On Wed, May 30, 2018 at 2:52 AM, Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote: > On Tue, May 29, 2018 at 05:35:25PM -0700, Kees Cook wrote: >> In the quest to remove all stack VLA usage from the kernel[1], this >> allocates the maximum size expected for all possible attrs and adds >> a sanity-check to make sure nothing gets out of sync. >> >> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx >> >> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> >> --- >> net/netfilter/nfnetlink.c | 22 ++++++++++++++++++++-- >> 1 file changed, 20 insertions(+), 2 deletions(-) >> >> diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c >> index 03ead8a9e90c..0cb395f9627e 100644 >> --- a/net/netfilter/nfnetlink.c >> +++ b/net/netfilter/nfnetlink.c >> @@ -28,6 +28,7 @@ >> >> #include <net/netlink.h> >> #include <linux/netfilter/nfnetlink.h> >> +#include <linux/netfilter/nf_tables.h> >> >> MODULE_LICENSE("GPL"); >> MODULE_AUTHOR("Harald Welte <laforge@xxxxxxxxxxxxx>"); >> @@ -37,6 +38,11 @@ MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER); >> rcu_dereference_protected(table[(id)].subsys, \ >> lockdep_nfnl_is_held((id))) >> >> +#define NFTA_MAX_ATTR max(max(max(NFTA_CHAIN_MAX, NFTA_FLOWTABLE_MAX),\ >> + max(NFTA_OBJ_MAX, NFTA_RULE_MAX)), \ >> + max(NFTA_TABLE_MAX, \ >> + max(NFTA_SET_ELEM_LIST_MAX, NFTA_SET_MAX))) > > This is very specific of nftables, there are other nf subsystems using > nfnetlink that may go over this maximum attribute value (grep from > "struct nfnetlink_subsystem"). Oops, yes. I see that now. > To remove the VLA, I think we need an artificial maximum attribute > that reasonably large enough. git grep insanity: $ for i in $(git grep -A10 'static .*struct nfnetlink_subsystem' | \ grep '\.cb\b' | awk '{print $NF}' | cut -d, -f1) do git grep -A100 'static .*'"$i\b"; done | \ grep '\.attr_count\b' | awk -F= '{print $NF}' | \ sed -e 's/ //g' | cut -d, -f1 | sort -u and manual counting gets me: CTA_EXPECT_MAX 12 CTA_MAX 25 CTA_TIMEOUT_MAX 6 IPSET_ATTR_CMD_MAX 11 NFACCT_MAX 9 NFCTH_MAX 7 NFQA_CFG_MAX 6 NFQA_MAX 21 NFTA_CHAIN_MAX 10 NFTA_COMPAT_MAX 4 NFTA_OBJ_MAX 8 NFTA_RULE_MAX 10 NFTA_SET_ELEM_LIST_MAX 5 NFTA_SET_MAX 17 NFTA_TABLE_MAX 6 NFULA_CFG_MAX 7 NFULA_MAX 20 OSF_ATTR_MAX 2 How about 32? As Florian suggested, I'll add the check in nfnetlink_subsys_register() with a WARN(). -Kees -- Kees Cook Pixel Security -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
