[PATCH -stable,4.19.x 28/40] netfilter: nftables: exthdr: fix 4-byte stack OOB write

Pablo Neira Ayuso
2024-06-13T01:02:36Z

From: Florian Westphal <fw@strlen.de>

commit fd94d9dadee58e09b49075240fe83423eb1dcd36 upstream.

If priv->len is a multiple of 4, then dst[len / 4] can write past
the destination array which leads to stack corruption.

This construct is necessary to clean the remainder of the register
in case ->len is NOT a multiple of the register size, so make it
conditional just like nft_payload.c does.

The bug was added in 4.1 cycle and then copied/inherited when
tcp/sctp and ip option support was added.

Bug reported by Zero Day Initiative project (ZDI-CAN-21950,
ZDI-CAN-21951, ZDI-CAN-21961).

Fixes: 49499c3e6e18 ("netfilter: nf_tables: switch registers to 32 bit addressing")
Fixes: 935b7f643018 ("netfilter: nft_exthdr: add TCP option matching")
Fixes: 133dc203d77d ("netfilter: nft_exthdr: Support SCTP chunks")
Fixes: dbb5281a1f84 ("netfilter: nf_tables: add support for matching IPv4 options")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
net/netfilter/nft_exthdr.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c
index 8d0f14cd7cc3..847abad9ee7f 100644
--- a/net/netfilter/nft_exthdr.c
+++ b/net/netfilter/nft_exthdr.c
@@ -36,6 +36,14 @@ static unsigned int optlen(const u8 *opt, unsigned int offset)
return opt[offset + 1];
}

+static int nft_skb_copy_to_reg(const struct sk_buff *skb, int offset, u32 *dest, unsigned int len)
+{
+ if (len % NFT_REG32_SIZE)
+ dest[len / NFT_REG32_SIZE] = 0;
+
+ return skb_copy_bits(skb, offset, dest, len);
+}
+
static void nft_exthdr_ipv6_eval(const struct nft_expr *expr,
struct nft_regs *regs,
const struct nft_pktinfo *pkt)
@@ -57,8 +65,7 @@ static void nft_exthdr_ipv6_eval(const struct nft_expr *expr,
}
offset += priv->offset;

- dest[priv->len / NFT_REG32_SIZE] = 0;
- if (skb_copy_bits(pkt->skb, offset, dest, priv->len) < 0)
+ if (nft_skb_copy_to_reg(pkt->skb, offset, dest, priv->len) < 0)
goto err;
return;
err:
@@ -114,7 +121,8 @@ static void nft_exthdr_tcp_eval(const struct nft_expr *expr,
if (priv->flags & NFT_EXTHDR_F_PRESENT) {
*dest = 1;
} else {
- dest[priv->len / NFT_REG32_SIZE] = 0;
+ if (priv->len % NFT_REG32_SIZE)
+ dest[priv->len / NFT_REG32_SIZE] = 0;
memcpy(dest, opt + offset, priv->len);
}

--
2.30.2