[PATCH 5.10.y] blk-cgroup: Reinit blkg_iostat_set after clearing in blkcg_reset_stats()

[Vasiliy Kovalev <kovalev@altlinux.org>]

From: Waiman Long <longman@redhat.com>

[ Upstream commit 3d2af77e31ade05ff7ccc3658c3635ec1bea0979 ]

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.

Fixes: 3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()")
Fixes: f73316482977 ("blk-cgroup: reimplement basic IO stats using cgroup rstat")
Signed-off-by: Waiman Long <longman@redhat.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230606180724.2455066-1-longman@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
[ Remove this line: bis -> blkg = blkg for blkg was introduced by commit
  3b8cc6298724 ("blk-cgroup: Optimize blkcg_rstat_flush()") since v6.2. ]
Signed-off-by: Alva Lan <alvalan9@foxmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 0561aa6033dd181594116d705c41fc16e97161a2)
[ kovalev: bp to fix CVE-2023-53421 ]
Signed-off-by: Vasiliy Kovalev <kovalev@altlinux.org>
---
 block/blk-cgroup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index dbd18b75ec91..7ffdc3360a6c 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -464,8 +464,12 @@ static int blkcg_reset_stats(struct cgroup_subsys_state *css,
 			struct blkg_iostat_set *bis =
 				per_cpu_ptr(blkg->iostat_cpu, cpu);
 			memset(bis, 0, sizeof(*bis));
+
+			/* Re-initialize the cleared blkg_iostat_set */
+			u64_stats_init(&bis->sync);
 		}
 		memset(&blkg->iostat, 0, sizeof(blkg->iostat));
+		u64_stats_init(&blkg->iostat.sync);
 
 		for (i = 0; i < BLKCG_MAX_POLS; i++) {
 			struct blkcg_policy *pol = blkcg_policy[i];
-- 
2.50.1