netdev - [PATCH net] net/sched: act_simple: don't leak 'index' in the error path

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Date:   Wed, 14 Mar 2018 03:13:01 +0100
From:   Davide Caratti <dcaratti@...hat.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org
Subject: [PATCH net] net/sched: act_simple: don't leak 'index' in the error path

if the kernel fails duplicating 'sdata', creation of a new action fails
with -ENOMEM. However, subsequent attempts to install the same action
using the same value of 'index' will systematically fail with -ENOSPC,
and that value of 'index' will no more be usable by act_simple, until
rmmod / insmod of act_simple.ko is done:

 # tc actions add action simple sdata hello index 100
 # tc actions list action simple

        action order 0: Simple <hello>
         index 100 ref 1 bind 0
 # tc actions flush action simple
 # tc actions add action simple sdata hello index 100
RTNETLINK answers: Cannot allocate memory
We have an error talking to the kernel
 # tc actions flush action simple
 # tc actions add action simple sdata hello index 100
RTNETLINK answers: No space left on device
We have an error talking to the kernel
 # tc actions add action simple sdata hello index 100
RTNETLINK answers: No space left on device
We have an error talking to the kernel
 ...

Similarly to what other TC actions do, we can duplicate 'sdata' before
calling tcf_idr_create(), and avoid calling tcf_idr_cleanup(), so that
leaks of 'index' don't occur anymore.

Signed-off-by: Davide Caratti <dcaratti@...hat.com>
---

Notes:
    Hello,
    
    I observed this faulty behavior on act_bpf, in case of negative return
    value of tcf_bpf_init_from_ops() and tcf_bpf_init_from_efd(). Then I
    tried on act_simple, that parses its parameter in a similar way, and
    reproduced the same leakage of 'index'.
    
    So, unless you think we should fix this issue in a different way (i.e.
    changing tcf_idr_cleanup() ), I will post a similar fix for act_bpf.
    
    Any feedback is welcome, thank you in advance!

 net/sched/act_simple.c | 22 ++++++----------------
 1 file changed, 6 insertions(+), 16 deletions(-)

diff --git a/net/sched/act_simple.c b/net/sched/act_simple.c
index 425eac11f6da..b80d4a69a848 100644
--- a/net/sched/act_simple.c
+++ b/net/sched/act_simple.c
@@ -53,15 +53,6 @@ static void tcf_simp_release(struct tc_action *a)
 	kfree(d->tcfd_defdata);
 }
 
-static int alloc_defdata(struct tcf_defact *d, char *defdata)
-{
-	d->tcfd_defdata = kzalloc(SIMP_MAX_DATA, GFP_KERNEL);
-	if (unlikely(!d->tcfd_defdata))
-		return -ENOMEM;
-	strlcpy(d->tcfd_defdata, defdata, SIMP_MAX_DATA);
-	return 0;
-}
-
 static void reset_policy(struct tcf_defact *d, char *defdata,
 			 struct tc_defact *p)
 {
@@ -110,20 +101,18 @@ static int tcf_simp_init(struct net *net, struct nlattr *nla,
 		return -EINVAL;
 	}
 
-	defdata = nla_data(tb[TCA_DEF_DATA]);
-
 	if (!exists) {
+		defdata = nla_strdup(tb[TCA_DEF_DATA], GFP_KERNEL);
+		if (unlikely(!defdata))
+			return -ENOMEM;
+
 		ret = tcf_idr_create(tn, parm->index, est, a,
 				     &act_simp_ops, bind, false);
 		if (ret)
 			return ret;
 
 		d = to_defact(*a);
-		ret = alloc_defdata(d, defdata);
-		if (ret < 0) {
-			tcf_idr_cleanup(*a, est);
-			return ret;
-		}
+		d->tcfd_defdata = defdata;
 		d->tcf_action = parm->action;
 		ret = ACT_P_CREATED;
 	} else {
@@ -133,6 +122,7 @@ static int tcf_simp_init(struct net *net, struct nlattr *nla,
 		if (!ovr)
 			return -EEXIST;
 
+		defdata = nla_data(tb[TCA_DEF_DATA]);
 		reset_policy(d, defdata, parm);
 	}
 
-- 
2.14.3