Commit 28a97c43 authored Jun 13, 2024 by Florian Westphal Committed by Greg Kroah-Hartman Jun 16, 2024

netfilter: nftables: exthdr: fix 4-byte stack OOB write



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: 49499c3e ("netfilter: nf_tables: switch registers to 32 bit addressing")
Fixes: 935b7f64 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 6a67f972

net/netfilter/nft_exthdr.c

+11 −3

Original line number	Diff line number	Diff line
		@@ -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:
		@@ -114,6 +121,7 @@ static void nft_exthdr_tcp_eval(const struct nft_expr *expr,
		if (priv->flags & NFT_EXTHDR_F_PRESENT) {
		*dest = 1;
		} else {
		if (priv->len % NFT_REG32_SIZE)
		dest[priv->len / NFT_REG32_SIZE] = 0;
		memcpy(dest, opt + offset, priv->len);
		}