Re: [PATCH] virtiofs: fix memory leak in virtio_fs_probe()

Vivek Goyal [off-list ref] writes:

On Tue, Mar 16, 2021 at 05:02:34PM +0000, Luis Henriques wrote:

quoted

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@vger.kernel.org
Signed-off-by: Luis Henriques <redacted>

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!

quoted

---
 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