Gentle ping...
This patch fixes a remotely triggerable kernel oops, and as such can
be viewed as a remote denial of service attack depending on the
netfilter rule setup.
On Wed, Jun 10, 2020 at 09:51:11PM +0100, Russell King wrote:
> 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@xxxxxxxxxxxxxxx>
> ---
> 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
>
>
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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