Re: [PATCH] pps: fix warning in pps_register_cdev when register device fail
From: Wang Liang
Date: Fri Aug 29 2025 - 05:35:33 EST
在 2025/8/28 21:24, Calvin Owens 写道:
On Wednesday 08/27 at 08:32 -0700, Calvin Owens wrote:
On Wednesday 08/27 at 14:50 +0800, Wang Liang wrote:
Similar to previous commit 2a934fdb01db ("media: v4l2-dev: fix error
handling in __video_register_device()"), the release hook should be set
before device_register(). Otherwise, when device_register() return error
and put_device() try to callback the release function, the below warning
may happen.
------------[ cut here ]------------
WARNING: CPU: 1 PID: 4760 at drivers/base/core.c:2567 device_release+0x1bd/0x240 drivers/base/core.c:2567
Modules linked in:
CPU: 1 UID: 0 PID: 4760 Comm: syz.4.914 Not tainted 6.17.0-rc3+ #1 NONE
RIP: 0010:device_release+0x1bd/0x240 drivers/base/core.c:2567
Call Trace:
<TASK>
kobject_cleanup+0x136/0x410 lib/kobject.c:689
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0xe9/0x130 lib/kobject.c:737
put_device+0x24/0x30 drivers/base/core.c:3797
pps_register_cdev+0x2da/0x370 drivers/pps/pps.c:402
pps_register_source+0x2f6/0x480 drivers/pps/kapi.c:108
pps_tty_open+0x190/0x310 drivers/pps/clients/pps-ldisc.c:57
tty_ldisc_open+0xa7/0x120 drivers/tty/tty_ldisc.c:432
tty_set_ldisc+0x333/0x780 drivers/tty/tty_ldisc.c:563
tiocsetd drivers/tty/tty_io.c:2429 [inline]
tty_ioctl+0x5d1/0x1700 drivers/tty/tty_io.c:2728
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:598 [inline]
__se_sys_ioctl fs/ioctl.c:584 [inline]
__x64_sys_ioctl+0x194/0x210 fs/ioctl.c:584
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x5f/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x76/0x7e
</TASK>
Before commit c79a39dc8d06 ("pps: Fix a use-after-free"),
pps_register_cdev() call device_create() to create pps->dev, which will
init dev->release to device_create_release(). Now the comment is outdated,
just remove it.
Hi Wang,
I'm curious why pps_register_cdev() is failing, is there possibly a
second issue to investigate there? Or was it fault injection?
Otherwise, makes perfect sense to me. I'm new to this code, so grain of
salt, but since I exposed it:
Reviewed-by: Calvin Owens <calvin@xxxxxxxxxx>
I apologize Wang, I missed something when I looked at this yesterday:
I think your patch introduces a double-free, because the pps object is
already freed by pps_register_source() when pps_register_cdev() returns
an error. Because put_device() was a nop with the missing release_fn, it
wasn't actually doing anything. That's very confusing, and my fault.
You are right! Thanks for the reminder. I reproduce the double-free issue:
==================================================================
BUG: KASAN: double-free in pps_register_source+0x2c1/0x3a0
Free of addr ffff8881078fd800 by task insmod/323
Call Trace:
<TASK>
dump_stack_lvl+0x55/0x70
print_report+0xcb/0x610
kasan_report_invalid_free+0x94/0xc0
check_slab_allocation+0x105/0x130
kfree+0xba/0x360
pps_register_source+0x2c1/0x3a0
It is triggered by kzalloc fail in device_private_init().
Your patch is clearly an improvement. But I think you additionally need
to remove the 'kfree_pps' error logic at the bottom of
pps_register_source() to avoid a double free in the failure case:
Thanks for your suggestions, it is helpful!
I will send a v2 patch later. Thanks!
------
Best regards
Wang Liang
diff --git a/drivers/pps/kapi.c b/drivers/pps/kapi.c
index 92d1b62ea239..4d0ba35590a3 100644
--- a/drivers/pps/kapi.c
+++ b/drivers/pps/kapi.c
@@ -116,9 +116,6 @@ struct pps_device *pps_register_source(struct pps_source_info *info,
return pps;
-kfree_pps:
- kfree(pps);
-
pps_register_source_exit:
pr_err("%s: unable to register source\n", info->name);
The only reason I put that kfree() there is because I noticed the memory
was being leaked in the failure case. Doh. Your patch makes this right.
Thanks,
Calvin
Fixes: c79a39dc8d06 ("pps: Fix a use-after-free")
Signed-off-by: Wang Liang <wangliang74@xxxxxxxxxx>
---
drivers/pps/pps.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/drivers/pps/pps.c b/drivers/pps/pps.c
index 9463232af8d2..0d2d57250575 100644
--- a/drivers/pps/pps.c
+++ b/drivers/pps/pps.c
@@ -383,13 +383,11 @@ int pps_register_cdev(struct pps_device *pps)
pps->dev.devt = MKDEV(pps_major, pps->id);
dev_set_drvdata(&pps->dev, pps);
dev_set_name(&pps->dev, "pps%d", pps->id);
+ pps->dev.release = pps_device_destruct;
err = device_register(&pps->dev);
if (err)
goto free_idr;
- /* Override the release function with our own */
- pps->dev.release = pps_device_destruct;
-
pr_debug("source %s got cdev (%d:%d)\n", pps->info.name, pps_major,
pps->id);
--
2.33.0