When we are not connected to a channel, sending channel "switch" announcement doesn't make any sense.

The BSS list is empty in that case. This causes the for loop in cfg80211_get_bss() to be bypassed, so the function returns NULL (check line 1424 of net/wireless/scan.c), causing the WARN_ON() in ieee80211_ibss_csa_beacon() to get triggered (check line 500 of net/mac80211/ibss.c), which was consequently reported on the syzkaller dashboard.

Thus, check if we have an existing connection before generating the CSA beacon in ieee80211_ibss_finish_csa().

Fixes: cd7760e62c2a ("mac80211: add support for CSA in IBSS mode") Bug report: https://syzkaller.appspot.com/bug?id=05603ef4ae8926761b678d2939a3b2ad28ab9ca... Reported-by: syzbot+b6c9fe29aefe68e4ad34@syzkaller.appspotmail.com Cc: stable@vger.kernel.org

Signed-off-by: Siddh Raman Pant code@siddh.me --- The fixes commit is old, and syzkaller shows the problem exists for 4.19 and 4.14 as well, so CC'd stable list.

net/mac80211/ibss.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/net/mac80211/ibss.c b/net/mac80211/ibss.c index d56890e3fabb..9b283bbc7bb4 100644 --- a/net/mac80211/ibss.c +++ b/net/mac80211/ibss.c @@ -530,6 +530,10 @@ int ieee80211_ibss_finish_csa(struct ieee80211_sub_if_data *sdata)

sdata_assert_lock(sdata);

+ /* When not connected/joined, sending CSA doesn't make sense. */ + if (ifibss->state != IEEE80211_IBSS_MLME_JOINED) + return -ENOLINK; + /* update cfg80211 bss information with the new channel */ if (!is_zero_ether_addr(ifibss->bssid)) { cbss = cfg80211_get_bss(sdata->local->hw.wiphy,