[PATCH libnftnl 0/2] object: fix crashes with out-of-tree nft

[PATCH libnftnl 0/2] object: fix crashes with out-of-tree nft

[Florian Westphal]

While working on ct helper object support I encountered crashes in libnftnl.
This occurs when nft sets unknown object types not supported by libnftnl.

The two patches avoid segfaults in case unsupported types are requested.

[PATCH libnftnl 1/2] object: don't set NFTNL_OBJ_TYPE unless obj->ops is non-null

[Florian Westphal]

If nft sets an invalid type, nftnl_obj_ops_lookup will return NULL.
In this case we must not set NFTNL_OBJ_TYPE flag, else we later get
crash in nftnl_obj_nlmsg_build_payload as it dereferences obj->ops.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 src/object.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/object.c b/src/object.c
index 9594d2f99071..62fa48afa2a1 100644
--- a/src/object.c
+++ b/src/object.c
@@ -83,6 +83,8 @@ void nftnl_obj_set_data(struct nftnl_obj *obj, uint16_t attr,
 		break;
 	case NFTNL_OBJ_TYPE:
 		obj->ops = nftnl_obj_ops_lookup(*((uint32_t *)data));
+		if (!obj->ops)
+			return;
 		break;
 	case NFTNL_OBJ_FAMILY:
 		obj->family = *((uint32_t *)data);
@@ -250,7 +252,8 @@ int nftnl_obj_nlmsg_parse(const struct nlmsghdr *nlh, struct nftnl_obj *obj)
 		uint32_t type = ntohl(mnl_attr_get_u32(tb[NFTA_OBJ_TYPE]));
 
 		obj->ops = nftnl_obj_ops_lookup(type);
-		obj->flags |= (1 << NFTNL_OBJ_TYPE);
+		if (obj->ops)
+			obj->flags |= (1 << NFTNL_OBJ_TYPE);
 	}
 	if (tb[NFTA_OBJ_DATA]) {
 		if (obj->ops) {
-- 
2.10.2

Re: [PATCH libnftnl 1/2] object: don't set NFTNL_OBJ_TYPE unless obj->ops is non-null

[Pablo Neira Ayuso]

On Mon, Feb 27, 2017 at 03:56:09PM +0100, Florian Westphal wrote:
> If nft sets an invalid type, nftnl_obj_ops_lookup will return NULL.
> In this case we must not set NFTNL_OBJ_TYPE flag, else we later get
> crash in nftnl_obj_nlmsg_build_payload as it dereferences obj->ops.
> 
> Signed-off-by: Florian Westphal <fw@strlen.de>

Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>

[PATCH libnftnl 2/2] object: fix crash when object ops is null

[Florian Westphal]

when debugging nft with invalid object type (during development),
this will crash here with null deref.  Print (unknown) instead
if obj->ops is null.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 src/object.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/object.c b/src/object.c
index 62fa48afa2a1..773eff6a5a18 100644
--- a/src/object.c
+++ b/src/object.c
@@ -396,10 +396,11 @@ static int nftnl_obj_snprintf_dflt(char *buf, size_t size,
 				   const struct nftnl_obj *obj,
 				   uint32_t type, uint32_t flags)
 {
+	const char *name = obj->ops ? obj->ops->name : "(unknown)";
 	int ret, len = size, offset = 0;
 
 	ret = snprintf(buf, size, "table %s name %s use %u [ %s ",
-		       obj->table, obj->name, obj->use, obj->ops->name);
+		       obj->table, obj->name, obj->use, name);
 	SNPRINTF_BUFFER_SIZE(ret, size, len, offset);
 
 	if (obj->ops) {
-- 
2.10.2

Re: [PATCH libnftnl 2/2] object: fix crash when object ops is null

[Pablo Neira Ayuso]

On Mon, Feb 27, 2017 at 03:56:10PM +0100, Florian Westphal wrote:
> when debugging nft with invalid object type (during development),
> this will crash here with null deref.  Print (unknown) instead
> if obj->ops is null.
> 
> Signed-off-by: Florian Westphal <fw@strlen.de>

Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>

Thanks Florian.