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Subject[PATCH] netfilter: cttimeout: remove VLA usage
In preparation to enabling -Wvla, remove VLA and replace it
with dynamic memory allocation.

From a security viewpoint, the use of Variable Length Arrays can be
a vector for stack overflow attacks. Also, in general, as the code
evolves it is easy to lose track of how big a VLA can get. Thus, we
can end up having segfaults that are hard to debug.

Also, fixed as part of the directive to remove all VLAs from
the kernel: https://lkml.org/lkml/2018/3/7/621

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
net/netfilter/nfnetlink_cttimeout.c | 26 +++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/net/netfilter/nfnetlink_cttimeout.c b/net/netfilter/nfnetlink_cttimeout.c
index 6819300..dcd7bd3 100644
--- a/net/netfilter/nfnetlink_cttimeout.c
+++ b/net/netfilter/nfnetlink_cttimeout.c
@@ -51,19 +51,27 @@ ctnl_timeout_parse_policy(void *timeouts,
const struct nf_conntrack_l4proto *l4proto,
struct net *net, const struct nlattr *attr)
{
+ struct nlattr **tb;
int ret = 0;

- if (likely(l4proto->ctnl_timeout.nlattr_to_obj)) {
- struct nlattr *tb[l4proto->ctnl_timeout.nlattr_max+1];
+ if (!l4proto->ctnl_timeout.nlattr_to_obj)
+ return 0;

- ret = nla_parse_nested(tb, l4proto->ctnl_timeout.nlattr_max,
- attr, l4proto->ctnl_timeout.nla_policy,
- NULL);
- if (ret < 0)
- return ret;
+ tb = kcalloc(l4proto->ctnl_timeout.nlattr_max + 1, sizeof(*tb),
+ GFP_KERNEL);

- ret = l4proto->ctnl_timeout.nlattr_to_obj(tb, net, timeouts);
- }
+ if (!tb)
+ return -ENOMEM;
+
+ ret = nla_parse_nested(tb, l4proto->ctnl_timeout.nlattr_max, attr,
+ l4proto->ctnl_timeout.nla_policy, NULL);
+ if (ret < 0)
+ goto err;
+
+ ret = l4proto->ctnl_timeout.nlattr_to_obj(tb, net, timeouts);
+
+err:
+ kfree(tb);
return ret;
}

--
2.7.4
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