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 Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org --- Hi Greg, Sasha,

This backport is missing in 5.4, please apply to -stable. Thanks.

net/netfilter/nft_exthdr.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c index 670dd146fb2b..ca268293cfa1 100644 --- a/net/netfilter/nft_exthdr.c +++ b/net/netfilter/nft_exthdr.c @@ -33,6 +33,14 @@ 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) @@ -54,8 +62,7 @@ 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: @@ -151,8 +158,7 @@ static void nft_exthdr_ipv4_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: @@ -208,7 +214,8 @@ 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); }