blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats() When blkg_alloc() is called to allocate a blkcg_gq structure with the associated blkg_iostat_set's, there are 2 fields within blkg_iostat_set that requires proper initialization - blkg & sync. The former field was introduced by commit 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()") while the later one was introduced by commit f73316482977 ("blk-cgroup: reimplement basic IO stats using cgroup rstat"). Unfortunately those fields in the blkg_iostat_set's are not properly re-initialized when they are cleared in v1's blkcg_reset_stats(). This can lead to a kernel panic due to NULL pointer access of the blkg pointer. The missing initialization of sync is less problematic and can be a problem in a debug kernel due to missing lockdep initialization. Fix these problems by re-initializing them after memory clearing.

References

• https://git.kernel.org/stable/c/58c135513562698f222a58ba07dbdfcfb268aa0d
• https://git.kernel.org/stable/c/0561aa6033dd181594116d705c41fc16e97161a2
• https://git.kernel.org/stable/c/892faa76be894d324bf48b12a55c7af7be2bad83
• https://git.kernel.org/stable/c/b0d26283af612b9e0cc3188b0b88ad7fdea447e8
• https://git.kernel.org/stable/c/abbce7f82613ea5eeefd0fc3c1c8e449b9cef2a2
• https://git.kernel.org/stable/c/3d2af77e31ade05ff7ccc3658c3635ec1bea0979