eaten_skb(struct sk_buff *skb, enum rxrpc_skb_trace op)
{
const void *here = __builtin_return_address(0);
int n = atomic_inc_return(&rxrpc_n_rx_skbs);
trace_rxrpc_skb(skb, op, 0, n, 0, here);
}
The only thing that happens to skb here is that it's passed to
trace_rxrpc_skb(), but that doesn't dereference it either. The *address* is
used for display purposes, but that's all.
> I see that rxrpc_eaten_skb() is used to drop a ref of skb.
It isn't.
> As the skb is already freed in skb_unshare() on error, my patch removes the
> rxrpc_eaten_skb() to avoid the uaf.
But you remove the accounting, which might lead to an assertion failure in
af_rxrpc_exit().
That said, rxrpc_eaten_skb() should probably decrement rxrpc_n_rx_skbs, not
increment it...
David
