-----Original Message-----
From: Dan Carpenter <redacted>
Sent: Tuesday, November 2, 2021 9:15 PM
To: Pkshih <pkshih@realtek.com>
Cc: Colin King <redacted>; Kalle Valo <redacted>; David S . Miller
[off-list ref]; Jakub Kicinski [off-list ref]; linux-wireless@vger.kernel.org;
netdev@vger.kernel.org; kernel-janitors@vger.kernel.org; linux-kernel@vger.kernel.org
Subject: Re: [PATCH][next] rtw89: Fix potential dereference of the null pointer sta

On Mon, Oct 18, 2021 at 03:35:28AM +0000, Pkshih wrote:

quoted

quoted

-----Original Message-----
From: Colin King <redacted>
Sent: Friday, October 15, 2021 11:46 PM
To: Kalle Valo <redacted>; David S . Miller <davem@davemloft.net>; Jakub Kicinski
[off-list ref]; Pkshih [off-list ref]; linux-wireless@vger.kernel.org;
netdev@vger.kernel.org
Cc: kernel-janitors@vger.kernel.org; linux-kernel@vger.kernel.org
Subject: [PATCH][next] rtw89: Fix potential dereference of the null pointer sta

From: Colin Ian King <redacted>

The pointer rtwsta is dereferencing pointer sta before sta is
being null checked, so there is a potential null pointer deference
issue that may occur. Fix this by only assigning rtwsta after sta
has been null checked. Add in a null pointer check on rtwsta before
dereferencing it too.

Fixes: e3ec7017f6a2 ("rtw89: add Realtek 802.11ax driver")
Addresses-Coverity: ("Dereference before null check")
Signed-off-by: Colin Ian King <redacted>
---
 drivers/net/wireless/realtek/rtw89/core.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw89/core.c

b/drivers/net/wireless/realtek/rtw89/core.c
index 06fb6e5b1b37..26f52a25f545 100644

--- a/drivers/net/wireless/realtek/rtw89/core.c
+++ b/drivers/net/wireless/realtek/rtw89/core.c

@@ -1534,9 +1534,14 @@ static bool rtw89_core_txq_agg_wait(struct rtw89_dev *rtwdev,
 {
 	struct rtw89_txq *rtwtxq = (struct rtw89_txq *)txq->drv_priv;
 	struct ieee80211_sta *sta = txq->sta;
-	struct rtw89_sta *rtwsta = (struct rtw89_sta *)sta->drv_priv;

'sta->drv_priv' is only a pointer, we don't really dereference the
data right here, so I think this is safe. More, compiler can optimize
this instruction that reorder it to the place just right before using.
So, it seems like a false alarm.

The warning is about "sta" not "sta->priv".  It's not a false positive.

I have heard discussions about compilers trying to work around these
bugs by re-ordering the code.  Is that an option in GCC?  It's not
something we should rely on, but I'm just curious if it exists in
released versions.

I say GCC does "reorder" the code, because the object codes of following
two codes are identical with default or -Os ccflags.
If I misuse the term, please correct me.

Code-1:
	struct rtw89_sta *rtwsta = (struct rtw89_sta *)sta->drv_priv;

	if (!sta)
		return false;

	if (rtwsta->max_agg_wait <= 0)
		return false;

Code-2:
	struct rtw89_sta *rtwsta;

	if (!sta)
		return false;

	rtwsta = (struct rtw89_sta *)sta->drv_priv;
	if (rtwsta->max_agg_wait <= 0)
		return false;


The code-1 is the original code Coverity and smatch warn use-before-check.
The code-2 can avoid this warning without doubt.

To be clear, I have sent a patch to fix this.

--
Ping-Ke