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xen/gntdev: fix error handling in ioctl

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When gntdev_ioctl_map_grant_ref() fails to copy the operation result
back to userspace after successfully adding the mapping to the list,
the error path returns -EFAULT without releasing the reference
acquired by gntdev_alloc_map(). The mapping remains in priv->maps
with a refcount of 1, causing a memory leak and a dangling list
entry.

Additionally, gntdev_add_map() may modify map->index to avoid overlap
with existing mappings. Therefore, the index returned to userspace
must be obtained after gntdev_add_map() completes.

Fix this by holding the mutex across gntdev_add_map(), retrieving
the correct index, and copy_to_user(). If copy_to_user() fails,
remove the mapping from the list and release the reference while
still holding the lock.

Cc: stable@vger.kernel.org

Fix these issues by properly handling all error cases.

Fixes: 1401c00e59 ("xen/gntdev: convert priv->lock to a mutex")
Fixes: 68b025c813 ("xen-gntdev: Add reference counting to maps")

Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20260622112541.38194-1-vulab@iscas.ac.cn>
This commit is contained in:
Wentao Liang
2026-07-01 09:51:09 +02:00
committed by Juergen Gross
parent 26d060ba39
commit 45ca1afe2f
1 changed files with 6 additions and 2 deletions
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drivers/xen/gntdev.c
+6 -2
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@@ -670,11 +670,15 @@ static long gntdev_ioctl_map_grant_ref(struct gntdev_priv *priv,
mutex_lock(&priv->lock);
gntdev_add_map(priv, map);
op.index = map->index << PAGE_SHIFT;
mutex_unlock(&priv->lock);
if (copy_to_user(u, &op, sizeof(op)) != 0)
if (copy_to_user(u, &op, sizeof(op)) != 0) {
list_del(&map->next);
mutex_unlock(&priv->lock);
gntdev_put_map(priv, map);
return -EFAULT;
}
mutex_unlock(&priv->lock);
return 0;
}