Skip to main content

Browse the archive

Revision 99f62a746066fa436aa15d4606a538569540db08 authored by Vladimir Oltean on 21 September 2020, 22:07:09 UTC, committed by David S. Miller on 22 September 2020, 00:37:44 UTC 
net: bridge: br_vlan_get_pvid_rcu() should dereference the VLAN group under RCU
 
When calling the RCU brother of br_vlan_get_pvid(), lockdep warns:

=============================
WARNING: suspicious RCU usage
5.9.0-rc3-01631-g13c17acb8e38-dirty #814 Not tainted
-----------------------------
net/bridge/br_private.h:1054 suspicious rcu_dereference_protected() usage!

Call trace:
 lockdep_rcu_suspicious+0xd4/0xf8
 __br_vlan_get_pvid+0xc0/0x100
 br_vlan_get_pvid_rcu+0x78/0x108

The warning is because br_vlan_get_pvid_rcu() calls nbp_vlan_group()
which calls rtnl_dereference() instead of rcu_dereference(). In turn,
rtnl_dereference() calls rcu_dereference_protected() which assumes
operation under an RCU write-side critical section, which obviously is
not the case here. So, when the incorrect primitive is used to access
the RCU-protected VLAN group pointer, READ_ONCE() is not used, which may
cause various unexpected problems.

I'm sad to say that br_vlan_get_pvid() and br_vlan_get_pvid_rcu() cannot
share the same implementation. So fix the bug by splitting the 2
functions, and making br_vlan_get_pvid_rcu() retrieve the VLAN groups
under proper locking annotations.

Fixes: 7582f5b70f9a ("bridge: add br_vlan_get_pvid_rcu()")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 parent 47cec3f
Raw File
gen_crc64table.c 
// SPDX-License-Identifier: GPL-2.0
/*
 * Generate lookup table for the table-driven CRC64 calculation.
 *
 * gen_crc64table is executed in kernel build time and generates
 * lib/crc64table.h. This header is included by lib/crc64.c for
 * the table-driven CRC64 calculation.
 *
 * See lib/crc64.c for more information about which specification
 * and polynomial arithmetic that gen_crc64table.c follows to
 * generate the lookup table.
 *
 * Copyright 2018 SUSE Linux.
 *   Author: Coly Li <colyli@suse.de>
 */
#include <inttypes.h>
#include <stdio.h>

#define CRC64_ECMA182_POLY 0x42F0E1EBA9EA3693ULL

static uint64_t crc64_table[256] = {0};

static void generate_crc64_table(void)
{
	uint64_t i, j, c, crc;

	for (i = 0; i < 256; i++) {
		crc = 0;
		c = i << 56;

		for (j = 0; j < 8; j++) {
			if ((crc ^ c) & 0x8000000000000000ULL)
				crc = (crc << 1) ^ CRC64_ECMA182_POLY;
			else
				crc <<= 1;
			c <<= 1;
		}

		crc64_table[i] = crc;
	}
}

static void print_crc64_table(void)
{
	int i;

	printf("/* this file is generated - do not edit */\n\n");
	printf("#include <linux/types.h>\n");
	printf("#include <linux/cache.h>\n\n");
	printf("static const u64 ____cacheline_aligned crc64table[256] = {\n");
	for (i = 0; i < 256; i++) {
		printf("\t0x%016" PRIx64 "ULL", crc64_table[i]);
		if (i & 0x1)
			printf(",\n");
		else
			printf(", ");
	}
	printf("};\n");
}

int main(int argc, char *argv[])
{
	generate_crc64_table();
	print_crc64_table();
	return 0;
}
back to top