[PATCH 6.0 0878/1073] net_sched: reject TCF_EM_SIMPLE case for complex ematch module

Greg Kroah-Hartman
2022-12-28T16:35:53Z

From: Cong Wang <cong.wang@bytedance.com>

[ Upstream commit 9cd3fd2054c3b3055163accbf2f31a4426f10317 ]

When TCF_EM_SIMPLE was introduced, it is supposed to be convenient
for ematch implementation:

https://lore.kernel.org/all/20050105110048.GO26856@postel.suug.ch/

"You don't have to, providing a 32bit data chunk without TCF_EM_SIMPLE
set will simply result in allocating & copy. It's an optimization,
nothing more."

So if an ematch module provides ops->datalen that means it wants a
complex data structure (saved in its em->data) instead of a simple u32
value. We should simply reject such a combination, otherwise this u32
could be misinterpreted as a pointer.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-and-tested-by: syzbot+4caeae4c7103813598ae@syzkaller.appspotmail.com
Reported-by: Jun Nie <jun.nie@linaro.org>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sched/ematch.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/net/sched/ematch.c b/net/sched/ematch.c
index 4ce681361851..5c1235e6076a 100644
--- a/net/sched/ematch.c
+++ b/net/sched/ematch.c
@@ -255,6 +255,8 @@ static int tcf_em_validate(struct tcf_proto *tp,
* the value carried.
*/
if (em_hdr->flags & TCF_EM_SIMPLE) {
+ if (em->ops->datalen > 0)
+ goto errout;
if (data_len < sizeof(u32))
goto errout;
em->data = *(u32 *) data;
--
2.35.1