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authorVladis Dronov <vdronov@redhat.com>2019-12-27 03:26:27 +0100
committerDavid S. Miller <davem@davemloft.net>2019-12-30 20:19:27 -0800
commita33121e5487b424339636b25c35d3a180eaa5f5e (patch)
tree3eb51e254b2b556f109552d2e78311e8f89545f8 /drivers/ptp/ptp_clock.c
parent54fa49ee88138756df0fcf867cb1849904710a8c (diff)
ptp: fix the race between the release of ptp_clock and cdev
In a case when a ptp chardev (like /dev/ptp0) is open but an underlying device is removed, closing this file leads to a race. This reproduces easily in a kvm virtual machine: ts# cat openptp0.c int main() { ... fp = fopen("/dev/ptp0", "r"); ... sleep(10); } ts# uname -r 5.5.0-rc3-46cf053e ts# cat /proc/cmdline ... slub_debug=FZP ts# modprobe ptp_kvm ts# ./openptp0 & [1] 670 opened /dev/ptp0, sleeping 10s... ts# rmmod ptp_kvm ts# ls /dev/ptp* ls: cannot access '/dev/ptp*': No such file or directory ts# ...woken up [ 48.010809] general protection fault: 0000 [#1] SMP [ 48.012502] CPU: 6 PID: 658 Comm: openptp0 Not tainted 5.5.0-rc3-46cf053e #25 [ 48.014624] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), ... [ 48.016270] RIP: 0010:module_put.part.0+0x7/0x80 [ 48.017939] RSP: 0018:ffffb3850073be00 EFLAGS: 00010202 [ 48.018339] RAX: 000000006b6b6b6b RBX: 6b6b6b6b6b6b6b6b RCX: ffff89a476c00ad0 [ 48.018936] RDX: fffff65a08d3ea08 RSI: 0000000000000247 RDI: 6b6b6b6b6b6b6b6b [ 48.019470] ... ^^^ a slub poison [ 48.023854] Call Trace: [ 48.024050] __fput+0x21f/0x240 [ 48.024288] task_work_run+0x79/0x90 [ 48.024555] do_exit+0x2af/0xab0 [ 48.024799] ? vfs_write+0x16a/0x190 [ 48.025082] do_group_exit+0x35/0x90 [ 48.025387] __x64_sys_exit_group+0xf/0x10 [ 48.025737] do_syscall_64+0x3d/0x130 [ 48.026056] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 48.026479] RIP: 0033:0x7f53b12082f6 [ 48.026792] ... [ 48.030945] Modules linked in: ptp i6300esb watchdog [last unloaded: ptp_kvm] [ 48.045001] Fixing recursive fault but reboot is needed! This happens in: static void __fput(struct file *file) { ... if (file->f_op->release) file->f_op->release(inode, file); <<< cdev is kfree'd here if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL && !(mode & FMODE_PATH))) { cdev_put(inode->i_cdev); <<< cdev fields are accessed here Namely: __fput() posix_clock_release() kref_put(&clk->kref, delete_clock) <<< the last reference delete_clock() delete_ptp_clock() kfree(ptp) <<< cdev is embedded in ptp cdev_put module_put(p->owner) <<< *p is kfree'd, bang! Here cdev is embedded in posix_clock which is embedded in ptp_clock. The race happens because ptp_clock's lifetime is controlled by two refcounts: kref and cdev.kobj in posix_clock. This is wrong. Make ptp_clock's sysfs device a parent of cdev with cdev_device_add() created especially for such cases. This way the parent device with its ptp_clock is not released until all references to the cdev are released. This adds a requirement that an initialized but not exposed struct device should be provided to posix_clock_register() by a caller instead of a simple dev_t. This approach was adopted from the commit 72139dfa2464 ("watchdog: Fix the race between the release of watchdog_core_data and cdev"). See details of the implementation in the commit 233ed09d7fda ("chardev: add helper function to register char devs with a struct device"). Link: https://lore.kernel.org/linux-fsdevel/20191125125342.6189-1-vdronov@redhat.com/T/#u Analyzed-by: Stephen Johnston <sjohnsto@redhat.com> Analyzed-by: Vern Lovejoy <vlovejoy@redhat.com> Signed-off-by: Vladis Dronov <vdronov@redhat.com> Acked-by: Richard Cochran <richardcochran@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/ptp/ptp_clock.c')
-rw-r--r--drivers/ptp/ptp_clock.c31
1 files changed, 14 insertions, 17 deletions
diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
index e60eab7f8a61..61fafe0374ce 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -166,9 +166,9 @@ static struct posix_clock_operations ptp_clock_ops = {
.read = ptp_read,
};
-static void delete_ptp_clock(struct posix_clock *pc)
+static void ptp_clock_release(struct device *dev)
{
- struct ptp_clock *ptp = container_of(pc, struct ptp_clock, clock);
+ struct ptp_clock *ptp = container_of(dev, struct ptp_clock, dev);
mutex_destroy(&ptp->tsevq_mux);
mutex_destroy(&ptp->pincfg_mux);
@@ -213,7 +213,6 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
}
ptp->clock.ops = ptp_clock_ops;
- ptp->clock.release = delete_ptp_clock;
ptp->info = info;
ptp->devid = MKDEV(major, index);
ptp->index = index;
@@ -236,15 +235,6 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
if (err)
goto no_pin_groups;
- /* Create a new device in our class. */
- ptp->dev = device_create_with_groups(ptp_class, parent, ptp->devid,
- ptp, ptp->pin_attr_groups,
- "ptp%d", ptp->index);
- if (IS_ERR(ptp->dev)) {
- err = PTR_ERR(ptp->dev);
- goto no_device;
- }
-
/* Register a new PPS source. */
if (info->pps) {
struct pps_source_info pps;
@@ -260,8 +250,18 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
}
}
- /* Create a posix clock. */
- err = posix_clock_register(&ptp->clock, ptp->devid);
+ /* Initialize a new device of our class in our clock structure. */
+ device_initialize(&ptp->dev);
+ ptp->dev.devt = ptp->devid;
+ ptp->dev.class = ptp_class;
+ ptp->dev.parent = parent;
+ ptp->dev.groups = ptp->pin_attr_groups;
+ ptp->dev.release = ptp_clock_release;
+ dev_set_drvdata(&ptp->dev, ptp);
+ dev_set_name(&ptp->dev, "ptp%d", ptp->index);
+
+ /* Create a posix clock and link it to the device. */
+ err = posix_clock_register(&ptp->clock, &ptp->dev);
if (err) {
pr_err("failed to create posix clock\n");
goto no_clock;
@@ -273,8 +273,6 @@ no_clock:
if (ptp->pps_source)
pps_unregister_source(ptp->pps_source);
no_pps:
- device_destroy(ptp_class, ptp->devid);
-no_device:
ptp_cleanup_pin_groups(ptp);
no_pin_groups:
if (ptp->kworker)
@@ -304,7 +302,6 @@ int ptp_clock_unregister(struct ptp_clock *ptp)
if (ptp->pps_source)
pps_unregister_source(ptp->pps_source);
- device_destroy(ptp_class, ptp->devid);
ptp_cleanup_pin_groups(ptp);
posix_clock_unregister(&ptp->clock);