Messages in this thread | | | Date | Thu, 21 Apr 2022 10:35:52 +0800 | Subject | Re: [PATCH] misc: ocxl: fix possible double free in ocxl_file_register_afu | From | Hangyu Hua <> |
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On 2022/4/21 06:54, Michael Ellerman wrote: > Hangyu Hua <hbh25y@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-hbh25y@gmail.com/
rpmsg: virtio: fix possible double free in rpmsg_probe() https://lore.kernel.org/all/20220418093144.40859-1-hbh25y@gmail.com/
hwtracing: stm: fix possible double free in stm_register_device() https://lore.kernel.org/all/20220418081632.35121-1-hbh25y@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 <hbh25y@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
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