[PATCH 4.19 24/88] netfilter: nf_tables: fix destination register zeroing

Greg Kroah-Hartman
2020-09-08T18:41:44Z

From: Florian Westphal <fw@strlen.de>

[ Upstream commit 1e105e6afa6c3d32bfb52c00ffa393894a525c27 ]

Following bug was reported via irc:
nft list ruleset
set knock_candidates_ipv4 {
type ipv4_addr . inet_service
size 65535
elements = { 127.0.0.1 . 123,
127.0.0.1 . 123 }
}
..
udp dport 123 add @knock_candidates_ipv4 { ip saddr . 123 }
udp dport 123 add @knock_candidates_ipv4 { ip saddr . udp dport }

It should not have been possible to add a duplicate set entry.

After some debugging it turned out that the problem is the immediate
value (123) in the second-to-last rule.

Concatenations use 32bit registers, i.e. the elements are 8 bytes each,
not 6 and it turns out the kernel inserted

inet firewall @knock_candidates_ipv4
element 0100007f ffff7b00 : 0 [end]
element 0100007f 00007b00 : 0 [end]

Note the non-zero upper bits of the first element. It turns out that
nft_immediate doesn't zero the destination register, but this is needed
when the length isn't a multiple of 4.

Furthermore, the zeroing in nft_payload is broken. We can't use
[len / 4] = 0 -- if len is a multiple of 4, index is off by one.

Skip zeroing in this case and use a conditional instead of (len -1) / 4.

Fixes: 49499c3e6e18 ("netfilter: nf_tables: switch registers to 32 bit addressing")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/netfilter/nf_tables.h | 2 ++
net/netfilter/nft_payload.c | 4 +++-
2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index 024636c31adcf..93253ba1eeac3 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -130,6 +130,8 @@ static inline u8 nft_reg_load8(u32 *sreg)
static inline void nft_data_copy(u32 *dst, const struct nft_data *src,
unsigned int len)
{
+ if (len % NFT_REG32_SIZE)
+ dst[len / NFT_REG32_SIZE] = 0;
memcpy(dst, src, len);
}

diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
index 19446a89a2a81..b1a9f330a51fe 100644
--- a/net/netfilter/nft_payload.c
+++ b/net/netfilter/nft_payload.c
@@ -79,7 +79,9 @@ static void nft_payload_eval(const struct nft_expr *expr,
u32 *dest = &regs->data[priv->dreg];
int offset;

- dest[priv->len / NFT_REG32_SIZE] = 0;
+ if (priv->len % NFT_REG32_SIZE)
+ dest[priv->len / NFT_REG32_SIZE] = 0;
+
switch (priv->base) {
case NFT_PAYLOAD_LL_HEADER:
if (!skb_mac_header_was_set(skb))
--
2.25.1