Re: [PATCH v2][next] wifi: wil6210: Annotate a couple of structs with __counted_by()

[Gustavo A. R. Silva]

On 3/27/24 12:26, Jeff Johnson wrote:
> On 3/27/2024 10:43 AM, Gustavo A. R. Silva wrote:
> > Prepare for the coming implementation by GCC and Clang of the __counted_by
> > attribute. Flexible array members annotated with __counted_by can have
> > their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> > array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> > functions).
> >
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> > ---
> > Changes in v2:
> >   - Annotate one more struct.
> >   - Update Subject line.
> >
> > v1:
> >   - Link: https://lore.kernel.org/linux-hardening/ZgODZOB4fOBvKl7R@neat/
> >
> >   drivers/net/wireless/ath/wil6210/wmi.h | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/wireless/ath/wil6210/wmi.h b/drivers/net/wireless/ath/wil6210/wmi.h
> > index 71bf2ae27a98..38f64524019e 100644
> > --- a/drivers/net/wireless/ath/wil6210/wmi.h
> > +++ b/drivers/net/wireless/ath/wil6210/wmi.h
> > @@ -474,7 +474,7 @@ struct wmi_start_scan_cmd {
> >   	struct {
> >   		u8 channel;
> >   		u8 reserved;
> > -	} channel_list[];
> > +	} channel_list[] __counted_by(num_channels);
> >   } __packed;
>
> does the compiler handle the actual logic where it is modifying num_channels
> concurrently with writing into the array? i.e. this will be writing into
> channel_list[0] when num_channels is 0:

I'm actually about to send this patch:

diff --git a/drivers/net/wireless/ath/wil6210/cfg80211.c b/drivers/net/wireless/ath/wil6210/cfg80211.c
index dbe4b3478f03..836b49954171 100644
--- a/drivers/net/wireless/ath/wil6210/cfg80211.c
+++ b/drivers/net/wireless/ath/wil6210/cfg80211.c
@@ -892,10 +892,8 @@ static int wil_cfg80211_scan(struct wiphy *wiphy,
        struct wil6210_priv *wil = wiphy_to_wil(wiphy);
        struct wireless_dev *wdev = request->wdev;
        struct wil6210_vif *vif = wdev_to_vif(wil, wdev);
-       struct {
-               struct wmi_start_scan_cmd cmd;
-               u16 chnl[4];
-       } __packed cmd;
+       DEFINE_FLEX(struct wmi_start_scan_cmd, cmd,
+                   channel_list, num_channels, 4);
        uint i, n;
        int rc;

@@ -977,9 +975,9 @@ static int wil_cfg80211_scan(struct wiphy *wiphy,
        vif->scan_request = request;
        mod_timer(&vif->scan_timer, jiffies + WIL6210_SCAN_TO);

-       memset(&cmd, 0, sizeof(cmd));
-       cmd.cmd.scan_type = WMI_ACTIVE_SCAN;
-       cmd.cmd.num_channels = 0;
+       memset(cmd, 0, sizeof(*cmd));
+       cmd->scan_type = WMI_ACTIVE_SCAN;
+       cmd->num_channels = 0;
        n = min(request->n_channels, 4U);
        for (i = 0; i < n; i++) {
                int ch = request->channels[i]->hw_value;
@@ -991,7 +989,8 @@ static int wil_cfg80211_scan(struct wiphy *wiphy,
                        continue;
                }
                /* 0-based channel indexes */
-               cmd.cmd.channel_list[cmd.cmd.num_channels++].channel = ch - 1;
+               cmd->num_channels++;
+               cmd->channel_list[cmd->num_channels - 1].channel = ch - 1;
                wil_dbg_misc(wil, "Scan for ch %d  : %d MHz\n", ch,
                             request->channels[i]->center_freq);
        }
@@ -1007,16 +1006,15 @@ static int wil_cfg80211_scan(struct wiphy *wiphy,
        if (rc)
                goto out_restore;

-       if (wil->discovery_mode && cmd.cmd.scan_type == WMI_ACTIVE_SCAN) {
-               cmd.cmd.discovery_mode = 1;
+       if (wil->discovery_mode && cmd->scan_type == WMI_ACTIVE_SCAN) {
+               cmd->discovery_mode = 1;
                wil_dbg_misc(wil, "active scan with discovery_mode=1\n");
        }

        if (vif->mid == 0)
                wil->radio_wdev = wdev;
        rc = wmi_send(wil, WMI_START_SCAN_CMDID, vif->mid,
-                     &cmd, sizeof(cmd.cmd) +
-                     cmd.cmd.num_channels * sizeof(cmd.cmd.channel_list[0]));
+                     cmd, struct_size(cmd, channel_list, cmd->num_channels));

 out_restore:
        if (rc) {



--
Gustavo

> 		cmd.cmd.channel_list[cmd.cmd.num_channels++].channel = ch - 1;
>
> if that will cause a bounds check failure then suggest you change the logic so
> that it updates num_channels before writing into channel_list
>
> >   
> >   #define WMI_MAX_PNO_SSID_NUM	(16)
> > @@ -3320,7 +3320,7 @@ struct wmi_set_link_monitor_cmd {
> >   	u8 rssi_hyst;
> >   	u8 reserved[12];
> >   	u8 rssi_thresholds_list_size;
> > -	s8 rssi_thresholds_list[];
> > +	s8 rssi_thresholds_list[] __counted_by(rssi_thresholds_list_size);
> >   } __packed;
>
> this looks ok to me, although I think there is another issue associated with
> this, namely the way the code populates the rssi_thresholds_list is by
> defining a separate anonymous struct:
> 	struct {
> 		struct wmi_set_link_monitor_cmd cmd;
> 		s8 rssi_thold;
> 	} __packed cmd = {
> 		.cmd = {
> 			.rssi_hyst = rssi_hyst,
> 			.rssi_thresholds_list_size = 1,
> 		},
> 		.rssi_thold = rssi_thold,
> 	};
>
> I would expect gcc and clang to both complain about that s8 rssi_thold comes
> after a flexible array (even though its purpose is to be the value of
> rssi_thresholds_list[0])
>
> /jeff
>
>
> >   
> >   /* wmi_link_monitor_event_type */