staging: erofs: avoid loop in submit chains

As reported by erofs-utils fuzzer, 2 conditions
can happen in corrupted images, which can cause
unexpected behaviors.
 - access the same pcluster one more time;
 - access the tail end pcluster again, e.g.
            _ access again (will trigger tail merging)
           |
     1 2 3 1 2             ->   1 2 3 1
     |_ tail end of the chain    \___/ (unexpected behavior)
Let's detect and avoid them now.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Link: https://lore.kernel.org/r/20190821030908.40282-1-gaoxiang25@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/erofs/zdata.c b/drivers/staging/erofs/zdata.c
index 23283c97fd3bb04cfa0c5fefd22c98690f22f8e0..4d6faaab04f54933d1f16a9ddb499f8e1d954038 100644 (file)
--- a/drivers/staging/erofs/zdata.c
+++ b/drivers/staging/erofs/zdata.c
@@ -132,7 +132,7 @@ enum z_erofs_collectmode {
 struct z_erofs_collector {
        struct z_erofs_pagevec_ctor vector;
 
-       struct z_erofs_pcluster *pcl;
+       struct z_erofs_pcluster *pcl, *tailpcl;
        struct z_erofs_collection *cl;
        struct page **compressedpages;
        z_erofs_next_pcluster_t owned_head;
@@ -353,6 +353,11 @@ static struct z_erofs_collection *cllookup(struct z_erofs_collector *clt,
                return NULL;
 
        pcl = container_of(grp, struct z_erofs_pcluster, obj);
+       if (clt->owned_head == &pcl->next || pcl == clt->tailpcl) {
+               DBG_BUGON(1);
+               erofs_workgroup_put(grp);
+               return ERR_PTR(-EFSCORRUPTED);
+       }
 
        cl = z_erofs_primarycollection(pcl);
        if (unlikely(cl->pageofs != (map->m_la & ~PAGE_MASK))) {
@@ -381,7 +386,13 @@ static struct z_erofs_collection *cllookup(struct z_erofs_collector *clt,
                }
        }
        mutex_lock(&cl->lock);
+       /* used to check tail merging loop due to corrupted images */
+       if (clt->owned_head == Z_EROFS_PCLUSTER_TAIL)
+               clt->tailpcl = pcl;
        clt->mode = try_to_claim_pcluster(pcl, &clt->owned_head);
+       /* clean tailpcl if the current owned_head is Z_EROFS_PCLUSTER_TAIL */
+       if (clt->owned_head == Z_EROFS_PCLUSTER_TAIL)
+               clt->tailpcl = NULL;
        clt->pcl = pcl;
        clt->cl = cl;
        return cl;
@@ -434,6 +445,9 @@ static struct z_erofs_collection *clregister(struct z_erofs_collector *clt,
                kmem_cache_free(pcluster_cachep, pcl);
                return ERR_PTR(-EAGAIN);
        }
+       /* used to check tail merging loop due to corrupted images */
+       if (clt->owned_head == Z_EROFS_PCLUSTER_TAIL)
+               clt->tailpcl = pcl;
        clt->owned_head = &pcl->next;
        clt->pcl = pcl;
        clt->cl = cl;