On 2022/4/21 06:54, Michael Ellerman wrote:
Hangyu Hua <hbh...@gmail.com> writes:
info_release() will be called in device_unregister() when info->dev's
reference count is 0. So there is no need to call ocxl_afu_put() and
kfree() again.
Double frees are often exploitable. But it looks to me like this error
path is not easily reachable by an attacker.
ocxl_file_register_afu() is only called from ocxl_probe(), and we only
go to err_unregister if the sysfs or cdev initialisation fails, which
should only happen if we hit ENOMEM, or we have a duplicate device which
would be a device-tree/hardware error. But maybe Fred can check more
closely, I don't know the driver that well.
cheers
Hi Michael,
You are right. It is hard to exploit at least in my understanding.
That's why I didn't give this to security@. But it still need to be fix
out. By the way, if you are interesting in this kind of bug, you can
check out the other three patches I submitted recently.
rpmsg: virtio: fix possible double free in rpmsg_virtio_add_ctrl_dev()
https://lore.kernel.org/all/20220418101724.42174-1-hbh...@gmail.com/
rpmsg: virtio: fix possible double free in rpmsg_probe()
https://lore.kernel.org/all/20220418093144.40859-1-hbh...@gmail.com/
hwtracing: stm: fix possible double free in stm_register_device()
https://lore.kernel.org/all/20220418081632.35121-1-hbh...@gmail.com/
They are all the similar bugs i could find in the kernel.
Thanks.
Fix this by adding free_minor() and return to err_unregister error path.
Fixes: 75ca758adbaf ("ocxl: Create a clear delineation between ocxl backend &
frontend")
Signed-off-by: Hangyu Hua <hbh...@gmail.com>
---
drivers/misc/ocxl/file.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/misc/ocxl/file.c b/drivers/misc/ocxl/file.c
index d881f5e40ad9..6777c419a8da 100644
--- a/drivers/misc/ocxl/file.c
+++ b/drivers/misc/ocxl/file.c
@@ -556,7 +556,9 @@ int ocxl_file_register_afu(struct ocxl_afu *afu)
err_unregister:
ocxl_sysfs_unregister_afu(info); // safe to call even if register failed
+ free_minor(info);
device_unregister(&info->dev);
+ return rc;
err_put:
ocxl_afu_put(afu);
free_minor(info);
--
2.25.1
