Commit cf43ae63 authored Apr 06, 2018 by Jack Ma Committed by Pablo Neira Ayuso Apr 11, 2018

netfilter: xt_connmark: Add bit mapping for bit-shift operation.



With the addition of bit-shift operations, we are able to shift
ct/skbmark based on user requirements. However, this change might also
cause the most left/right hand- side mark to be accidentially lost
during shift operations.

This patch adds the ability to 'grep' certain bits based on ctmask or
nfmask out of the original mark. Then, apply shift operations to achieve
a new mapping between ctmark and skb->mark.

For example: If someone would like save the fourth F bits of ctmark
0xFFF(F)000F into the seventh hexadecimal (0) skb->mark 0xABC000(0)E.

	new_targetmark = (ctmark & ctmask) >> 12;
	(new) skb->mark = (skb->mark &~nfmask) ^
        	           new_targetmark;

This will preserve the other bits that are not related to this
operation.

Fixes: 472a73e0 ("netfilter: xt_conntrack: Support bit-shifting for CONNMARK & MARK targets.")
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Jack Ma <jack.ma@alliedtelesis.co.nz>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

parent 3f1e53ab

net/netfilter/xt_connmark.c

+11 −8

Original line number	Diff line number	Diff line
		@@ -41,6 +41,7 @@ connmark_tg_shift(struct sk_buff *skb,
		u8 shift_bits, u8 shift_dir)
		{
		enum ip_conntrack_info ctinfo;
		u_int32_t new_targetmark;
		struct nf_conn *ct;
		u_int32_t newmark;

		@@ -61,24 +62,26 @@ connmark_tg_shift(struct sk_buff *skb,
		}
		break;
		case XT_CONNMARK_SAVE:
		newmark = (ct->mark & ~info->ctmask) ^
		(skb->mark & info->nfmask);
		new_targetmark = (skb->mark & info->nfmask);
		if (shift_dir == D_SHIFT_RIGHT)
		newmark >>= shift_bits;
		new_targetmark >>= shift_bits;
		else
		newmark <<= shift_bits;
		new_targetmark <<= shift_bits;
		newmark = (ct->mark & ~info->ctmask) ^
		new_targetmark;
		if (ct->mark != newmark) {
		ct->mark = newmark;
		nf_conntrack_event_cache(IPCT_MARK, ct);
		}
		break;
		case XT_CONNMARK_RESTORE:
		newmark = (skb->mark & ~info->nfmask) ^
		(ct->mark & info->ctmask);
		new_targetmark = (ct->mark & info->ctmask);
		if (shift_dir == D_SHIFT_RIGHT)
		newmark >>= shift_bits;
		new_targetmark >>= shift_bits;
		else
		newmark <<= shift_bits;
		new_targetmark <<= shift_bits;
		newmark = (skb->mark & ~info->nfmask) ^
		new_targetmark;
		skb->mark = newmark;
		break;
		}

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