net/sched: cls_u32: Fix reference counter leak leading to overflow

commit 04c55383fa5689357bcdd2c8036725a55ed632bc upstream.

In the event of a failure in tcf_change_indev(), u32_set_parms() will
immediately return without decrementing the recently incremented
reference counter.  If this happens enough times, the counter will
rollover and the reference freed, leading to a double free which can be
used to do 'bad things'.

In order to prevent this, move the point of possible failure above the
point where the reference counter is incremented.  Also save any
meaningful return values to be applied to the return data at the
appropriate point in time.

This issue was caught with KASAN.

Fixes: 705c7091262d ("net: sched: cls_u32: no need to call tcf_exts_change for newly allocated struct")
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Rishabh Bhatnagar <risbhat@amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index fdbdcba44917eafb611837c860e4a0ab64151569..a4e01220a53a17da60e57d97d5b3e586c6bf691f 100644 (file)
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -774,11 +774,22 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
                         struct nlattr *est, bool ovr)
 {
        int err;
+#ifdef CONFIG_NET_CLS_IND
+       int ifindex = -1;
+#endif
 
        err = tcf_exts_validate(net, tp, tb, est, &n->exts, ovr);
        if (err < 0)
                return err;
 
+#ifdef CONFIG_NET_CLS_IND
+       if (tb[TCA_U32_INDEV]) {
+               ifindex = tcf_change_indev(net, tb[TCA_U32_INDEV]);
+               if (ifindex < 0)
+                       return -EINVAL;
+       }
+#endif
+
        if (tb[TCA_U32_LINK]) {
                u32 handle = nla_get_u32(tb[TCA_U32_LINK]);
                struct tc_u_hnode *ht_down = NULL, *ht_old;
@@ -806,14 +817,10 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
        }
 
 #ifdef CONFIG_NET_CLS_IND
-       if (tb[TCA_U32_INDEV]) {
-               int ret;
-               ret = tcf_change_indev(net, tb[TCA_U32_INDEV]);
-               if (ret < 0)
-                       return -EINVAL;
-               n->ifindex = ret;
-       }
+       if (ifindex >= 0)
+               n->ifindex = ifindex;
 #endif
+
        return 0;
 }