91932db1d9
commit c79a39dc8d060b9e64e8b0fa9d245d44befeefbe upstream.
On a board running ntpd and gpsd, I'm seeing a consistent use-after-free
in sys_exit() from gpsd when rebooting:
pps pps1: removed
------------[ cut here ]------------
kobject: '(null)' (00000000db4bec24): is not initialized, yet kobject_put() is being called.
WARNING: CPU: 2 PID: 440 at lib/kobject.c:734 kobject_put+0x120/0x150
CPU: 2 UID: 299 PID: 440 Comm: gpsd Not tainted 6.11.0-rc6-00308-gb31c44928842 #1
Hardware name: Raspberry Pi 4 Model B Rev 1.1 (DT)
pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : kobject_put+0x120/0x150
lr : kobject_put+0x120/0x150
sp : ffffffc0803d3ae0
x29: ffffffc0803d3ae0 x28: ffffff8042dc9738 x27: 0000000000000001
x26: 0000000000000000 x25: ffffff8042dc9040 x24: ffffff8042dc9440
x23: ffffff80402a4620 x22: ffffff8042ef4bd0 x21: ffffff80405cb600
x20: 000000000008001b x19: ffffff8040b3b6e0 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 696e6920746f6e20
x14: 7369203a29343263 x13: 205d303434542020 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000000 x3 : 0000000000000000
x2 : 0000000000000000 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
kobject_put+0x120/0x150
cdev_put+0x20/0x3c
__fput+0x2c4/0x2d8
____fput+0x1c/0x38
task_work_run+0x70/0xfc
do_exit+0x2a0/0x924
do_group_exit+0x34/0x90
get_signal+0x7fc/0x8c0
do_signal+0x128/0x13b4
do_notify_resume+0xdc/0x160
el0_svc+0xd4/0xf8
el0t_64_sync_handler+0x140/0x14c
el0t_64_sync+0x190/0x194
---[ end trace 0000000000000000 ]---
...followed by more symptoms of corruption, with similar stacks:
refcount_t: underflow; use-after-free.
kernel BUG at lib/list_debug.c:62!
Kernel panic - not syncing: Oops - BUG: Fatal exception
This happens because pps_device_destruct() frees the pps_device with the
embedded cdev immediately after calling cdev_del(), but, as the comment
above cdev_del() notes, fops for previously opened cdevs are still
callable even after cdev_del() returns. I think this bug has always
been there: I can't explain why it suddenly started happening every time
I reboot this particular board.
In commit d953e0e837 ("pps: Fix a use-after free bug when
unregistering a source."), George Spelvin suggested removing the
embedded cdev. That seems like the simplest way to fix this, so I've
implemented his suggestion, using __register_chrdev() with pps_idr
becoming the source of truth for which minor corresponds to which
device.
But now that pps_idr defines userspace visibility instead of cdev_add(),
we need to be sure the pps->dev refcount can't reach zero while
userspace can still find it again. So, the idr_remove() call moves to
pps_unregister_cdev(), and pps_idr now holds a reference to pps->dev.
pps_core: source serial1 got cdev (251:1)
<...>
pps pps1: removed
pps_core: unregistering pps1
pps_core: deallocating pps1
Fixes: d953e0e837 ("pps: Fix a use-after free bug when unregistering a source.")
Cc: stable@vger.kernel.org
Signed-off-by: Calvin Owens <calvin@wbinvd.org>
Reviewed-by: Michal Schmidt <mschmidt@redhat.com>
Link: https://lore.kernel.org/r/a17975fd5ae99385791929e563f72564edbcf28f.1731383727.git.calvin@wbinvd.org
Signed-off-by: Calvin Owens <calvin@wbinvd.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
88 lines
1.7 KiB
C
88 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* pps-ktimer.c -- kernel timer test client
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*
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* Copyright (C) 2005-2006 Rodolfo Giometti <giometti@linux.it>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/time.h>
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#include <linux/timer.h>
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#include <linux/pps_kernel.h>
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/*
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* Global variables
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*/
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static struct pps_device *pps;
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static struct timer_list ktimer;
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/*
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* The kernel timer
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*/
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static void pps_ktimer_event(struct timer_list *unused)
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{
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struct pps_event_time ts;
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/* First of all we get the time stamp... */
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pps_get_ts(&ts);
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pps_event(pps, &ts, PPS_CAPTUREASSERT, NULL);
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mod_timer(&ktimer, jiffies + HZ);
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}
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/*
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* The PPS info struct
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*/
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static struct pps_source_info pps_ktimer_info = {
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.name = "ktimer",
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.path = "",
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.mode = PPS_CAPTUREASSERT | PPS_OFFSETASSERT |
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PPS_ECHOASSERT |
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PPS_CANWAIT | PPS_TSFMT_TSPEC,
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.owner = THIS_MODULE,
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};
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/*
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* Module staff
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*/
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static void __exit pps_ktimer_exit(void)
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{
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dev_dbg(&pps->dev, "ktimer PPS source unregistered\n");
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del_timer_sync(&ktimer);
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pps_unregister_source(pps);
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}
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static int __init pps_ktimer_init(void)
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{
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pps = pps_register_source(&pps_ktimer_info,
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PPS_CAPTUREASSERT | PPS_OFFSETASSERT);
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if (IS_ERR(pps)) {
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pr_err("cannot register PPS source\n");
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return PTR_ERR(pps);
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}
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timer_setup(&ktimer, pps_ktimer_event, 0);
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mod_timer(&ktimer, jiffies + HZ);
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dev_dbg(&pps->dev, "ktimer PPS source registered\n");
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return 0;
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}
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module_init(pps_ktimer_init);
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module_exit(pps_ktimer_exit);
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MODULE_AUTHOR("Rodolfo Giometti <giometti@linux.it>");
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MODULE_DESCRIPTION("dummy PPS source by using a kernel timer (just for debug)");
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MODULE_LICENSE("GPL");
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