[PATCH nf-next,v2] netfilter: nft_compat: do not dump private area

[Pablo Neira Ayuso]

Zero pad private area, otherwise we expose private kernel pointer to
userspace. This patch also zeroes the tail area after the ->matchsize
and ->targetsize that results from XT_ALIGN().

Fixes: 0ca743a55991 ("netfilter: nf_tables: add compatibility layer for 
x_tables")
Reported-by: Florian Westphal <f...@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pa...@netfilter.org>
---
v2: add nft_extension_dump_info() to avoid code duplication.

 net/netfilter/nft_compat.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nft_compat.c b/net/netfilter/nft_compat.c
index 32535eea51b2..768292eac2a4 100644
--- a/net/netfilter/nft_compat.c
+++ b/net/netfilter/nft_compat.c
@@ -290,6 +290,24 @@ nft_target_destroy(const struct nft_ctx *ctx, const struct 
nft_expr *expr)
                module_put(target->me);
 }
 
+static int nft_extension_dump_info(struct sk_buff *skb, int attr,
+                                  const void *info,
+                                  unsigned int size, unsigned int user_size)
+{
+       unsigned int info_size, aligned_size = XT_ALIGN(size);
+       struct nlattr *nla;
+
+       nla = nla_reserve(skb, attr, aligned_size);
+       if (!nla)
+               return -1;
+
+       info_size = user_size ? : size;
+       memcpy(nla_data(nla), info, info_size);
+       memset(nla_data(nla) + info_size, 0, aligned_size - info_size);
+
+       return 0;
+}
+
 static int nft_target_dump(struct sk_buff *skb, const struct nft_expr *expr)
 {
        const struct xt_target *target = expr->ops->data;
@@ -297,7 +315,8 @@ static int nft_target_dump(struct sk_buff *skb, const 
struct nft_expr *expr)
 
        if (nla_put_string(skb, NFTA_TARGET_NAME, target->name) ||
            nla_put_be32(skb, NFTA_TARGET_REV, htonl(target->revision)) ||
-           nla_put(skb, NFTA_TARGET_INFO, XT_ALIGN(target->targetsize), info))
+           nft_extension_dump_info(skb, NFTA_TARGET_INFO, info,
+                                   target->targetsize, target->usersize))
                goto nla_put_failure;
 
        return 0;
@@ -532,7 +551,8 @@ static int __nft_match_dump(struct sk_buff *skb, const 
struct nft_expr *expr,
 
        if (nla_put_string(skb, NFTA_MATCH_NAME, match->name) ||
            nla_put_be32(skb, NFTA_MATCH_REV, htonl(match->revision)) ||
-           nla_put(skb, NFTA_MATCH_INFO, XT_ALIGN(match->matchsize), info))
+           nft_extension_dump_info(skb, NFTA_MATCH_INFO, info,
+                                   match->matchsize, match->usersize))
                goto nla_put_failure;
 
        return 0;
-- 
2.11.0