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: 472a73e00757 ("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>

diff --git a/net/netfilter/xt_connmark.c b/net/netfilter/xt_connmark.c
index 773da82190dc32afc82d9b3a2d792f92660a4612..4b424e6caf3ec9da775d271b5445e5d4fe198d0f 100644 (file)
--- a/net/netfilter/xt_connmark.c
+++ b/net/netfilter/xt_connmark.c
@@ -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;
        }