[PATCH net] mISDN: annotate data-race around dev->work

[Eric Dumazet]

dev->work can re read locklessly in mISDN_read()
and mISDN_poll(). Add READ_ONCE()/WRITE_ONCE() annotations.

BUG: KCSAN: data-race in mISDN_ioctl / mISDN_read

write to 0xffff88812d848280 of 4 bytes by task 10864 on cpu 1:
misdn_add_timer drivers/isdn/mISDN/timerdev.c:175 [inline]
mISDN_ioctl+0x2fb/0x550 drivers/isdn/mISDN/timerdev.c:233
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88812d848280 of 4 bytes by task 10857 on cpu 0:
mISDN_read+0x1f2/0x470 drivers/isdn/mISDN/timerdev.c:112
do_loop_readv_writev fs/read_write.c:847 [inline]
vfs_readv+0x3fb/0x690 fs/read_write.c:1020
do_readv+0xe7/0x210 fs/read_write.c:1080
__do_sys_readv fs/read_write.c:1165 [inline]
__se_sys_readv fs/read_write.c:1162 [inline]
__x64_sys_readv+0x45/0x50 fs/read_write.c:1162
x64_sys_call+0x2831/0x3000 arch/x86/include/generated/asm/syscalls_64.h:20
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000 -> 0x00000001

Fixes: 1b2b03f8e514 ("Add mISDN core files")
Reported-by: syzbot <syzk...@googlegroups.com>
Signed-off-by: Eric Dumazet <edum...@google.com>
---
drivers/isdn/mISDN/timerdev.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/isdn/mISDN/timerdev.c b/drivers/isdn/mISDN/timerdev.c
index df98144a953946df0fc8669ae3e446d043b98155..33521c328a827311f0bf02b82e99bfd635ee4ec6 100644
--- a/drivers/isdn/mISDN/timerdev.c
+++ b/drivers/isdn/mISDN/timerdev.c
@@ -109,14 +109,14 @@ mISDN_read(struct file *filep, char __user *buf, size_t count, loff_t *off)
spin_unlock_irq(&dev->lock);
if (filep->f_flags & O_NONBLOCK)
return -EAGAIN;
- wait_event_interruptible(dev->wait, (dev->work ||
+ wait_event_interruptible(dev->wait, (READ_ONCE(dev->work) ||
!list_empty(list)));
if (signal_pending(current))
return -ERESTARTSYS;
spin_lock_irq(&dev->lock);
}
if (dev->work)
- dev->work = 0;
+ WRITE_ONCE(dev->work, 0);
if (!list_empty(list)) {
timer = list_first_entry(list, struct mISDNtimer, list);
list_del(&timer->list);
@@ -141,13 +141,16 @@ mISDN_poll(struct file *filep, poll_table *wait)
if (*debug & DEBUG_TIMER)
printk(KERN_DEBUG "%s(%p, %p)\n", __func__, filep, wait);
if (dev) {
+ u32 work;
+
poll_wait(filep, &dev->wait, wait);
mask = 0;
- if (dev->work || !list_empty(&dev->expired))
+ work = READ_ONCE(dev->work);
+ if (work || !list_empty(&dev->expired))
mask |= (EPOLLIN | EPOLLRDNORM);
if (*debug & DEBUG_TIMER)
printk(KERN_DEBUG "%s work(%d) empty(%d)\n", __func__,
- dev->work, list_empty(&dev->expired));
+ work, list_empty(&dev->expired));
}
return mask;
}
@@ -172,7 +175,7 @@ misdn_add_timer(struct mISDNtimerdev *dev, int timeout)
struct mISDNtimer *timer;

if (!timeout) {
- dev->work = 1;
+ WRITE_ONCE(dev->work, 1);
wake_up_interruptible(&dev->wait);
id = 0;
} else {
--
2.52.0.457.g6b5491de43-goog

[patchwork-b...@kernel.org]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <ku...@kernel.org>:

On Sun, 18 Jan 2026 13:25:28 +0000 you wrote:
> dev->work can re read locklessly in mISDN_read()
> and mISDN_poll(). Add READ_ONCE()/WRITE_ONCE() annotations.
>
> BUG: KCSAN: data-race in mISDN_ioctl / mISDN_read
>
> write to 0xffff88812d848280 of 4 bytes by task 10864 on cpu 1:
> misdn_add_timer drivers/isdn/mISDN/timerdev.c:175 [inline]
> mISDN_ioctl+0x2fb/0x550 drivers/isdn/mISDN/timerdev.c:233
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:597 [inline]
> __se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
> __x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
> x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>

> [...]

Here is the summary with links:
- [net] mISDN: annotate data-race around dev->work
https://git.kernel.org/netdev/net/c/8175dbf174d4

You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

[Greg Kroah-Hartman]

6.6-stable review patch. If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edum...@google.com>

[ Upstream commit 8175dbf174d487afab81e936a862a8d9b8a1ccb6 ]

dev->work can re read locklessly in mISDN_read()
and mISDN_poll(). Add READ_ONCE()/WRITE_ONCE() annotations.

BUG: KCSAN: data-race in mISDN_ioctl / mISDN_read

write to 0xffff88812d848280 of 4 bytes by task 10864 on cpu 1:
misdn_add_timer drivers/isdn/mISDN/timerdev.c:175 [inline]
mISDN_ioctl+0x2fb/0x550 drivers/isdn/mISDN/timerdev.c:233
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xce/0x140 fs/ioctl.c:583
__x64_sys_ioctl+0x43/0x50 fs/ioctl.c:583
x64_sys_call+0x14b0/0x3000 arch/x86/include/generated/asm/syscalls_64.h:17
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88812d848280 of 4 bytes by task 10857 on cpu 0:
mISDN_read+0x1f2/0x470 drivers/isdn/mISDN/timerdev.c:112
do_loop_readv_writev fs/read_write.c:847 [inline]
vfs_readv+0x3fb/0x690 fs/read_write.c:1020
do_readv+0xe7/0x210 fs/read_write.c:1080
__do_sys_readv fs/read_write.c:1165 [inline]
__se_sys_readv fs/read_write.c:1162 [inline]
__x64_sys_readv+0x45/0x50 fs/read_write.c:1162
x64_sys_call+0x2831/0x3000 arch/x86/include/generated/asm/syscalls_64.h:20

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2c0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000 -> 0x00000001

Fixes: 1b2b03f8e514 ("Add mISDN core files")
Reported-by: syzbot <syzk...@googlegroups.com>
Signed-off-by: Eric Dumazet <edum...@google.com>

Link: https://patch.msgid.link/20260118132528.2...@google.com
Signed-off-by: Jakub Kicinski <ku...@kernel.org>
Signed-off-by: Sasha Levin <sas...@kernel.org>

---
drivers/isdn/mISDN/timerdev.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/isdn/mISDN/timerdev.c b/drivers/isdn/mISDN/timerdev.c

index 83d6b484d3c6c..2ea1887ca2fa0 100644

2.51.0

[Greg Kroah-Hartman]

6.12-stable review patch. If anyone has any objections, please let me know.

index 7cfa8c61dba0a..b2df23234ed3c 100644

[Greg Kroah-Hartman]

6.18-stable review patch. If anyone has any objections, please let me know.

index df98144a95394..33521c328a827 100644

[Greg Kroah-Hartman]

5.10-stable review patch. If anyone has any objections, please let me know.

index abdf36ac3bee5..74d6ed49dc368 100644

[Greg Kroah-Hartman]

5.15-stable review patch. If anyone has any objections, please let me know.

[Greg Kroah-Hartman]

6.1-stable review patch. If anyone has any objections, please let me know.