Re: [Patch net] cls_flower: call nla_ok() before nla_next()

On Wed, Jan 13, 2021 at 1:43 AM Cong Wang [off-list ref] wrote:

On Tue, Jan 12, 2021 at 3:52 AM Xin Long [off-list ref] wrote:

quoted

On Tue, Jan 12, 2021 at 10:56 AM Cong Wang [off-list ref] wrote:

quoted

From: Cong Wang <redacted>

fl_set_enc_opt() simply checks if there are still bytes left to parse,
but this is not sufficent as syzbot seems to be able to generate
malformatted netlink messages. nla_ok() is more strict so should be
used to validate the next nlattr here.

And nla_validate_nested_deprecated() has less strict check too, it is
probably too late to switch to the strict version, but we can just
call nla_ok() too after it.

Reported-and-tested-by: syzbot+2624e3778b18fc497c92@syzkaller.appspotmail.com
Fixes: 0a6e77784f49 ("net/sched: allow flower to match tunnel options")
Fixes: 79b1011cb33d ("net: sched: allow flower to match erspan options")
Cc: Pieter Jansen van Vuuren <redacted>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Xin Long <lucien.xin@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <redacted>
---
 net/sched/cls_flower.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
index 1319986693fc..e265c443536e 100644
--- a/net/sched/cls_flower.c
+++ b/net/sched/cls_flower.c

@@ -1272,6 +1272,8 @@ static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,

                nla_opt_msk = nla_data(tb[TCA_FLOWER_KEY_ENC_OPTS_MASK]);
                msk_depth = nla_len(tb[TCA_FLOWER_KEY_ENC_OPTS_MASK]);
+               if (!nla_ok(nla_opt_msk, msk_depth))
+                       return -EINVAL;
        }

I think it's better to also add  NL_SET_ERR_MSG(extack, xxxx);
for this error return, like all the other places in this function.

I think ext message is primarily for end users who usually can not
generate malformat netlink messages.

On the other hand, the nla_validate_nested_deprecated() right above
the quoted code does not set ext message either.

nla_validate_nested_deprecated(..., extack), it's already done inside
when returns error, no?