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netfilter: nft_exthdr: Fix for unsafe packet data read

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While iterating through an SCTP packet's chunks, skb_header_pointer() is
called for the minimum expected chunk header size. If (that part of) the
skbuff is non-linear, the following memcpy() may read data past
temporary buffer '_sch'. Use skb_copy_bits() instead which does the
right thing in this situation.

Fixes: 133dc203d7 ("netfilter: nft_exthdr: Support SCTP chunks")
Suggested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Phil Sutter <phil@nwl.cc>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Phil Sutter 2021-06-08 11:40:57 +02:00 committed by Pablo Neira Ayuso
parent e2cf17d377
commit cf6b5ffdce
1 changed files with 3 additions and 1 deletions
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4
net/netfilter/nft_exthdr.c
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@ -327,7 +327,9 @@ static void nft_exthdr_sctp_eval(const struct nft_expr *expr,
break;
dest[priv->len / NFT_REG32_SIZE] = 0;
memcpy(dest, (char *)sch + priv->offset, priv->len);
if (skb_copy_bits(pkt->skb, offset + priv->offset,
dest, priv->len) < 0)
break;
return;
}
offset += SCTP_PAD4(ntohs(sch->length));