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SubjectRe: [PATCH][next] vpda: Fix memory leaks of msg on error return paths
On Fri, Jan 22, 2021 at 02:52:35PM +0000, Colin King wrote:
>From: Colin Ian King <colin.king@canonical.com>
>
>There are two error return paths that neglect to free the allocated
>object msg that lead to memory leaks. Fix this by adding an error
>exit path that frees msg.
>
>Addresses-Coverity: ("Resource leak")
>Fixes: 39502d042a70 ("vdpa: Enable user to query vdpa device info")
>Signed-off-by: Colin Ian King <colin.king@canonical.com>
>---
> drivers/vdpa/vdpa.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
>index 9700a0adcca0..eb1f5a514103 100644
>--- a/drivers/vdpa/vdpa.c
>+++ b/drivers/vdpa/vdpa.c
>@@ -540,13 +540,15 @@ static int vdpa_nl_cmd_dev_get_doit(struct sk_buff *skb, struct genl_info *info)
> if (!dev) {
> mutex_unlock(&vdpa_dev_mutex);
> NL_SET_ERR_MSG_MOD(info->extack, "device not found");
>- return -ENODEV;
>+ err = -ENODEV;
>+ goto err;
> }
> vdev = container_of(dev, struct vdpa_device, dev);
> if (!vdev->mdev) {
> mutex_unlock(&vdpa_dev_mutex);
> put_device(dev);
>- return -EINVAL;
>+ err = -EINVAL;
>+ goto err;
> }
> err = vdpa_dev_fill(vdev, msg, info->snd_portid, info->snd_seq, 0, info->extack);
> if (!err)
>@@ -554,6 +556,7 @@ static int vdpa_nl_cmd_dev_get_doit(struct sk_buff *skb, struct genl_info *info)
> put_device(dev);
> mutex_unlock(&vdpa_dev_mutex);
>
>+err:
> if (err)
> nlmsg_free(msg);
> return err;

The patch looks okay, but reviewing it I figure out that if
genlmsg_reply() returns an error, it also frees the sk_buff passed, so
IIUC calling nlmsg_free() when genlmsg_reply() fails should cause a
double free.

Maybe we should do something like this (not tested):

diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
index 9700a0adcca0..920afcb4aa75 100644
--- a/drivers/vdpa/vdpa.c
+++ b/drivers/vdpa/vdpa.c
@@ -538,24 +538,29 @@ static int vdpa_nl_cmd_dev_get_doit(struct sk_buff *skb, struct genl_info *info)
mutex_lock(&vdpa_dev_mutex);
dev = bus_find_device(&vdpa_bus, NULL, devname, vdpa_name_match);
if (!dev) {
- mutex_unlock(&vdpa_dev_mutex);
NL_SET_ERR_MSG_MOD(info->extack, "device not found");
- return -ENODEV;
+ err= -ENODEV;
+ goto err_msg;
}
vdev = container_of(dev, struct vdpa_device, dev);
if (!vdev->mdev) {
- mutex_unlock(&vdpa_dev_mutex);
- put_device(dev);
- return -EINVAL;
+ err = -EINVAL;
+ goto err_dev;
}
err = vdpa_dev_fill(vdev, msg, info->snd_portid, info->snd_seq, 0, info->extack);
- if (!err)
- err = genlmsg_reply(msg, info);
+ if (err)
+ goto err_dev;
+
put_device(dev);
mutex_unlock(&vdpa_dev_mutex);

- if (err)
- nlmsg_free(msg);
+ return genlmsg_reply(msg, info);
+
+err_dev:
+ put_device(dev);
+err_msg:
+ mutex_unlock(&vdpa_dev_mutex);
+ nlmsg_free(msg);
return err;
}

Thanks,
Stefano

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