Commit:     543821c6f5dea5221426eaf1eac98b100249c7ac
Parent:     40208d71e0c6b5f912b185e637272b6481fcef3f
Author:     Radu Rendec <[EMAIL PROTECTED]>
AuthorDate: Wed Nov 7 01:20:12 2007 -0800
Committer:  David S. Miller <[EMAIL PROTECTED]>
CommitDate: Wed Nov 7 04:11:45 2007 -0800

    [PKT_SCHED] CLS_U32: Fix endianness problem with u32 classifier hash masks.
    While trying to implement u32 hashes in my shaping machine I ran into
    a possible bug in the u32 hash/bucket computing algorithm
    The problem occurs only with hash masks that extend over the octet
    boundary, on little endian machines (where htonl() actually does
    Let's say that I would like to use 0x3fc0 as the hash mask. This means
    8 contiguous "1" bits starting at b6. With such a mask, the expected
    (and logical) behavior is to hash any address in, for instance, in bucket 0, then any address in in
    bucket 1, then in bucket 2 and so on.
    This is exactly what would happen on a big endian machine, but on
    little endian machines, what would actually happen with current
    implementation is 0x3fc0 being reversed (into 0xc03f0000) by htonl()
    in the userspace tool and then applied to 192.168.x.x in the u32
    classifier. When shifting right by 16 bits (rank of first "1" bit in
    the reversed mask) and applying the divisor mask (0xff for divisor
    256), what would actually remain is 0x3f applied on the "168" octet of
    the address.
    One could say is this can be easily worked around by taking endianness
    into account in userspace and supplying an appropriate mask (0xfc03)
    that would be turned into contiguous "1" bits when reversed
    (0x03fc0000). But the actual problem is the network address (inside
    the packet) not being converted to host order, but used as a
    host-order value when computing the bucket.
    Let's say the network address is written as n31 n30 ... n0, with n0
    being the least significant bit. When used directly (without any
    conversion) on a little endian machine, it becomes n7 ... n0 n8 ..n15
    etc in the machine's registers. Thus bits n7 and n8 would no longer be
    adjacent and and would no longer be
    The fix is to apply ntohl() on the hmask before computing fshift,
    and in u32_hash_fold() convert the packet data to host order before
    shifting down by fshift.
    With helpful feedback from Jamal Hadi Salim and Jarek Poplawski.
    Signed-off-by: David S. Miller <[EMAIL PROTECTED]>
 net/sched/cls_u32.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 9e98c6e..5317102 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -91,7 +91,7 @@ static struct tc_u_common *u32_list;
 static __inline__ unsigned u32_hash_fold(u32 key, struct tc_u32_sel *sel, u8 
-       unsigned h = (key & sel->hmask)>>fshift;
+       unsigned h = ntohl(key & sel->hmask)>>fshift;
        return h;
@@ -615,7 +615,7 @@ static int u32_change(struct tcf_proto *tp, unsigned long 
base, u32 handle,
        n->handle = handle;
        u8 i = 0;
-       u32 mask = s->hmask;
+       u32 mask = ntohl(s->hmask);
        if (mask) {
                while (!(mask & 1)) {
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