Patch "netfilter: nftables: exthdr: fix 4-byte stack OOB write" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

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

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     netfilter-nftables-exthdr-fix-4-byte-stack-oob-write.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit fd14d75508aec873f251f77bab8efdd31788ea96
Author: Florian Westphal <fw@xxxxxxxxx>
Date:   Tue Sep 5 23:13:56 2023 +0200

    netfilter: nftables: exthdr: fix 4-byte stack OOB write
    
    [ Upstream commit fd94d9dadee58e09b49075240fe83423eb1dcd36 ]
    
    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@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c
index 9e927ab4df151..3609680831a14 100644
--- a/net/netfilter/nft_exthdr.c
+++ b/net/netfilter/nft_exthdr.c
@@ -35,6 +35,14 @@ 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)
@@ -56,8 +64,7 @@ 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:
@@ -153,8 +160,7 @@ 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:
@@ -210,7 +216,8 @@ 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);
 		}
 
@@ -335,9 +342,8 @@ static void nft_exthdr_sctp_eval(const struct nft_expr *expr,
 			    offset + ntohs(sch->length) > pkt->skb->len)
 				break;
 
-			dest[priv->len / NFT_REG32_SIZE] = 0;
-			if (skb_copy_bits(pkt->skb, offset + priv->offset,
-					  dest, priv->len) < 0)
+			if (nft_skb_copy_to_reg(pkt->skb, offset + priv->offset,
+						dest, priv->len) < 0)
 				break;
 			return;
 		}