2021-06-10 16:21:33

by Anirudh Rayabharam

Subject: [PATCH] mac80211_hwsim: correctly handle zero length frames

syzbot, using KMSAN, has reported an uninit-value access in
hwsim_cloned_frame_received_nl(). This is happening because frame_data_len
is 0. The code doesn't detect this case and blindly tries to read the
frame's header.

Fix this by bailing out in case frame_data_len is 0.

Reported-by: [email protected]
Tested-by: [email protected]
Signed-off-by: Anirudh Rayabharam <[email protected]>
---
drivers/net/wireless/mac80211_hwsim.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wireless/mac80211_hwsim.c b/drivers/net/wireless/mac80211_hwsim.c
index 51ce767eaf88..ccfe40313109 100644
--- a/drivers/net/wireless/mac80211_hwsim.c
+++ b/drivers/net/wireless/mac80211_hwsim.c
@@ -3649,7 +3649,7 @@ static int hwsim_cloned_frame_received_nl(struct sk_buff *skb_2,
if (skb == NULL)
goto err;

- if (frame_data_len > IEEE80211_MAX_DATA_LEN)
+ if (frame_data_len == 0 || frame_data_len > IEEE80211_MAX_DATA_LEN)
goto err;

/* Copy the data */
--
2.26.2

2021-06-23 07:27:15

by Anirudh Rayabharam

Subject: Re: [PATCH] mac80211_hwsim: correctly handle zero length frames

On Fri, Jun 18, 2021 at 11:36:16AM +0200, Johannes Berg wrote:
> On Thu, 2021-06-10 at 21:49 +0530, Anirudh Rayabharam wrote:
> > syzbot, using KMSAN, has reported an uninit-value access in
> > hwsim_cloned_frame_received_nl(). This is happening because frame_data_len
> > is 0. The code doesn't detect this case and blindly tries to read the
> > frame's header.
> >
> > Fix this by bailing out in case frame_data_len is 0.
>
> This really seems quite pointless - you should bail out if the frame is
> too short for what we need to do, not just when it's 0.

That makes sense. Do you happen to know what the min length of a valid
frame is? There doesn't seem to be constant defined for that already.

- Anirudh

>
> johannes
>