net: core: fix flow symmetric hash
__flow_hash_consistentify() wrongly swaps ipv4 addresses in few cases. This function is indirectly used by __skb_get_hash_symmetric(), which is used to fanout packets in AF_PACKET. Intrusion detection systems may be impacted by this issue. __flow_hash_consistentify() computes the addresses difference then swaps them if the difference is negative. In few cases src - dst and dst - src are both negative. The following snippet mimics __flow_hash_consistentify(): ``` #include <stdio.h> #include <stdint.h> int main(int argc, char** argv) { int diffs_d, diffd_s; uint32_t dst = 0xb225a8c0; /* 178.37.168.192 --> 192.168.37.178 */ uint32_t src = 0x3225a8c0; /* 50.37.168.192 --> 192.168.37.50 */ uint32_t dst2 = 0x3325a8c0; /* 51.37.168.192 --> 192.168.37.51 */ diffs_d = src - dst; diffd_s = dst - src; printf("src:%08x dst:%08x, diff(s-d)=%d(0x%x) diff(d-s)=%d(0x%x)\n", src, dst, diffs_d, diffs_d, diffd_s, diffd_s); diffs_d = src - dst2; diffd_s = dst2 - src; printf("src:%08x dst:%08x, diff(s-d)=%d(0x%x) diff(d-s)=%d(0x%x)\n", src, dst2, diffs_d, diffs_d, diffd_s, diffd_s); return 0; } ``` Results: src:3225a8c0 dst:b225a8c0, \ diff(s-d)=-2147483648(0x80000000) \ diff(d-s)=-2147483648(0x80000000) src:3225a8c0 dst:3325a8c0, \ diff(s-d)=-16777216(0xff000000) \ diff(d-s)=16777216(0x1000000) In the first case the addresses differences are always < 0, therefore __flow_hash_consistentify() always swaps, thus dst->src and src->dst packets have differents hashes. Fixes: c3f83241 ("net: Add full IPv6 addresses to flow_keys") Signed-off-by:Ludovic Cintrat <ludovic.cintrat@gatewatcher.com> Signed-off-by:
David S. Miller <davem@davemloft.net>
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