Re: [PATCH v2] net: mac80211: Add NULL checks for sta->sdata

From: Jia-Ju Bai
Date: Tue Apr 04 2023 - 05:58:38 EST

Hi Simon,

Thanks for your reply, and sorry for the delay.

On 2023/3/26 23:05, Simon Horman wrote:
On Tue, Mar 21, 2023 at 05:31:22PM +0800, Jia-Ju Bai wrote:
In a previous commit 69403bad97aa ("wifi: mac80211: sdata can be NULL
during AMPDU start"), sta->sdata can be NULL, and thus it should be
checked before being used.

However, in the same call stack, sta->sdata is also used in the
following functions:

ieee80211_ba_session_work()
___ieee80211_stop_rx_ba_session(sta)
ht_dbg(sta->sdata, ...); -> No check
sdata_info(sta->sdata, ...); -> No check
ieee80211_send_delba(sta->sdata, ...) -> No check
___ieee80211_start_rx_ba_session(sta)
ht_dbg(sta->sdata, ...); -> No check
ht_dbg_ratelimited(sta->sdata, ...); -> No check
ieee80211_tx_ba_session_handle_start(sta)
sdata = sta->sdata; if (!sdata) -> Add check by previous commit
___ieee80211_stop_tx_ba_session(sdata)
ht_dbg(sta->sdata, ...); -> No check
ieee80211_start_tx_ba_cb(sdata)
sdata = sta->sdata; local = sdata->local -> No check
ieee80211_stop_tx_ba_cb(sdata)
ht_dbg(sta->sdata, ...); -> No check

Thus, to avoid possible null-pointer dereferences, the related checks
should be added.

These bugs are reported by a static analysis tool implemented by myself,
and they are found by extending a known bug fixed in the previous commit.
Thus, they could be theoretical bugs.

Signed-off-by: Jia-Ju Bai <baijiaju@xxxxxxxxxxx>
---
v2:
* Fix an error reported by checkpatch.pl, and make the bug finding
process more clear in the description. Thanks for Simon's advice.
---
net/mac80211/agg-rx.c | 68 ++++++++++++++++++++++++++-----------------
net/mac80211/agg-tx.c | 16 ++++++++--
2 files changed, 55 insertions(+), 29 deletions(-)

diff --git a/net/mac80211/agg-rx.c b/net/mac80211/agg-rx.c
index c6fa53230450..6616970785a2 100644
--- a/net/mac80211/agg-rx.c
+++ b/net/mac80211/agg-rx.c
@@ -80,19 +80,21 @@ void ___ieee80211_stop_rx_ba_session(struct sta_info *sta, u16 tid,
RCU_INIT_POINTER(sta->ampdu_mlme.tid_rx[tid], NULL);
__clear_bit(tid, sta->ampdu_mlme.agg_session_valid);
- ht_dbg(sta->sdata,
- "Rx BA session stop requested for %pM tid %u %s reason: %d\n", > - sta->sta.addr, tid,
- initiator == WLAN_BACK_RECIPIENT ? "recipient" : "initiator",
- (int)reason);
+ if (sta->sdata) {
+ ht_dbg(sta->sdata,
+ "Rx BA session stop requested for %pM tid %u %s reason: %d\n",
+ sta->sta.addr, tid,
+ initiator == WLAN_BACK_RECIPIENT ? "recipient" : "initiator",
+ (int)reason);
+ }
The first line of the body of ___ieee80211_stop_rx_ba_session() is:

struct ieee80211_local *local = sta->sdata->local;

So a NULL pointer dereference will have occurred before
the checks this change adds to that function.

I checked the source code again (including the latest version 6.3-rc5).
The first line of the body of ___ieee80211_stop_rx_ba_session() is:

    struct ieee80211_local *local = sta->local;

Thus, there is no dereference of sta->sdata.

In a different function, namely ___ieee80211_start_rx_ba_session(), the first line is:

    struct ieee80211_local *local = sta->sdata->local;

Thus, there should be a NULL check for sta->sdata in this function.
I will add this in my patch v3.



- if (drv_ampdu_action(local, sta->sdata, &params))
+ if (sta->sdata && drv_ampdu_action(local, sta->sdata, &params))
sdata_info(sta->sdata,
"HW problem - can not stop rx aggregation for %pM tid %d\n",
sta->sta.addr, tid);
...

diff --git a/net/mac80211/agg-tx.c b/net/mac80211/agg-tx.c
index f9514bacbd4a..03b31b6e7ac7 100644
--- a/net/mac80211/agg-tx.c
+++ b/net/mac80211/agg-tx.c
@@ -368,8 +368,10 @@ int ___ieee80211_stop_tx_ba_session(struct sta_info *sta, u16 tid,
spin_unlock_bh(&sta->lock);
- ht_dbg(sta->sdata, "Tx BA session stop requested for %pM tid %u\n",
- sta->sta.addr, tid);
+ if (sta->sdata) {
+ ht_dbg(sta->sdata, "Tx BA session stop requested for %pM tid %u\n",
+ sta->sta.addr, tid);
+ }
This seems clean :)

del_timer_sync(&tid_tx->addba_resp_timer);
del_timer_sync(&tid_tx->session_timer);
@@ -776,7 +778,12 @@ void ieee80211_start_tx_ba_cb(struct sta_info *sta, int tid,
struct tid_ampdu_tx *tid_tx)
{
struct ieee80211_sub_if_data *sdata = sta->sdata;
- struct ieee80211_local *local = sdata->local;
+ struct ieee80211_local *local;
+
+ if (!sdata)
+ return;
I'm not sure that silently ignoring non-existent sdata is the right approach.
Perhaps a WARN_ON or WARN_ONCE is appropriate?

Okay, I will use WARN_ON  in my patch v3.


+
+ local = sdata->local;
if (WARN_ON(test_and_set_bit(HT_AGG_STATE_DRV_READY, &tid_tx->state)))
return;
@@ -902,6 +909,9 @@ void ieee80211_stop_tx_ba_cb(struct sta_info *sta, int tid,
bool send_delba = false;
bool start_txq = false;
+ if (!sdata)
+ return;
+
Ditto.

Okay, I will use WARN_ON  in my patch v3.


ht_dbg(sdata, "Stopping Tx BA session for %pM tid %d\n",
sta->sta.addr, tid);


Best wishes,
Jia-Ju Bai