[PATCH AUTOSEL 6.1 34/46] wifi: mac80211_hwsim: Prevent tsf from setting if beacon is disabled

[Sasha Levin <sashal@kernel.org>]

From: Edward Adam Davis <eadavis@qq.com>

[ Upstream commit c575f5374be7a5c4be4acb9fe6be3a4669d94674 ]

Setting tsf is meaningless if beacon is disabled, so check that beacon
is enabled before setting tsf.

Reported-by: syzbot+064815c6cd721082a52a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=064815c6cd721082a52a
Tested-by: syzbot+064815c6cd721082a52a@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Link: https://patch.msgid.link/tencent_3609AC2EFAAED68CA5A7E3C6D212D1C67806@qq.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

Perfect! Now I can see the exact issue. The function uses `do_div(delta,
bcn_int)` where `bcn_int` comes from `data->link_data[0].beacon_int`.
When beacons are disabled, this value could be 0, leading to a division
by zero error. **YES** This commit should be backported to stable kernel
trees. Here's my extensive analysis: ## Analysis of the Commit ### The
Bug The commit fixes a **division by zero vulnerability** in the
`mac80211_hwsim_set_tsf()` function. The issue occurs when: 1. **Beacons
are disabled** (`enable_beacon = false`) 2. **Beacon interval becomes
0** (as seen in line 2569: `link_data->beacon_int = 0;`) 3. **TSF is
still being set**, leading to `do_div(delta, bcn_int)` operations where
`bcn_int = 0` ### Code Analysis The problematic code was: ```c u32
bcn_int = data->link_data[0].beacon_int; // Could be 0 when beacons
disabled u64 delta = abs(tsf - now); // ... data->bcn_delta =
do_div(delta, bcn_int); // Division by zero! ``` The fix adds a safety
check: ```c conf = link_conf_dereference_protected(vif,
data->link_data[0].link_id); if (conf && !conf->enable_beacon) return;
// Exit early when beacons are disabled ``` ### Why This Should Be
Backported 1. **Critical Bug Fix**: This fixes a **division by zero
kernel bug** that could cause kernel panics or crashes. 2. **Security
Issue**: The commit references a **syzbot report**
(`syzbot+064815c6cd721082a52a@syzkaller.appspotmail.com`), indicating
this is a reproducible security issue found by automated fuzzing. 3.
**Small and Contained**: The fix is minimal - just 5 lines of code that
add a safety check. It follows the stable tree rule of being a small,
targeted fix. 4. **No Architectural Changes**: This doesn't introduce
new features or make architectural changes. It simply prevents an
invalid operation from occurring. 5. **Low Regression Risk**: The fix is
defensive programming - it only prevents the function from executing
when beacons are disabled, which makes logical sense since TSF
adjustment is meaningless without beacons. 6. **Driver-Specific**: This
affects the `mac80211_hwsim` virtual driver, which is commonly used for
testing and virtualization, making the fix important for testing
infrastructure. 7. **Logical Fix**: The commit message clearly states
"Setting tsf is meaningless if beacon is disabled" - this is a logical
improvement that prevents undefined behavior. ### Backport Suitability -
✅ **Bug fix**: Yes, fixes division by zero - ✅ **Small change**: Only 5
lines added - ✅ **Contained**: Limited to one function in one driver - ✅
**Low risk**: Defensive check, cannot cause regressions - ✅ **Security
relevant**: Prevents kernel crashes - ✅ **Clear benefit**: Prevents
undefined behavior This is exactly the type of commit that stable trees
are designed for - a small, targeted fix for a real bug that affects
system stability.

 drivers/net/wireless/mac80211_hwsim.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/wireless/mac80211_hwsim.c b/drivers/net/wireless/mac80211_hwsim.c
index abcd165a62cfe..80a2a668cfb9e 100644
--- a/drivers/net/wireless/mac80211_hwsim.c
+++ b/drivers/net/wireless/mac80211_hwsim.c
@@ -1091,6 +1091,11 @@ static void mac80211_hwsim_set_tsf(struct ieee80211_hw *hw,
 	/* MLD not supported here */
 	u32 bcn_int = data->link_data[0].beacon_int;
 	u64 delta = abs(tsf - now);
+	struct ieee80211_bss_conf *conf;
+
+	conf = link_conf_dereference_protected(vif, data->link_data[0].link_id);
+	if (conf && !conf->enable_beacon)
+		return;
 
 	/* adjust after beaconing with new timestamp at old TBTT */
 	if (tsf > now) {
-- 
2.39.5