[syzbot] [wireless?] divide error in mac80211_hwsim_set_tsf

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0af2f6be1b42 Linux 6.15-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1741cc04580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d444e5269179368a
dashboard link: https://syzkaller.appspot.com/bug?extid=064815c6cd721082a52a
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=140f9070580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8909dc8a51ee/disk-0af2f6be.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e216afa338a8/vmlinux-0af2f6be.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4d21115804e3/bzImage-0af2f6be.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+064815...@syzkaller.appspotmail.com

Oops: divide error: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 1148 Comm: kworker/u8:6 Not tainted 6.15.0-rc1-syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Workqueue: events_unbound cfg80211_wiphy_work
RIP: 0010:mac80211_hwsim_set_tsf+0x139/0x170 drivers/net/wireless/virtual/mac80211_hwsim.c:1239
Code: 48 89 9d 30 3f 00 00 4c 89 b5 28 3f 00 00 5b 5d 41 5c 41 5d 41 5e 41 5f c3 cc cc cc cc e8 9f cf c4 fa 45 89 ff 4c 89 e8 31 d2 <49> f7 f7 4d 29 ee 48 89 d3 48 f7 db eb a5 e8 54 40 29 fb e9 e7 fe
RSP: 0018:ffffc90003ff7ad8 EFLAGS: 00010246
RAX: 00063249cd8022f2 RBX: 00063249cd8022f3 RCX: ffffffff86f66d11
RDX: 0000000000000000 RSI: ffffffff86f66d71 RDI: 0000000000000006
RBP: ffff8880236830a0 R08: 0000000000000006 R09: 0000000000000001
R10: 00063249cd8022f3 R11: 0000000000000000 R12: 0000000000000001
R13: 00063249cd8022f2 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881249b9000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7019ad56c0 CR3: 00000000336ea000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
drv_set_tsf+0x223/0x590 net/mac80211/driver-ops.c:277
ieee80211_if_parse_tsf+0x2c8/0x560 net/mac80211/debugfs_netdev.c:701
wiphy_locked_debugfs_write_work+0xe3/0x1c0 net/wireless/debugfs.c:215
cfg80211_wiphy_work+0x3dc/0x550 net/wireless/core.c:435
process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
process_scheduled_works kernel/workqueue.c:3319 [inline]
worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
kthread+0x3c2/0x780 kernel/kthread.c:464
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:mac80211_hwsim_set_tsf+0x139/0x170 drivers/net/wireless/virtual/mac80211_hwsim.c:1239
Code: 48 89 9d 30 3f 00 00 4c 89 b5 28 3f 00 00 5b 5d 41 5c 41 5d 41 5e 41 5f c3 cc cc cc cc e8 9f cf c4 fa 45 89 ff 4c 89 e8 31 d2 <49> f7 f7 4d 29 ee 48 89 d3 48 f7 db eb a5 e8 54 40 29 fb e9 e7 fe
RSP: 0018:ffffc90003ff7ad8 EFLAGS: 00010246
RAX: 00063249cd8022f2 RBX: 00063249cd8022f3 RCX: ffffffff86f66d11
RDX: 0000000000000000 RSI: ffffffff86f66d71 RDI: 0000000000000006
RBP: ffff8880236830a0 R08: 0000000000000006 R09: 0000000000000001
R10: 00063249cd8022f3 R11: 0000000000000000 R12: 0000000000000001
R13: 00063249cd8022f2 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881249b9000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7019ad56c0 CR3: 0000000034a5e000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 48 89 9d 30 3f 00 00 mov %rbx,0x3f30(%rbp)
7: 4c 89 b5 28 3f 00 00 mov %r14,0x3f28(%rbp)
e: 5b pop %rbx
f: 5d pop %rbp
10: 41 5c pop %r12
12: 41 5d pop %r13
14: 41 5e pop %r14
16: 41 5f pop %r15
18: c3 ret
19: cc int3
1a: cc int3
1b: cc int3
1c: cc int3
1d: e8 9f cf c4 fa call 0xfac4cfc1
22: 45 89 ff mov %r15d,%r15d
25: 4c 89 e8 mov %r13,%rax
28: 31 d2 xor %edx,%edx
* 2a: 49 f7 f7 div %r15 <-- trapping instruction
2d: 4d 29 ee sub %r13,%r14
30: 48 89 d3 mov %rdx,%rbx
33: 48 f7 db neg %rbx
36: eb a5 jmp 0xffffffdd
38: e8 54 40 29 fb call 0xfb294091
3d: e9 .byte 0xe9
3e: e7 fe out %eax,$0xfe


---
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[Edward Adam Davis]

#syz test

diff --git a/drivers/net/wireless/virtual/mac80211_hwsim.c b/drivers/net/wireless/virtual/mac80211_hwsim.c
index cf3e976471c6..cd9e89aebb83 100644
--- a/drivers/net/wireless/virtual/mac80211_hwsim.c
+++ b/drivers/net/wireless/virtual/mac80211_hwsim.c
@@ -1226,6 +1226,11 @@ static void mac80211_hwsim_set_tsf(struct ieee80211_hw *hw,
{
struct mac80211_hwsim_data *data = hw->priv;
u64 now = mac80211_hwsim_get_tsf(hw, vif);
+ struct ieee80211_bss_conf *conf = link_conf_dereference_protected(vif,
+ data->link_data[0].link_id);
+
+ if (conf && !conf->enable_beacon)
+ return;
/* MLD not supported here */
u32 bcn_int = data->link_data[0].beacon_int;
u64 delta = abs(tsf - now);

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
unregister_netdevice: waiting for DEV to become free

unregister_netdevice: waiting for batadv0 to become free. Usage count = 3


Tested on:

commit: 7cdabafc Merge tag 'trace-v6.15-rc1' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11f3d398580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7a4e108575159039

dashboard link: https://syzkaller.appspot.com/bug?extid=064815c6cd721082a52a
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=15e49870580000

[Edward Adam Davis]

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

Reported-by: syzbot+064815...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=064815c6cd721082a52a
Tested-by: syzbot+064815...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
drivers/net/wireless/virtual/mac80211_hwsim.c | 5 +++++
1 file changed, 5 insertions(+)

--
2.43.0

[Johannes Berg]

On Sun, 2025-04-13 at 14:11 +0800, Edward Adam Davis wrote:
>
> --- a/drivers/net/wireless/virtual/mac80211_hwsim.c
> +++ b/drivers/net/wireless/virtual/mac80211_hwsim.c
> @@ -1226,6 +1226,11 @@ static void mac80211_hwsim_set_tsf(struct ieee80211_hw *hw,
> {
> struct mac80211_hwsim_data *data = hw->priv;
> u64 now = mac80211_hwsim_get_tsf(hw, vif);
> + struct ieee80211_bss_conf *conf = link_conf_dereference_protected(vif,
> + data->link_data[0].link_id);
> +
> + if (conf && !conf->enable_beacon)
> + return;
> /* MLD not supported here */
> u32 bcn_int = data->link_data[0].beacon_int;
> u64 delta = abs(tsf - now);

Please keep kernel coding style - the line break there is awful (but
with "conf = ..." on a line by itself it can be just one line), and you
shouldn't have code before variable declarations.

The comment should probably also move because it's relevant for your new
[0] as well.

johannes

[Edward Adam Davis]

On Wed, 23 Apr 2025 14:53:53 +0200, Johannes Berg wrote:
> > --- a/drivers/net/wireless/virtual/mac80211_hwsim.c
> > +++ b/drivers/net/wireless/virtual/mac80211_hwsim.c
> > @@ -1226,6 +1226,11 @@ static void mac80211_hwsim_set_tsf(struct ieee80211_hw *hw,
> > {
> > struct mac80211_hwsim_data *data = hw->priv;
> > u64 now = mac80211_hwsim_get_tsf(hw, vif);
> > + struct ieee80211_bss_conf *conf = link_conf_dereference_protected(vif,
> > + data->link_data[0].link_id);
> > +
> > + if (conf && !conf->enable_beacon)
> > + return;
> > /* MLD not supported here */
> > u32 bcn_int = data->link_data[0].beacon_int;
> > u64 delta = abs(tsf - now);
>
> Please keep kernel coding style - the line break there is awful (but
> with "conf = ..." on a line by itself it can be just one line), and you
> shouldn't have code before variable declarations.

like this?
diff --git a/drivers/net/wireless/virtual/mac80211_hwsim.c b/drivers/net/wireless/virtual/mac80211_hwsim.c
index cf3e976471c6..6ca5d9d0fe53 100644
--- a/drivers/net/wireless/virtual/mac80211_hwsim.c
+++ b/drivers/net/wireless/virtual/mac80211_hwsim.c
@@ -1229,6 +1229,11 @@ 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) {

>
> The comment should probably also move because it's relevant for your new
> [0] as well.

I don't understand what you mean.

Edward

[Johannes Berg]

On Wed, 2025-04-23 at 21:56 +0800, Edward Adam Davis wrote:
> On Wed, 23 Apr 2025 14:53:53 +0200, Johannes Berg wrote:
> > > --- a/drivers/net/wireless/virtual/mac80211_hwsim.c
> > > +++ b/drivers/net/wireless/virtual/mac80211_hwsim.c
> > > @@ -1226,6 +1226,11 @@ static void mac80211_hwsim_set_tsf(struct ieee80211_hw *hw,
> > > {
> > > struct mac80211_hwsim_data *data = hw->priv;
> > > u64 now = mac80211_hwsim_get_tsf(hw, vif);
> > > + struct ieee80211_bss_conf *conf = link_conf_dereference_protected(vif,
> > > + data->link_data[0].link_id);
> > > +
> > > + if (conf && !conf->enable_beacon)
> > > + return;
> > > /* MLD not supported here */
> > > u32 bcn_int = data->link_data[0].beacon_int;
> > > u64 delta = abs(tsf - now);
> >
> > Please keep kernel coding style - the line break there is awful (but
> > with "conf = ..." on a line by itself it can be just one line), and you
> > shouldn't have code before variable declarations.
> like this?

Looks good I guess, not sure you wanted bcn_int/delta to be calculated
before or after.

> > The comment should probably also move because it's relevant for your new
> > [0] as well.
> I don't understand what you mean.

The "/* MLD not supported here */" comment refers to the [0] - it
explains why the [0] (rather than link id) is OK. So it also applies to
your [0], if you're going to put it before the comment then IMHO it
makes sense to move the comment. With what you did now the comment is
still earlier though, of course.

johannes

[Edward Adam Davis]

On Wed, 23 Apr 2025 16:04:04 +0200, Johannes Berg wrote:
> On Wed, 2025-04-23 at 21:56 +0800, Edward Adam Davis wrote:
> > On Wed, 23 Apr 2025 14:53:53 +0200, Johannes Berg wrote:
> > > > --- a/drivers/net/wireless/virtual/mac80211_hwsim.c
> > > > +++ b/drivers/net/wireless/virtual/mac80211_hwsim.c
> > > > @@ -1226,6 +1226,11 @@ static void mac80211_hwsim_set_tsf(struct ieee80211_hw *hw,
> > > > {
> > > > struct mac80211_hwsim_data *data = hw->priv;
> > > > u64 now = mac80211_hwsim_get_tsf(hw, vif);
> > > > + struct ieee80211_bss_conf *conf = link_conf_dereference_protected(vif,
> > > > + data->link_data[0].link_id);
> > > > +
> > > > + if (conf && !conf->enable_beacon)
> > > > + return;
> > > > /* MLD not supported here */
> > > > u32 bcn_int = data->link_data[0].beacon_int;
> > > > u64 delta = abs(tsf - now);
> > >
> > > Please keep kernel coding style - the line break there is awful (but
> > > with "conf = ..." on a line by itself it can be just one line), and you
> > > shouldn't have code before variable declarations.
> > like this?
>
> Looks good I guess, not sure you wanted bcn_int/delta to be calculated
> before or after.

It will be all right.
I will send V2 patch.

>
> > > The comment should probably also move because it's relevant for your new
> > > [0] as well.
> > I don't understand what you mean.
>
> The "/* MLD not supported here */" comment refers to the [0] - it
> explains why the [0] (rather than link id) is OK. So it also applies to
> your [0], if you're going to put it before the comment then IMHO it
> makes sense to move the comment. With what you did now the comment is
> still earlier though, of course.

Oh, Got it.

Edward

[Edward Adam Davis]

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

Reported-by: syzbot+064815...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=064815c6cd721082a52a
Tested-by: syzbot+064815...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---

V1 -> V2: Move initialization and judgment to after delta.

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

diff --git a/drivers/net/wireless/virtual/mac80211_hwsim.c b/drivers/net/wireless/virtual/mac80211_hwsim.c
index cf3e976471c6..6ca5d9d0fe53 100644

--- a/drivers/net/wireless/virtual/mac80211_hwsim.c
+++ b/drivers/net/wireless/virtual/mac80211_hwsim.c
@@ -1229,6 +1229,11 @@ 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) {

--
2.43.0