rxrpc: Fix use-after-free in rxrpc_receive_data()

The subpacket scanning loop in rxrpc_receive_data() references the
subpacket count in the private data part of the sk_buff in the loop
termination condition.  However, when the final subpacket is pasted into
the ring buffer, the function is no longer has a ref on the sk_buff and
should not be looking at sp->* any more.  This point is actually marked in
the code when skb is cleared (but sp is not - which is an error).

Fix this by caching sp->nr_subpackets in a local variable and using that
instead.

Also clear 'sp' to catch accesses after that point.

This can show up as an oops in rxrpc_get_skb() if sp->nr_subpackets gets
trashed by the sk_buff getting freed and reused in the meantime.

Fixes: e2de6c404898 ("rxrpc: Use info in skbuff instead of reparsing a jumbo packet")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index 86bd133..96d54e5 100644 (file)
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -413,7 +413,7 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
 {
        struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
        enum rxrpc_call_state state;
-       unsigned int j;
+       unsigned int j, nr_subpackets;
        rxrpc_serial_t serial = sp->hdr.serial, ack_serial = 0;
        rxrpc_seq_t seq0 = sp->hdr.seq, hard_ack;
        bool immediate_ack = false, jumbo_bad = false;
@@ -457,7 +457,8 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
        call->ackr_prev_seq = seq0;
        hard_ack = READ_ONCE(call->rx_hard_ack);
 
-       if (sp->nr_subpackets > 1) {
+       nr_subpackets = sp->nr_subpackets;
+       if (nr_subpackets > 1) {
                if (call->nr_jumbo_bad > 3) {
                        ack = RXRPC_ACK_NOSPACE;
                        ack_serial = serial;
@@ -465,11 +466,11 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
                }
        }
 
-       for (j = 0; j < sp->nr_subpackets; j++) {
+       for (j = 0; j < nr_subpackets; j++) {
                rxrpc_serial_t serial = sp->hdr.serial + j;
                rxrpc_seq_t seq = seq0 + j;
                unsigned int ix = seq & RXRPC_RXTX_BUFF_MASK;
-               bool terminal = (j == sp->nr_subpackets - 1);
+               bool terminal = (j == nr_subpackets - 1);
                bool last = terminal && (sp->rx_flags & RXRPC_SKB_INCL_LAST);
                u8 flags, annotation = j;
 
@@ -506,7 +507,7 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
                }
 
                if (call->rxtx_buffer[ix]) {
-                       rxrpc_input_dup_data(call, seq, sp->nr_subpackets > 1,
+                       rxrpc_input_dup_data(call, seq, nr_subpackets > 1,
                                             &jumbo_bad);
                        if (ack != RXRPC_ACK_DUPLICATE) {
                                ack = RXRPC_ACK_DUPLICATE;
@@ -564,6 +565,7 @@ static void rxrpc_input_data(struct rxrpc_call *call, struct sk_buff *skb)
                         * ring.
                         */
                        skb = NULL;
+                       sp = NULL;
                }
 
                if (last) {