[PATCH 5.15 19/27] wifi: cfg80211: fix BSS refcounting bugs

Greg Kroah-Hartman
2022-10-13T18:15:01Z

From: Johannes Berg <johannes.berg@intel.com>

commit 0b7808818cb9df6680f98996b8e9a439fa7bcc2f upstream.

There are multiple refcounting bugs related to multi-BSSID:
- In bss_ref_get(), if the BSS has a hidden_beacon_bss, then
the bss pointer is overwritten before checking for the
transmitted BSS, which is clearly wrong. Fix this by using
the bss_from_pub() macro.

- In cfg80211_bss_update() we copy the transmitted_bss pointer
from tmp into new, but then if we release new, we'll unref
it erroneously. We already set the pointer and ref it, but
need to NULL it since it was copied from the tmp data.

- In cfg80211_inform_single_bss_data(), if adding to the non-
transmitted list fails, we unlink the BSS and yet still we
return it, but this results in returning an entry without
a reference. We shouldn't return it anyway if it was broken
enough to not get added there.

This fixes CVE-2022-42720.

Reported-by: Sönke Huster <shuster@seemoo.tu-darmstadt.de>
Tested-by: Sönke Huster <shuster@seemoo.tu-darmstadt.de>
Fixes: a3584f56de1c ("cfg80211: Properly track transmitting and non-transmitting BSS")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/wireless/scan.c | 27 ++++++++++++++-------------
1 file changed, 14 insertions(+), 13 deletions(-)

--- a/net/wireless/scan.c
+++ b/net/wireless/scan.c
@@ -143,18 +143,12 @@ static inline void bss_ref_get(struct cf
lockdep_assert_held(&rdev->bss_lock);

bss->refcount++;
- if (bss->pub.hidden_beacon_bss) {
- bss = container_of(bss->pub.hidden_beacon_bss,
- struct cfg80211_internal_bss,
- pub);
- bss->refcount++;
- }
- if (bss->pub.transmitted_bss) {
- bss = container_of(bss->pub.transmitted_bss,
- struct cfg80211_internal_bss,
- pub);
- bss->refcount++;
- }
+
+ if (bss->pub.hidden_beacon_bss)
+ bss_from_pub(bss->pub.hidden_beacon_bss)->refcount++;
+
+ if (bss->pub.transmitted_bss)
+ bss_from_pub(bss->pub.transmitted_bss)->refcount++;
}

static inline void bss_ref_put(struct cfg80211_registered_device *rdev,
@@ -1743,6 +1737,8 @@ cfg80211_bss_update(struct cfg80211_regi
new->refcount = 1;
INIT_LIST_HEAD(&new->hidden_list);
INIT_LIST_HEAD(&new->pub.nontrans_list);
+ /* we'll set this later if it was non-NULL */
+ new->pub.transmitted_bss = NULL;

if (rcu_access_pointer(tmp->pub.proberesp_ies)) {
hidden = rb_find_bss(rdev, tmp, BSS_CMP_HIDE_ZLEN);
@@ -1983,10 +1979,15 @@ cfg80211_inform_single_bss_data(struct w
spin_lock_bh(&rdev->bss_lock);
if (cfg80211_add_nontrans_list(non_tx_data->tx_bss,
&res->pub)) {
- if (__cfg80211_unlink_bss(rdev, res))
+ if (__cfg80211_unlink_bss(rdev, res)) {
rdev->bss_generation++;
+ res = NULL;
+ }
}
spin_unlock_bh(&rdev->bss_lock);
+
+ if (!res)
+ return NULL;
}

trace_cfg80211_return_bss(&res->pub);