From 9b7ea92b9e3feff2876f772ace01148b7406839c Mon Sep 17 00:00:00 2001 From: Phil Sutter Date: Wed, 4 Aug 2021 11:18:28 +0200 Subject: [PATCH] tc: u32: Fix key folding in sample option In between Linux kernel 2.4 and 2.6, key folding for hash tables changed in kernel space. When iproute2 dropped support for the older algorithm, the wrong code was removed and kernel 2.4 folding method remained in place. To get things functional for recent kernels again, restoring the old code alone was not sufficient - additional byteorder fixes were needed. While being at it, make use of ffs() and thereby align the code with how kernel determines the shift width. Fixes: 267480f55383c ("Backout the 2.4 utsname hash patch.") Signed-off-by: Phil Sutter Signed-off-by: Stephen Hemminger --- tc/f_u32.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/tc/f_u32.c b/tc/f_u32.c index 2ed5254a4..a5747f671 100644 --- a/tc/f_u32.c +++ b/tc/f_u32.c @@ -978,6 +978,13 @@ show_k: goto show_k; } +static __u32 u32_hash_fold(struct tc_u32_key *key) +{ + __u8 fshift = key->mask ? ffs(ntohl(key->mask)) - 1 : 0; + + return ntohl(key->val & key->mask) >> fshift; +} + static int u32_parse_opt(struct filter_util *qu, char *handle, int argc, char **argv, struct nlmsghdr *n) { @@ -1110,9 +1117,7 @@ static int u32_parse_opt(struct filter_util *qu, char *handle, } NEXT_ARG(); } - hash = sel2.keys[0].val & sel2.keys[0].mask; - hash ^= hash >> 16; - hash ^= hash >> 8; + hash = u32_hash_fold(&sel2.keys[0]); htid = ((hash % divisor) << 12) | (htid & 0xFFF00000); sample_ok = 1; continue; -- 2.47.2