[PATCH AUTOSEL 4.19 580/671] llc: fix sk_buff refcounting in llc_conn_state_process()

Sasha Levin
2020-01-16T18:38:16Z

From: Eric Biggers <ebiggers@google.com>

[ Upstream commit 36453c852816f19947ca482a595dffdd2efa4965 ]

If llc_conn_state_process() sees that llc_conn_service() put the skb on
a list, it will drop one fewer references to it. This is wrong because
the current behavior is that llc_conn_service() never consumes a
reference to the skb.

The code also makes the number of skb references being dropped
conditional on which of ind_prim and cfm_prim are nonzero, yet neither
of these affects how many references are *acquired*. So there is extra
code that tries to fix this up by sometimes taking another reference.

Remove the unnecessary/broken refcounting logic and instead just add an
skb_get() before the only two places where an extra reference is
actually consumed.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/llc/llc_conn.c | 33 ++++++---------------------------
1 file changed, 6 insertions(+), 27 deletions(-)

diff --git a/net/llc/llc_conn.c b/net/llc/llc_conn.c
index 0b0c6f12153b..a79b739eb223 100644
--- a/net/llc/llc_conn.c
+++ b/net/llc/llc_conn.c
@@ -64,12 +64,6 @@ int llc_conn_state_process(struct sock *sk, struct sk_buff *skb)
struct llc_sock *llc = llc_sk(skb->sk);
struct llc_conn_state_ev *ev = llc_conn_ev(skb);

- /*
- * We have to hold the skb, because llc_conn_service will kfree it in
- * the sending path and we need to look at the skb->cb, where we encode
- * llc_conn_state_ev.
- */
- skb_get(skb);
ev->ind_prim = ev->cfm_prim = 0;
/*
* Send event to state machine
@@ -77,21 +71,12 @@ int llc_conn_state_process(struct sock *sk, struct sk_buff *skb)
rc = llc_conn_service(skb->sk, skb);
if (unlikely(rc != 0)) {
printk(KERN_ERR "%s: llc_conn_service failed\n", __func__);
- goto out_kfree_skb;
- }
-
- if (unlikely(!ev->ind_prim && !ev->cfm_prim)) {
- /* indicate or confirm not required */
- if (!skb->next)
- goto out_kfree_skb;
goto out_skb_put;
}

- if (unlikely(ev->ind_prim && ev->cfm_prim)) /* Paranoia */
- skb_get(skb);
-
switch (ev->ind_prim) {
case LLC_DATA_PRIM:
+ skb_get(skb);
llc_save_primitive(sk, skb, LLC_DATA_PRIM);
if (unlikely(sock_queue_rcv_skb(sk, skb))) {
/*
@@ -108,6 +93,7 @@ int llc_conn_state_process(struct sock *sk, struct sk_buff *skb)
* skb->sk pointing to the newly created struct sock in
* llc_conn_handler. -acme
*/
+ skb_get(skb);
skb_queue_tail(&sk->sk_receive_queue, skb);
sk->sk_state_change(sk);
break;
@@ -123,7 +109,6 @@ int llc_conn_state_process(struct sock *sk, struct sk_buff *skb)
sk->sk_state_change(sk);
}
}
- kfree_skb(skb);
sock_put(sk);
break;
case LLC_RESET_PRIM:
@@ -132,14 +117,11 @@ int llc_conn_state_process(struct sock *sk, struct sk_buff *skb)
* RESET is not being notified to upper layers for now
*/
printk(KERN_INFO "%s: received a reset ind!\n", __func__);
- kfree_skb(skb);
break;
default:
- if (ev->ind_prim) {
+ if (ev->ind_prim)
printk(KERN_INFO "%s: received unknown %d prim!\n",
__func__, ev->ind_prim);
- kfree_skb(skb);
- }
/* No indication */
break;
}
@@ -181,15 +163,12 @@ int llc_conn_state_process(struct sock *sk, struct sk_buff *skb)
printk(KERN_INFO "%s: received a reset conf!\n", __func__);
break;
default:
- if (ev->cfm_prim) {
+ if (ev->cfm_prim)
printk(KERN_INFO "%s: received unknown %d prim!\n",
__func__, ev->cfm_prim);
- break;
- }
- goto out_skb_put; /* No confirmation */
+ /* No confirmation */
+ break;
}
-out_kfree_skb:
- kfree_skb(skb);
out_skb_put:
kfree_skb(skb);
return rc;
--
2.20.1