netdev - [PATCH] netfiler: ipset: fix unaligned atomic access

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Date:   Wed, 10 Jun 2020 21:51:11 +0100
From:   Russell King <rmk+kernel@...linux.org.uk>
To:     coreteam@...filter.org, netfilter-devel@...r.kernel.org
Cc:     Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Subject: [PATCH] netfiler: ipset: fix unaligned atomic access

When using ip_set with counters and comment, traffic causes the kernel
to panic on 32-bit ARM:

Alignment trap: not handling instruction e1b82f9f at [<bf01b0dc>]
Unhandled fault: alignment exception (0x221) at 0xea08133c
PC is at ip_set_match_extensions+0xe0/0x224 [ip_set]

The problem occurs when we try to update the 64-bit counters - the
faulting address above is not 64-bit aligned.  The problem occurs
due to the way elements are allocated, for example:

	set->dsize = ip_set_elem_len(set, tb, 0, 0);
	map = ip_set_alloc(sizeof(*map) + elements * set->dsize);

If the element has a requirement for a member to be 64-bit aligned,
and set->dsize is not a multiple of 8, but is a multiple of four,
then every odd numbered elements will be misaligned - and hitting
an atomic64_add() on that element will cause the kernel to panic.

ip_set_elem_len() must return a size that is rounded to the maximum
alignment of any extension field stored in the element.  This change
ensures that is the case.

Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
---
Patch against v5.6, where I tripped over this bug.  This bug has
caused a kernel panic on my new router twice today.

 net/netfilter/ipset/ip_set_core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/netfilter/ipset/ip_set_core.c b/net/netfilter/ipset/ip_set_core.c
index 8dd17589217d..be9cd6a500fb 100644
--- a/net/netfilter/ipset/ip_set_core.c
+++ b/net/netfilter/ipset/ip_set_core.c
@@ -459,6 +459,8 @@ ip_set_elem_len(struct ip_set *set, struct nlattr *tb[], size_t len,
 	for (id = 0; id < IPSET_EXT_ID_MAX; id++) {
 		if (!add_extension(id, cadt_flags, tb))
 			continue;
+		if (align < ip_set_extensions[id].align)
+			align = ip_set_extensions[id].align;
 		len = ALIGN(len, ip_set_extensions[id].align);
 		set->offset[id] = len;
 		set->extensions |= ip_set_extensions[id].type;
-- 
2.20.1