Re: [PATCH net] netfilter: nft_tunnel: fix geneve_opt type confusion addition

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Wed, Apr 02, 2025 at 09:18:44PM +0200, Pablo Neira Ayuso wrote:
> Hi,
> 
> On Thu, Apr 03, 2025 at 01:00:26AM +0800, Lin Ma wrote:
> > When handling multiple NFTA_TUNNEL_KEY_OPTS_GENEVE attributes, the
> > parsing logic should place every geneve_opt structure one by one
> > compactly. Hence, when deciding the next geneve_opt position, the
> > pointer addition should be in units of char *.
> > 
> > However, the current implementation erroneously does type conversion
> > before the addition, which will lead to heap out-of-bounds write.
> 
> Patch LGTM, I can take it through nf.git, I am preparing a pull
> request now.

Actually, this chunk is missing in this patch:

diff --git a/net/netfilter/nft_tunnel.c b/net/netfilter/nft_tunnel.c
index 2df4b2a02f27..2e40f575aed9 100644
--- a/net/netfilter/nft_tunnel.c
+++ b/net/netfilter/nft_tunnel.c
@@ -625,7 +625,7 @@ static int nft_tunnel_opts_dump(struct sk_buff *skb,
                if (!inner)
                        goto failure;
                while (opts->len > offset) {
-                       opt = (struct geneve_opt *)opts->u.data + offset;
+                       opt = (struct geneve_opt *)(opts->u.data + offset);
                        if (nla_put_be16(skb, NFTA_TUNNEL_KEY_GENEVE_CLASS,
                                         opt->opt_class) ||
                            nla_put_u8(skb, NFTA_TUNNEL_KEY_GENEVE_TYPE,

> > [    6.989857] ==================================================================
> > [    6.990293] BUG: KASAN: slab-out-of-bounds in nft_tunnel_obj_init+0x977/0xa70
> > [    6.990725] Write of size 124 at addr ffff888005f18974 by task poc/178
> > [    6.991162]
> > [    6.991259] CPU: 0 PID: 178 Comm: poc-oob-write Not tainted 6.1.132 #1
> > [    6.991655] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> > [    6.992281] Call Trace:
> > [    6.992423]  <TASK>
> > [    6.992586]  dump_stack_lvl+0x44/0x5c
> > [    6.992801]  print_report+0x184/0x4be
> > [    6.993790]  kasan_report+0xc5/0x100
> > [    6.994252]  kasan_check_range+0xf3/0x1a0
> > [    6.994486]  memcpy+0x38/0x60
> > [    6.994692]  nft_tunnel_obj_init+0x977/0xa70
> > [    6.995677]  nft_obj_init+0x10c/0x1b0
> > [    6.995891]  nf_tables_newobj+0x585/0x950
> > [    6.996922]  nfnetlink_rcv_batch+0xdf9/0x1020
> > [    6.998997]  nfnetlink_rcv+0x1df/0x220
> > [    6.999537]  netlink_unicast+0x395/0x530
> > [    7.000771]  netlink_sendmsg+0x3d0/0x6d0
> > [    7.001462]  __sock_sendmsg+0x99/0xa0
> > [    7.001707]  ____sys_sendmsg+0x409/0x450
> > [    7.002391]  ___sys_sendmsg+0xfd/0x170
> > [    7.003145]  __sys_sendmsg+0xea/0x170
> > [    7.004359]  do_syscall_64+0x5e/0x90
> > [    7.005817]  entry_SYSCALL_64_after_hwframe+0x6e/0xd8
> > [    7.006127] RIP: 0033:0x7ec756d4e407
> > [    7.006339] Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 faf
> > [    7.007364] RSP: 002b:00007ffed5d46760 EFLAGS: 00000202 ORIG_RAX: 000000000000002e
> > [    7.007827] RAX: ffffffffffffffda RBX: 00007ec756cc4740 RCX: 00007ec756d4e407
> > [    7.008223] RDX: 0000000000000000 RSI: 00007ffed5d467f0 RDI: 0000000000000003
> > [    7.008620] RBP: 00007ffed5d468a0 R08: 0000000000000000 R09: 0000000000000000
> > [    7.009039] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
> > [    7.009429] R13: 00007ffed5d478b0 R14: 00007ec756ee5000 R15: 00005cbd4e655cb8
> > 
> > Fix this bug with correct pointer addition and conversion.
> > 
> > Fixes: 925d844696d9 ("netfilter: nft_tunnel: add support for geneve opts")
> > Signed-off-by: Lin Ma <linma@zju.edu.cn>
> > ---
> >  net/netfilter/nft_tunnel.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/netfilter/nft_tunnel.c b/net/netfilter/nft_tunnel.c
> > index 681301b46aa4..2df4b2a02f27 100644
> > --- a/net/netfilter/nft_tunnel.c
> > +++ b/net/netfilter/nft_tunnel.c
> > @@ -341,7 +341,7 @@ static const struct nla_policy nft_tunnel_opts_geneve_policy[NFTA_TUNNEL_KEY_GEN
> >  static int nft_tunnel_obj_geneve_init(const struct nlattr *attr,
> >  				      struct nft_tunnel_opts *opts)
> >  {
> > -	struct geneve_opt *opt = (struct geneve_opt *)opts->u.data + opts->len;
> > +	struct geneve_opt *opt = (struct geneve_opt *)(opts->u.data + opts->len);
> >  	struct nlattr *tb[NFTA_TUNNEL_KEY_GENEVE_MAX + 1];
> >  	int err, data_len;
> >  
> > -- 
> > 2.17.1
> >