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Message-ID: <9b41e3b1-119a-4180-3f11-14ef36592dd6@oracle.com>
Date: Sun, 21 Aug 2022 00:50:58 +0530
From: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
To: Florian Westphal <fw@...len.de>, netfilter-devel@...r.kernel.org
Cc: syzkaller@...glegroups.com, george.kennedy@...cle.com,
vegard.nossum@...cle.com, john.p.donnelly@...cle.com,
bridge@...ts.linux-foundation.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [External] : [PATCH nf] netfilter: ebtables: reject blobs that
don't provide all entry points
Hi Florian,
On 20/08/22 11:05 pm, Florian Westphal wrote:
> For some reason ebtables reject blobs that provide entry points that are
> not supported by the table.
>
> What it should instead reject is the opposite, i.e. rulesets that
> DO NOT provide an entry point that is supported by the table.
>
> t->valid_hooks is the bitmask of hooks (input, forward ...) that will
> see packets. So, providing an entry point that is not support is
> harmless (never called/used), but the reverse is NOT, this will cause
> crash because the ebtables traverser doesn't expect a NULL blob for
> a location its receiving packets for.
>
> Instead of fixing all the individual checks, do what iptables is doing and
> reject all blobs that doesn't provide the expected hooks.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
> Signed-off-by: Florian Westphal <fw@...len.de>
> ---
> Harshit, can you check if this also silences your reproducer?
>
Thanks for the patch, I have run the reproducer on patched kernel(this
patch) multiple times and the problem is not seen. So it silences the
reproducer.
Regards,
Harshit
> Thanks!
>
> include/linux/netfilter_bridge/ebtables.h | 4 ----
> net/bridge/netfilter/ebtable_broute.c | 8 --------
> net/bridge/netfilter/ebtable_filter.c | 8 --------
> net/bridge/netfilter/ebtable_nat.c | 8 --------
> net/bridge/netfilter/ebtables.c | 8 +-------
> 5 files changed, 1 insertion(+), 35 deletions(-)
>
> diff --git a/include/linux/netfilter_bridge/ebtables.h b/include/linux/netfilter_bridge/ebtables.h
> index a13296d6c7ce..fd533552a062 100644
> --- a/include/linux/netfilter_bridge/ebtables.h
> +++ b/include/linux/netfilter_bridge/ebtables.h
> @@ -94,10 +94,6 @@ struct ebt_table {
> struct ebt_replace_kernel *table;
> unsigned int valid_hooks;
> rwlock_t lock;
> - /* e.g. could be the table explicitly only allows certain
> - * matches, targets, ... 0 == let it in */
> - int (*check)(const struct ebt_table_info *info,
> - unsigned int valid_hooks);
> /* the data used by the kernel */
> struct ebt_table_info *private;
> struct nf_hook_ops *ops;
> diff --git a/net/bridge/netfilter/ebtable_broute.c b/net/bridge/netfilter/ebtable_broute.c
> index 1a11064f9990..8f19253024b0 100644
> --- a/net/bridge/netfilter/ebtable_broute.c
> +++ b/net/bridge/netfilter/ebtable_broute.c
> @@ -36,18 +36,10 @@ static struct ebt_replace_kernel initial_table = {
> .entries = (char *)&initial_chain,
> };
>
> -static int check(const struct ebt_table_info *info, unsigned int valid_hooks)
> -{
> - if (valid_hooks & ~(1 << NF_BR_BROUTING))
> - return -EINVAL;
> - return 0;
> -}
> -
> static const struct ebt_table broute_table = {
> .name = "broute",
> .table = &initial_table,
> .valid_hooks = 1 << NF_BR_BROUTING,
> - .check = check,
> .me = THIS_MODULE,
> };
>
> diff --git a/net/bridge/netfilter/ebtable_filter.c b/net/bridge/netfilter/ebtable_filter.c
> index cb949436bc0e..278f324e6752 100644
> --- a/net/bridge/netfilter/ebtable_filter.c
> +++ b/net/bridge/netfilter/ebtable_filter.c
> @@ -43,18 +43,10 @@ static struct ebt_replace_kernel initial_table = {
> .entries = (char *)initial_chains,
> };
>
> -static int check(const struct ebt_table_info *info, unsigned int valid_hooks)
> -{
> - if (valid_hooks & ~FILTER_VALID_HOOKS)
> - return -EINVAL;
> - return 0;
> -}
> -
> static const struct ebt_table frame_filter = {
> .name = "filter",
> .table = &initial_table,
> .valid_hooks = FILTER_VALID_HOOKS,
> - .check = check,
> .me = THIS_MODULE,
> };
>
> diff --git a/net/bridge/netfilter/ebtable_nat.c b/net/bridge/netfilter/ebtable_nat.c
> index 5ee0531ae506..9066f7f376d5 100644
> --- a/net/bridge/netfilter/ebtable_nat.c
> +++ b/net/bridge/netfilter/ebtable_nat.c
> @@ -43,18 +43,10 @@ static struct ebt_replace_kernel initial_table = {
> .entries = (char *)initial_chains,
> };
>
> -static int check(const struct ebt_table_info *info, unsigned int valid_hooks)
> -{
> - if (valid_hooks & ~NAT_VALID_HOOKS)
> - return -EINVAL;
> - return 0;
> -}
> -
> static const struct ebt_table frame_nat = {
> .name = "nat",
> .table = &initial_table,
> .valid_hooks = NAT_VALID_HOOKS,
> - .check = check,
> .me = THIS_MODULE,
> };
>
> diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
> index f2dbefb61ce8..9a0ae59cdc50 100644
> --- a/net/bridge/netfilter/ebtables.c
> +++ b/net/bridge/netfilter/ebtables.c
> @@ -1040,8 +1040,7 @@ static int do_replace_finish(struct net *net, struct ebt_replace *repl,
> goto free_iterate;
> }
>
> - /* the table doesn't like it */
> - if (t->check && (ret = t->check(newinfo, repl->valid_hooks)))
> + if (repl->valid_hooks != t->valid_hooks)
> goto free_unlock;
>
> if (repl->num_counters && repl->num_counters != t->private->nentries) {
> @@ -1231,11 +1230,6 @@ int ebt_register_table(struct net *net, const struct ebt_table *input_table,
> if (ret != 0)
> goto free_chainstack;
>
> - if (table->check && table->check(newinfo, table->valid_hooks)) {
> - ret = -EINVAL;
> - goto free_chainstack;
> - }
> -
> table->private = newinfo;
> rwlock_init(&table->lock);
> mutex_lock(&ebt_mutex);
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