netdev - [PATCH v1] netfilter: nf_tables: fix nft_set_elem

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Date:   Sat, 2 Jul 2022 19:59:11 +0200
From:   Hugues ANGUELKOV <hanguelkov@...dorisec.fr>
To:     netdev@...r.kernel.org
Cc:     security@...nel.org, pablo@...filter.org, kadlec@...filter.org,
        fw@...len.de, davy <davy@...dorisec.fr>, amongodin@...dorisec.fr,
        kuba@...nel.org, torvalds@...uxfoundation.org
Subject: [PATCH v1] netfilter: nf_tables: fix nft_set_elem_init heap buffer
 overflow

>From d91007a18140e02a1f12c9627058a019fe55b8e6 Mon Sep 17 00:00:00 2001
From: Arthur Mongodin <amongodin@...dorisec.fr>
Date: Sat, 2 Jul 2022 17:11:48 +0200
Subject: [PATCH v1] netfilter: nf_tables: fix nft_set_elem_init heap buffer
 overflow

The length used for the memcpy in nft_set_elem_init may exceed the bound
of the allocated object due to a weak check in nft_setelem_parse_data.
As a user can add an element with a data type NFT_DATA_VERDICT to a set
with a data type different of NFT_DATA_VERDICT, then the comparison on the
data type of the element allows to avoid the comparaison on the data length
This fix forces the length comparison in nft_setelem_parse_data by removing
the check for NFT_DATA_VERDICT type.

====

BUG: KASAN: slab-out-of-bounds in nft_set_elem_init+0x158/0x1f0
Write of size 64 at addr ffff888007f717b0 by task poc/264

Call Trace:
 <TASK>
 dump_stack_lvl+0x3a/0x4c
 print_report.cold+0x5e/0x5e7
 ? nft_set_elem_init+0x158/0x1f0
 kasan_report+0xaa/0x120
 ? nft_set_elem_init+0x158/0x1f0
 kasan_check_range+0x160/0x1c0
 memcpy+0x3b/0x60
 nft_set_elem_init+0x158/0x1f0
 ...

Allocated by task 264:
 kasan_save_stack+0x26/0x50
 __kasan_kmalloc+0x95/0xc0
 __kmalloc+0x29a/0x4d0
 nft_set_elem_init+0x68/0x1f0
 ...

Fixes: fdb9c405e35b ("netfilter: nf_tables: allow up to 64 bytes in the set element data area")
Signed-off-by: Arthur Mongodin <amongodin@...dorisec.fr>
---
 net/netfilter/nf_tables_api.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index 51144fc66889..07845f211f3e 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -5219,7 +5219,7 @@ static int nft_setelem_parse_data(struct nft_ctx *ctx, struct nft_set *set,
 	if (err < 0)
 		return err;

-	if (desc->type != NFT_DATA_VERDICT && desc->len != set->dlen) {
+	if (desc->len != set->dlen) {
 		nft_data_release(data, desc->type);
 		return -EINVAL;
 	}
-- 
2.36.1