Re: [PATCH] net/rxrpc: Fix a use after free in rxrpc_input_packet
Lv Yunlong 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(_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
[PATCH] net/rxrpc: Fix a use after free in rxrpc_input_packet
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,..).
I see that rxrpc_eaten_skb() is used to drop a ref of skb. As the skb
is already freed in skb_unshare() on error, my patch removes the
rxrpc_eaten_skb() to avoid the uaf.
Fixes: d0d5c0cd1e711 ("rxrpc: Use skb_unshare() rather than skb_cow_data()")
Signed-off-by: Lv Yunlong
---
net/rxrpc/input.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index dc201363f2c4..9ba408064465 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -1281,10 +1281,8 @@ int rxrpc_input_packet(struct sock *udp_sk, struct
sk_buff *skb)
*/
if (sp->hdr.securityIndex != 0) {
struct sk_buff *nskb = skb_unshare(skb, GFP_ATOMIC);
- if (!nskb) {
- rxrpc_eaten_skb(skb, rxrpc_skb_unshared_nomem);
+ if (!nskb)
goto out;
- }
if (nskb != skb) {
rxrpc_eaten_skb(skb, rxrpc_skb_received);
--
2.25.1
