Re: [PATCH] net: sched: fix possible OOB write in fl_set_geneve_opt()

From: Hangyu Hua
Date: Wed May 31 2023 - 01:57:49 EST

On 30/5/2023 22:29, Pieter Jansen van Vuuren wrote:

On 30/05/2023 12:36, Simon Horman wrote:
[Updated Pieter's email address, dropped old email address of mine]

Thank you Simon.

On Mon, May 29, 2023 at 12:36:15PM +0800, Hangyu Hua wrote:
If we send two TCA_FLOWER_KEY_ENC_OPTS_GENEVE packets and their total
size is 252 bytes(key->enc_opts.len = 252) then
key->enc_opts.len = opt->length = data_len / 4 = 0 when the third
TCA_FLOWER_KEY_ENC_OPTS_GENEVE packet enters fl_set_geneve_opt. This
bypasses the next bounds check and results in an out-of-bounds.

Fixes: 0a6e77784f49 ("net/sched: allow flower to match tunnel options")
Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx>

Hi Hangyu Hua,

Thanks. I think I see the problem too.
But I do wonder, is this more general than Geneve options?
That is, can this occur with any sequence of options, that
consume space in enc_opts (configured in fl_set_key()) that
in total are more than 256 bytes?

Hi Hangyu Hua,

Thank you for the patch. In addition to Simon's comment; I think the subject
headline should include net, i.e. [PATCH net]. Also could you please provide

My bad. I forgot this rule. It seems this won't be included in the final patch. Do i need to send a v2?

an example tc filter add dev... command to replicate the issue? (Just to make
it a bit easier to understand).

I use poc.c instead of commands to trigger this bug. If you want poc You
can check if there is an email named "Re: A possible LPE vulnerability in fl_set_geneve_opt" in your e-mail. I should have sent it to you and Simon while replying to security@xxxxxxxxxx.


net/sched/cls_flower.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
index e960a46b0520..a326fbfe4339 100644
--- a/net/sched/cls_flower.c
+++ b/net/sched/cls_flower.c
@@ -1153,6 +1153,9 @@ static int fl_set_geneve_opt(const struct nlattr *nla, struct fl_flow_key *key,
if (option_len > sizeof(struct geneve_opt))
data_len = option_len - sizeof(struct geneve_opt);
+ if (key->enc_opts.len > FLOW_DIS_TUN_OPTS_MAX - 4)
+ return -ERANGE;
opt = (struct geneve_opt *)&key->[key->enc_opts.len];
memset(opt, 0xff, option_len);
opt->length = data_len / 4;