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

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Date:   Tue, 16 Mar 2021 14:17:18 -0400
From:   Vivek Goyal <vgoyal@...hat.com>
To:     Luis Henriques <lhenriques@...e.de>
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()

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.

> ---
>  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 ]

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.

@@ -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