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blk-cgroup: Fix UAF in blkcg_activate_policy() by using blkg_tryget() #837

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blk-cgroup: Fix UAF in blkcg_activate_policy() by using blkg_tryget() #837

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7 changes: 6 additions & 1 deletion block/blk-cgroup.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1621,6 +1621,10 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol)
if (blkg->pd[pol->plid])
continue;

/* a destroyed blkg may still be on q->blkg_list; skip it via tryget */
if (!blkg_tryget(blkg))
continue;

/* If prealloc matches, use it; otherwise try GFP_NOWAIT */
if (blkg == pinned_blkg) {
pd = pd_prealloc;
Expand All @@ -1637,7 +1641,6 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol)
*/
if (pinned_blkg)
blkg_put(pinned_blkg);
blkg_get(blkg);
pinned_blkg = blkg;

spin_unlock_irq(&q->queue_lock);
Expand Down Expand Up @@ -1666,6 +1669,8 @@ int blkcg_activate_policy(struct gendisk *disk, const struct blkcg_policy *pol)
pd->online = true;

spin_unlock(&blkg->blkcg->lock);

blkg_put(blkg);
}

__set_bit(pol->plid, q->blkcg_pols);
Expand Down