On 3/4/20 3:58 AM, Cengiz Can wrote:
> There was a recent change in blktrace.c that added a RCU protection to
> `q->blk_trace` in order to fix a use-after-free issue during access.
>
> However the change missed an edge case that can lead to dereferencing of
> `bt` pointer even when it's NULL:
>
> Coverity static analyzer marked this as a FORWARD_NULL issue with CID
> 1460458.
>
> ```
> /kernel/trace/blktrace.c: 1904 in sysfs_blk_trace_attr_store()
> 1898 ret = 0;
> 1899 if (bt == NULL)
> 1900 ret = blk_trace_setup_queue(q, bdev);
> 1901
> 1902 if (ret == 0) {
> 1903 if (attr == &dev_attr_act_mask)
>>>> CID 1460458: Null pointer dereferences (FORWARD_NULL)
>>>> Dereferencing null pointer "bt".
> 1904 bt->act_mask = value;
> 1905 else if (attr == &dev_attr_pid)
> 1906 bt->pid = value;
> 1907 else if (attr == &dev_attr_start_lba)
> 1908 bt->start_lba = value;
> 1909 else if (attr == &dev_attr_end_lba)
> ```
>
> Added a reassignment with RCU annotation to fix the issue.
Applied, thanks.
--
Jens Axboe
