[PATCH 5.15 072/148] net: core: fix flow symmetric hash

Greg Kroah-Hartman
2022-09-26T13:29:51Z

From: Ludovic Cintrat <ludovic.cintrat@gatewatcher.com>

[ Upstream commit 64ae13ed478428135cddc2f1113dff162d8112d4 ]

__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: c3f8324188fa8 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/flow_dissector.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index bc50bd331d5b..1c34e2266578 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -1519,9 +1519,8 @@ static inline void __flow_hash_consistentify(struct flow_keys *keys)

switch (keys->control.addr_type) {
case FLOW_DISSECTOR_KEY_IPV4_ADDRS:
- addr_diff = (__force u32)keys->addrs.v4addrs.dst -
- (__force u32)keys->addrs.v4addrs.src;
- if (addr_diff < 0)
+ if ((__force u32)keys->addrs.v4addrs.dst <
+ (__force u32)keys->addrs.v4addrs.src)
swap(keys->addrs.v4addrs.src, keys->addrs.v4addrs.dst);

if ((__force u16)keys->ports.dst <
--
2.35.1