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Sat, 06 Dec 2025 09:33:51 -0800 (PST) Received: from dkarn-thinkpadp16vgen1.punetw6.csb ([2402:e280:3e0d:a45:3861:8b7f:6ae1:6229]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29daeaab1d6sm81026605ad.67.2025.12.06.09.33.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 06 Dec 2025 09:33:50 -0800 (PST) From: Deepakkumar Karn To: johannes@sipsolutions.net Cc: dkarn@redhat.com, linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org, shaul.triebitz@intel.com, syzbot+5bb5f06f99924ea0cf86@syzkaller.appspotmail.com Subject: Re: [PATCH] mac80211_hwsim: fix divide error in mac80211_hwsim_link_info_changed Date: Sat, 6 Dec 2025 23:03:45 +0530 Message-ID: <20251206173345.356068-1-dkarn@redhat.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <6cc422bb9525be529c6b0d2d25f9869ca41ec77d.camel@sipsolutions.net> References: <6cc422bb9525be529c6b0d2d25f9869ca41ec77d.camel@sipsolutions.net> Precedence: bulk X-Mailing-List: linux-wireless@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit > On Sat, 2025-12-06 at 04:33 +0530, Deepakkumar Karn wrote: > > On Fri, 05 Dec 2025 18:39:49 +0100, Johannes Berg wrote: > > > Seems like we should not let userspace do that, to protect all other > > > drivers too, not just hwsim. > > > > As suggested, we should provide a zero-value division check for other > > drivers as well. I will investigate other places where divide errors can > > occur due to edge cases. > What, no no. > > Please let me know if you meant something different. In the meantime, > > I will analyze other drivers for similar cases. > I did. My point is we shouldn't _have_ to check any drivers for this at > all, it's nonsense and higher layers (here cfg80211) should reject it. Thank you for your response Johannes. cfg80211 already have validation in cfg80211_validate_beacon_int(). The problem seems to occur in case of interface shutdown which calls ieee80211_do_stop() that makes beacon_int = 0 or set_tsf which causes divides by zero. What if we: 1. Handle off-channel operation: diff --git a/net/mac80211/offchannel.c b/net/mac80211/offchannel.c index ae82533e3c02..14a103d320e3 100644 --- a/net/mac80211/offchannel.c +++ b/net/mac80211/offchannel.c @@ -156,10 +156,12 @@ void ieee80211_offchannel_return(struct ieee80211_local *local) if (test_and_clear_bit(SDATA_STATE_OFFCHANNEL_BEACON_STOPPED, &sdata->state)) { - sdata->vif.bss_conf.enable_beacon = true; - ieee80211_link_info_change_notify( - sdata, &sdata->deflink, - BSS_CHANGED_BEACON_ENABLED); + if (sdata->vif.bss_conf.beacon_int) { + sdata->vif.bss_conf.enable_beacon = true; + ieee80211_link_info_change_notify( + sdata, &sdata->deflink, + BSS_CHANGED_BEACON_ENABLED); + } } } 2. Handle case where debugfs is written after shutdown or any race condition during disable beaconing: diff --git a/drivers/net/wireless/virtual/mac80211_hwsim.c b/drivers/net/wireless/virtual/mac80211_hwsim.c index 551f5eb4e747..8363cdd17a97 100644 --- a/drivers/net/wireless/virtual/mac80211_hwsim.c +++ b/drivers/net/wireless/virtual/mac80211_hwsim.c @@ -1242,7 +1242,7 @@ static void mac80211_hwsim_set_tsf(struct ieee80211_hw *hw, struct ieee80211_bss_conf *conf; conf = link_conf_dereference_protected(vif, data->link_data[0].link_id); - if (conf && !conf->enable_beacon) + if ((conf && !conf->enable_beacon) || !bcn_int) return; /* adjust after beaconing with new timestamp at old TBTT */ 3. As other drivers already have beacon_int 0 value validation, consider earlier patch along with above 2 points?