[PATCH 5.4 043/110] rxrpc: Fix use-after-free in rxrpc_receive_data()

Greg Kroah-Hartman
2020-01-30T18:43:44Z

From: David Howells <dhowells@redhat.com>

[ Upstream commit 122d74fac84204b9a98263636f6f9a3b2e665639 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/rxrpc/input.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -413,7 +413,7 @@ static void rxrpc_input_data(struct rxrp
{
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 rxrp
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 rxrp
}
}

- 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 rxrp
}

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 rxrp
* ring.
*/
skb = NULL;
+ sp = NULL;
}

if (last) {