linux-kernel - Re: [PATCH] virtiofs: fix memory leak in virtio_fs

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Date:   Tue, 16 Mar 2021 21:14:45 +0000
From:   Luis Henriques <lhenriques@...e.de>
To:     Vivek Goyal <vgoyal@...hat.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, virtio-fs-list <virtio-fs@...hat.com>
Subject: Re: [PATCH] virtiofs: fix memory leak in virtio_fs_probe()

Vivek Goyal <vgoyal@...hat.com> writes:

> On Tue, Mar 16, 2021 at 05:02:34PM +0000, Luis Henriques wrote:
>> When accidentally passing twice the same tag to qemu, kmemleak ended up
>> reporting a memory leak in virtiofs.  Also, looking at the log I saw the
>> following error (that's when I realised the duplicated tag):
>> 
>>   virtiofs: probe of virtio5 failed with error -17
>> 
>> Here's the kmemleak log for reference:
>> 
>> unreferenced object 0xffff888103d47800 (size 1024):
>>   comm "systemd-udevd", pid 118, jiffies 4294893780 (age 18.340s)
>>   hex dump (first 32 bytes):
>>     00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00  .....N..........
>>     ff ff ff ff ff ff ff ff 80 90 02 a0 ff ff ff ff  ................
>>   backtrace:
>>     [<000000000ebb87c1>] virtio_fs_probe+0x171/0x7ae [virtiofs]
>>     [<00000000f8aca419>] virtio_dev_probe+0x15f/0x210
>>     [<000000004d6baf3c>] really_probe+0xea/0x430
>>     [<00000000a6ceeac8>] device_driver_attach+0xa8/0xb0
>>     [<00000000196f47a7>] __driver_attach+0x98/0x140
>>     [<000000000b20601d>] bus_for_each_dev+0x7b/0xc0
>>     [<00000000399c7b7f>] bus_add_driver+0x11b/0x1f0
>>     [<0000000032b09ba7>] driver_register+0x8f/0xe0
>>     [<00000000cdd55998>] 0xffffffffa002c013
>>     [<000000000ea196a2>] do_one_initcall+0x64/0x2e0
>>     [<0000000008f727ce>] do_init_module+0x5c/0x260
>>     [<000000003cdedab6>] __do_sys_finit_module+0xb5/0x120
>>     [<00000000ad2f48c6>] do_syscall_64+0x33/0x40
>>     [<00000000809526b5>] entry_SYSCALL_64_after_hwframe+0x44/0xae
>> 
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Luis Henriques <lhenriques@...e.de>
>
> Hi Luis,
>
> Thanks for the report and the fix. So looks like leak is happening
> because we are not doing kfree(fs->vqs) in error path.

Yep!

>> ---
>>  fs/fuse/virtio_fs.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c
>> index 8868ac31a3c0..4e6ef9f24e84 100644
>> --- a/fs/fuse/virtio_fs.c
>> +++ b/fs/fuse/virtio_fs.c
>> @@ -899,7 +899,7 @@ static int virtio_fs_probe(struct virtio_device *vdev)
>>  
>>  out:
>>  	vdev->priv = NULL;
>> -	kfree(fs);
>> +	virtio_fs_put(fs);
>
> [ CC virtio-fs list ]

Oops, forgot to include it.  Maybe it should be added to the MAINTAINERS
file (although IIRC it's not an open list).

> fs object is not fully formed. So calling virtio_fs_put() is little odd.
> I will expect it to be called if somebody takes a reference using _get()
> or in the final virtio_fs_remove() when creation reference should go
> away.
>
> How about open coding it and free fs->vqs explicitly. Something like
> as follows.

Ok, I'll send v2 later (I'm currently away from my devel workstation).  To
be honest, my initial version was doing exactly what you're suggesting.  I
decided to change to virtio_fs_put() because the refcount was already
initialised early in the function.  Bad decision.

Cheers,
-- 
Luis

>
> @@ -896,7 +896,7 @@ static int virtio_fs_probe(struct virtio
>  out_vqs:
>         vdev->config->reset(vdev);
>         virtio_fs_cleanup_vqs(vdev, fs);
> -
> +       kfree(fs->vqs);
>  out:
>         vdev->priv = NULL;
>         kfree(fs);
>
> Thanks
> Vivek
>