2019-08-19 10:36:35

by Gao Xiang

Subject: [PATCH 4/6] 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.

Signed-off-by: Gao Xiang <[email protected]>
---
drivers/staging/erofs/zdata.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/erofs/zdata.c b/drivers/staging/erofs/zdata.c
index 23283c97fd3b..aae2f2b8353f 100644
--- 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))) {
@@ -381,6 +386,9 @@ 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);
clt->pcl = pcl;
clt->cl = cl;
@@ -434,6 +442,9 @@ 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;
--
2.17.1

2019-08-19 14:51:32

by Chao Yu

Subject: Re: [PATCH 4/6] staging: erofs: avoid loop in submit chains

On 2019-8-19 18:34, Gao Xiang wrote:
> 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.
>
> Signed-off-by: Gao Xiang <[email protected]>

Reviewed-by: Chao Yu <[email protected]>

Thanks,