Re: [PATCH] block: Check blkg_to_lat return value to avoid NULL dereference

On 12.02.25 09:32, Wentao Liang wrote:

The function blkg_to_lat() may return NULL if the blkg is not associated with an iolatency group. In iolatency_set_min_lat_nsec() and iolatency_pd_init(), the return values are not checked, leading to potential NULL pointer dereferences.

This patch adds checks for the return values of blkg_to_lat and let it returns early if it is NULL, preventing the NULL pointer dereference.

Fixes: d70675121546 ("block: introduce blk-iolatency io controller") Cc: stable@vger.kernel.org # 4.19+ Signed-off-by: Wentao Liang vulab@iscas.ac.cn

---

block/blk-iolatency.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c index ebb522788d97..398f0a1747c4 100644 --- a/block/blk-iolatency.c +++ b/block/blk-iolatency.c @@ -787,6 +787,8 @@ static int blk_iolatency_init(struct gendisk *disk) static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) { struct iolatency_grp *iolat = blkg_to_lat(blkg);

• if (!iolat)

• return;
  

  struct blk_iolatency *blkiolat = iolat->blkiolat; u64 oldval = iolat->min_lat_nsec;

Uh that looks horrible. I haven't checked the surrounding code but please please at least make it

static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) { struct iolatency_grp *iolat = blkg_to_lat(blkg); struct blk_iolatency *blkiolat; u64 oldval;

if (!iolat) return;

blkiolat = iolat->blkiolat; oldval = iolat->min_lat_nsec;

@@ -1013,6 +1015,8 @@ static void iolatency_pd_init(struct blkg_policy_data *pd) */ if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) { struct iolatency_grp *parent = blkg_to_lat(blkg->parent);

• if (!parent)
  

• 	return;
  

  atomic_set(&iolat->scale_cookie, atomic_read(&parent->child_lat.scale_cookie)); } else {