[PATCH] drivers/base: Fix memory leak in error paths

[PATCH] drivers/base: Fix memory leak in error paths

[jouni.hogander]

From: Jouni Hogander <jouni.hogander@unikie.com>

Currently error paths are using device_del to clean-up preparations
done by device_add. This is causing memory leak as free of dev->p
allocated in device_add is freed in device_release. This is fixed by
moving freeing dev->p to counterpart of device_add i.e. device_del.

This memory leak was reported by Syzkaller:

BUG: memory leak unreferenced object 0xffff8880675ca008 (size 256):
  comm "netdev_register", pid 281, jiffies 4294696663 (age 6.808s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  backtrace:
    [<0000000058ca4711>] kmem_cache_alloc_trace+0x167/0x280
    [<000000002340019b>] device_add+0x882/0x1750
    [<000000001d588c3a>] netdev_register_kobject+0x128/0x380
    [<0000000011ef5535>] register_netdevice+0xa1b/0xf00
    [<000000007fcf1c99>] __tun_chr_ioctl+0x20d5/0x3dd0
    [<000000006a5b7b2b>] tun_chr_ioctl+0x2f/0x40
    [<00000000f30f834a>] do_vfs_ioctl+0x1c7/0x1510
    [<00000000fba062ea>] ksys_ioctl+0x99/0xb0
    [<00000000b1c1b8d2>] __x64_sys_ioctl+0x78/0xb0
    [<00000000984cabb9>] do_syscall_64+0x16f/0x580
    [<000000000bde033d>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
    [<00000000e6ca2d9f>] 0xffffffffffffffff

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Jouni Hogander <jouni.hogander@unikie.com>
---
 drivers/base/core.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 7bd9cd366d41..cb4b27e82a9f 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1080,7 +1080,6 @@ EXPORT_SYMBOL_GPL(device_show_bool);
 static void device_release(struct kobject *kobj)
 {
 	struct device *dev = kobj_to_dev(kobj);
-	struct device_private *p = dev->p;
 
 	/*
 	 * Some platform devices are driven without driver attached
@@ -1102,7 +1101,6 @@ static void device_release(struct kobject *kobj)
 	else
 		WARN(1, KERN_ERR "Device '%s' does not have a release() function, it is broken and must be fixed. See Documentation/kobject.txt.\n",
 			dev_name(dev));
-	kfree(p);
 }
 
 static const void *device_namespace(struct kobject *kobj)
@@ -2388,6 +2386,7 @@ void device_del(struct device *dev)
 	kobject_del(&dev->kobj);
 	cleanup_glue_dir(dev, glue_dir);
 	put_device(parent);
+	kfree(dev->p);
 }
 EXPORT_SYMBOL_GPL(device_del);
 
-- 
2.17.1

Re: [PATCH] drivers/base: Fix memory leak in error paths

[Greg Kroah-Hartman]

On Thu, Nov 14, 2019 at 02:18:40PM +0200, jouni.hogander@unikie.com wrote:
> From: Jouni Hogander <jouni.hogander@unikie.com>
> 
> Currently error paths are using device_del to clean-up preparations
> done by device_add. This is causing memory leak as free of dev->p
> allocated in device_add is freed in device_release. This is fixed by
> moving freeing dev->p to counterpart of device_add i.e. device_del.

Are you sure that is safe?  The device can still be "alive" after
device_del() is called.  The only place you know that it should be freed
is in the release callback.

> This memory leak was reported by Syzkaller:
> 
> BUG: memory leak unreferenced object 0xffff8880675ca008 (size 256):
>   comm "netdev_register", pid 281, jiffies 4294696663 (age 6.808s)
>   hex dump (first 32 bytes):
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>   backtrace:
>     [<0000000058ca4711>] kmem_cache_alloc_trace+0x167/0x280
>     [<000000002340019b>] device_add+0x882/0x1750
>     [<000000001d588c3a>] netdev_register_kobject+0x128/0x380
>     [<0000000011ef5535>] register_netdevice+0xa1b/0xf00
>     [<000000007fcf1c99>] __tun_chr_ioctl+0x20d5/0x3dd0
>     [<000000006a5b7b2b>] tun_chr_ioctl+0x2f/0x40
>     [<00000000f30f834a>] do_vfs_ioctl+0x1c7/0x1510
>     [<00000000fba062ea>] ksys_ioctl+0x99/0xb0
>     [<00000000b1c1b8d2>] __x64_sys_ioctl+0x78/0xb0
>     [<00000000984cabb9>] do_syscall_64+0x16f/0x580
>     [<000000000bde033d>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>     [<00000000e6ca2d9f>] 0xffffffffffffffff

How is this a leak?  This is in device_add(), not removing the device.
When the structure really is freed then it can be removed.

Or are you triggering an error in device_add() somehow to trigger this
callback?

thanks,

greg k-h

Re: [PATCH] drivers/base: Fix memory leak in error paths

[Jouni Högander]

Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:

> On Thu, Nov 14, 2019 at 02:18:40PM +0200, jouni.hogander@unikie.com wrote:
>> From: Jouni Hogander <jouni.hogander@unikie.com>
>> 
>> Currently error paths are using device_del to clean-up preparations
>> done by device_add. This is causing memory leak as free of dev->p
>> allocated in device_add is freed in device_release. This is fixed by
>> moving freeing dev->p to counterpart of device_add i.e. device_del.
>
> Are you sure that is safe?  The device can still be "alive" after
> device_del() is called.  The only place you know that it should be freed
> is in the release callback.

Now as you pointed this out I'm not.

>
>> This memory leak was reported by Syzkaller:
>> 
>> BUG: memory leak unreferenced object 0xffff8880675ca008 (size 256):
>>   comm "netdev_register", pid 281, jiffies 4294696663 (age 6.808s)
>>   hex dump (first 32 bytes):
>>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>>   backtrace:
>>     [<0000000058ca4711>] kmem_cache_alloc_trace+0x167/0x280
>>     [<000000002340019b>] device_add+0x882/0x1750
>>     [<000000001d588c3a>] netdev_register_kobject+0x128/0x380
>>     [<0000000011ef5535>] register_netdevice+0xa1b/0xf00
>>     [<000000007fcf1c99>] __tun_chr_ioctl+0x20d5/0x3dd0
>>     [<000000006a5b7b2b>] tun_chr_ioctl+0x2f/0x40
>>     [<00000000f30f834a>] do_vfs_ioctl+0x1c7/0x1510
>>     [<00000000fba062ea>] ksys_ioctl+0x99/0xb0
>>     [<00000000b1c1b8d2>] __x64_sys_ioctl+0x78/0xb0
>>     [<00000000984cabb9>] do_syscall_64+0x16f/0x580
>>     [<000000000bde033d>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>     [<00000000e6ca2d9f>] 0xffffffffffffffff
>
> How is this a leak?  This is in device_add(), not removing the device.
> When the structure really is freed then it can be removed.

In net/core/net-sysfs.c:netdev_register_kobject device_add allocates
dev->p. Now if register_queue_kobjects fails the error path is calling
device_del and dev->p is never freed. Proper fix here could be to call
put_device after device_del?

>
> Or are you triggering an error in device_add() somehow to trigger this
> callback?

This was found using Syzkaller with fault injection and memory leak
detection enabled. Error is not triggered in device_add but after
device_add.

BR,

Jouni Högander

Re: [PATCH] drivers/base: Fix memory leak in error paths

[Greg Kroah-Hartman]

On Fri, Nov 15, 2019 at 09:59:43AM +0200, Jouni Högander wrote:
> Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
> 
> > On Thu, Nov 14, 2019 at 02:18:40PM +0200, jouni.hogander@unikie.com wrote:
> >> From: Jouni Hogander <jouni.hogander@unikie.com>
> >> 
> >> Currently error paths are using device_del to clean-up preparations
> >> done by device_add. This is causing memory leak as free of dev->p
> >> allocated in device_add is freed in device_release. This is fixed by
> >> moving freeing dev->p to counterpart of device_add i.e. device_del.
> >
> > Are you sure that is safe?  The device can still be "alive" after
> > device_del() is called.  The only place you know that it should be freed
> > is in the release callback.
> 
> Now as you pointed this out I'm not.
> 
> >
> >> This memory leak was reported by Syzkaller:
> >> 
> >> BUG: memory leak unreferenced object 0xffff8880675ca008 (size 256):
> >>   comm "netdev_register", pid 281, jiffies 4294696663 (age 6.808s)
> >>   hex dump (first 32 bytes):
> >>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> >>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> >>   backtrace:
> >>     [<0000000058ca4711>] kmem_cache_alloc_trace+0x167/0x280
> >>     [<000000002340019b>] device_add+0x882/0x1750
> >>     [<000000001d588c3a>] netdev_register_kobject+0x128/0x380
> >>     [<0000000011ef5535>] register_netdevice+0xa1b/0xf00
> >>     [<000000007fcf1c99>] __tun_chr_ioctl+0x20d5/0x3dd0
> >>     [<000000006a5b7b2b>] tun_chr_ioctl+0x2f/0x40
> >>     [<00000000f30f834a>] do_vfs_ioctl+0x1c7/0x1510
> >>     [<00000000fba062ea>] ksys_ioctl+0x99/0xb0
> >>     [<00000000b1c1b8d2>] __x64_sys_ioctl+0x78/0xb0
> >>     [<00000000984cabb9>] do_syscall_64+0x16f/0x580
> >>     [<000000000bde033d>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >>     [<00000000e6ca2d9f>] 0xffffffffffffffff
> >
> > How is this a leak?  This is in device_add(), not removing the device.
> > When the structure really is freed then it can be removed.
> 
> In net/core/net-sysfs.c:netdev_register_kobject device_add allocates
> dev->p. Now if register_queue_kobjects fails the error path is calling
> device_del and dev->p is never freed. Proper fix here could be to call
> put_device after device_del?

Hm, this sounds like you have a reference count leak here, as
put_device() should be properly called already in this case.  You might
want to look further to see where exactly the register_queue_kobjects()
call fails in order to see if we grabbed a reference we forgot to put
back on an error path.

thanks,

greg k-h

Re: [PATCH] drivers/base: Fix memory leak in error paths

[Jouni Högander]

Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:

>> >> This memory leak was reported by Syzkaller:
>> >> 
>> >> BUG: memory leak unreferenced object 0xffff8880675ca008 (size 256):
>> >>   comm "netdev_register", pid 281, jiffies 4294696663 (age 6.808s)
>> >>   hex dump (first 32 bytes):
>> >>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>> >>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>> >>   backtrace:
>> >>     [<0000000058ca4711>] kmem_cache_alloc_trace+0x167/0x280
>> >>     [<000000002340019b>] device_add+0x882/0x1750
>> >>     [<000000001d588c3a>] netdev_register_kobject+0x128/0x380
>> >>     [<0000000011ef5535>] register_netdevice+0xa1b/0xf00
>> >>     [<000000007fcf1c99>] __tun_chr_ioctl+0x20d5/0x3dd0
>> >>     [<000000006a5b7b2b>] tun_chr_ioctl+0x2f/0x40
>> >>     [<00000000f30f834a>] do_vfs_ioctl+0x1c7/0x1510
>> >>     [<00000000fba062ea>] ksys_ioctl+0x99/0xb0
>> >>     [<00000000b1c1b8d2>] __x64_sys_ioctl+0x78/0xb0
>> >>     [<00000000984cabb9>] do_syscall_64+0x16f/0x580
>> >>     [<000000000bde033d>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>> >>     [<00000000e6ca2d9f>] 0xffffffffffffffff
>> >
>> > How is this a leak?  This is in device_add(), not removing the device.
>> > When the structure really is freed then it can be removed.
>> 
>> In net/core/net-sysfs.c:netdev_register_kobject device_add allocates
>> dev->p. Now if register_queue_kobjects fails the error path is calling
>> device_del and dev->p is never freed. Proper fix here could be to call
>> put_device after device_del?
>
> Hm, this sounds like you have a reference count leak here, as
> put_device() should be properly called already in this case.  You might
> want to look further to see where exactly the register_queue_kobjects()
> call fails in order to see if we grabbed a reference we forgot to put
> back on an error path.

Ok, did some more debugging on
this. net/core/net-sysfs.c:netdev_register_kobject is doing
device_initialize(dev). This is in
drivers/base/core.c:device_initialize:

 * NOTE: Use put_device() to give up your reference instead of freeing
 * @dev directly once you have called this function.

My understanding is that remaining reference on error path is taken by
device_initialize and as instructed in the note above it should be given
up using put_device? Tested this and it's fixing the memory leak I found
in my Syzkaller exercise. Addition to that it seems to be fixing also
this one:

https://syzkaller.appspot.com/bug?id=f5f4af9fb9ffb3112ad6e30f717f769decdccdfc

BR,

Jouni Högander

Re: [PATCH] drivers/base: Fix memory leak in error paths

[Greg Kroah-Hartman]

On Fri, Nov 15, 2019 at 12:05:17PM +0200, Jouni Högander wrote:
> Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:
> 
> >> >> This memory leak was reported by Syzkaller:
> >> >> 
> >> >> BUG: memory leak unreferenced object 0xffff8880675ca008 (size 256):
> >> >>   comm "netdev_register", pid 281, jiffies 4294696663 (age 6.808s)
> >> >>   hex dump (first 32 bytes):
> >> >>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> >> >>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> >> >>   backtrace:
> >> >>     [<0000000058ca4711>] kmem_cache_alloc_trace+0x167/0x280
> >> >>     [<000000002340019b>] device_add+0x882/0x1750
> >> >>     [<000000001d588c3a>] netdev_register_kobject+0x128/0x380
> >> >>     [<0000000011ef5535>] register_netdevice+0xa1b/0xf00
> >> >>     [<000000007fcf1c99>] __tun_chr_ioctl+0x20d5/0x3dd0
> >> >>     [<000000006a5b7b2b>] tun_chr_ioctl+0x2f/0x40
> >> >>     [<00000000f30f834a>] do_vfs_ioctl+0x1c7/0x1510
> >> >>     [<00000000fba062ea>] ksys_ioctl+0x99/0xb0
> >> >>     [<00000000b1c1b8d2>] __x64_sys_ioctl+0x78/0xb0
> >> >>     [<00000000984cabb9>] do_syscall_64+0x16f/0x580
> >> >>     [<000000000bde033d>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> >> >>     [<00000000e6ca2d9f>] 0xffffffffffffffff
> >> >
> >> > How is this a leak?  This is in device_add(), not removing the device.
> >> > When the structure really is freed then it can be removed.
> >> 
> >> In net/core/net-sysfs.c:netdev_register_kobject device_add allocates
> >> dev->p. Now if register_queue_kobjects fails the error path is calling
> >> device_del and dev->p is never freed. Proper fix here could be to call
> >> put_device after device_del?
> >
> > Hm, this sounds like you have a reference count leak here, as
> > put_device() should be properly called already in this case.  You might
> > want to look further to see where exactly the register_queue_kobjects()
> > call fails in order to see if we grabbed a reference we forgot to put
> > back on an error path.
> 
> Ok, did some more debugging on
> this. net/core/net-sysfs.c:netdev_register_kobject is doing
> device_initialize(dev). This is in
> drivers/base/core.c:device_initialize:
> 
>  * NOTE: Use put_device() to give up your reference instead of freeing
>  * @dev directly once you have called this function.
> 
> My understanding is that remaining reference on error path is taken by
> device_initialize and as instructed in the note above it should be given
> up using put_device?

Yes, that is correct.

> Tested this and it's fixing the memory leak I found in my Syzkaller
> exercise. Addition to that it seems to be fixing also this one:
> 
> https://syzkaller.appspot.com/bug?id=f5f4af9fb9ffb3112ad6e30f717f769decdccdfc

Great!  Care to submit a patch for this?

thanks,

greg k-h

Re: [PATCH] drivers/base: Fix memory leak in error paths

[Jouni Högander]

Greg Kroah-Hartman <gregkh@linuxfoundation.org> writes:

>> 
>> Ok, did some more debugging on
>> this. net/core/net-sysfs.c:netdev_register_kobject is doing
>> device_initialize(dev). This is in
>> drivers/base/core.c:device_initialize:
>> 
>>  * NOTE: Use put_device() to give up your reference instead of freeing
>>  * @dev directly once you have called this function.
>> 
>> My understanding is that remaining reference on error path is taken by
>> device_initialize and as instructed in the note above it should be given
>> up using put_device?
>
> Yes, that is correct.
>
>> Tested this and it's fixing the memory leak I found in my Syzkaller
>> exercise. Addition to that it seems to be fixing also this one:
>> 
>> https://syzkaller.appspot.com/bug?id=f5f4af9fb9ffb3112ad6e30f717f769decdccdfc
>
> Great!  Care to submit a patch for this?

I will submit another patch and Cc you there. This patch should be ignored.

BR,

Jouni Högander