On Friday 30 September 2016, Eric Dumazet wrote:

On Fri, 2016-09-30 at 18:05 +0200, Arnd Bergmann wrote:

quoted

 net/netfilter/xt_hashlimit.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 44a095ecc7b7..3d5525df6eb3 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c

@@ -464,20 +464,23 @@ static u32 xt_hashlimit_len_to_chunks(u32 len)
 static u64 user2credits(u64 user, int revision)
 {
 	if (revision == 1) {
+		u32 user32 = user; /* use 32-bit division */
+

This looks dangerous to me. Have you really tried all possible cases ?

Yes, I'm pretty certain about that: The 11d5f15723c9 patch that introduced this
kept the existing implementation for the revision==1 case, except for changing
the types.

Caller (even if using revision == 1) does
user2credits(cfg->avg * cfg->burst, revision);

Since this is not a fast path, I would prefer to keep the 64bit divide.

Vishwanath version looks safer.

Ok, fair enough. I couldn't tell how much of a fast path this
was, and it's more a general issue that I see with other developers
blindly using div_u64() whenever getting this link error.

Since I already had the patch by the time I saw the other one
(which is also at v3 and got comments), I just sent it out along
with the other two patches I had for netfilter.

I also ended up introducing a typo in a last-minute change, so I'll let
Vishwanath and you work out the best implementation and withdraw my
version.

	Arnd