erofs: fix unsafe pagevec reuse of hooked pclusters

There are pclusters in runtime marked with Z_EROFS_PCLUSTER_TAIL
before actual I/O submission. Thus, the decompression chain can be
extended if the following pcluster chain hooks such tail pcluster.

As the related comment mentioned, if some page is made of a hooked
pcluster and another followed pcluster, it can be reused for in-place
I/O (since I/O should be submitted anyway):
 _______________________________________________________________
|  tail (partial) page |          head (partial) page           |
|_____PRIMARY_HOOKED___|____________PRIMARY_FOLLOWED____________|

However, it's by no means safe to reuse as pagevec since if such
PRIMARY_HOOKED pclusters finally move into bypass chain without I/O
submission. It's somewhat hard to reproduce with LZ4 and I just found
it (general protection fault) by ro_fsstressing a LZMA image for long
time.

I'm going to actively clean up related code together with multi-page
folio adaption in the next few months. Let's address it directly for
easier backporting for now.

Call trace for reference:
  z_erofs_decompress_pcluster+0x10a/0x8a0 [erofs]
  z_erofs_decompress_queue.isra.36+0x3c/0x60 [erofs]
  z_erofs_runqueue+0x5f3/0x840 [erofs]
  z_erofs_readahead+0x1e8/0x320 [erofs]
  read_pages+0x91/0x270
  page_cache_ra_unbounded+0x18b/0x240
  filemap_get_pages+0x10a/0x5f0
  filemap_read+0xa9/0x330
  new_sync_read+0x11b/0x1a0
  vfs_read+0xf1/0x190

Link: https://lore.kernel.org/r/20211103182006.4040-1-xiang@kernel.org
Fixes: 3883a79abd02 ("staging: erofs: introduce VLE decompression support")
Cc: <stable@vger.kernel.org> # 4.19+
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 11c7a1aaebadea4f019d4a87d8aa6c47fc12115a..eb51df4a9f770260333750c3586c9e048b2f792b 100644 (file)
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -373,8 +373,8 @@ static bool z_erofs_try_inplace_io(struct z_erofs_collector *clt,
 
 /* callers must be with collection lock held */
 static int z_erofs_attach_page(struct z_erofs_collector *clt,
-                              struct page *page,
-                              enum z_erofs_page_type type)
+                              struct page *page, enum z_erofs_page_type type,
+                              bool pvec_safereuse)
 {
        int ret;
 
@@ -384,9 +384,9 @@ static int z_erofs_attach_page(struct z_erofs_collector *clt,
            z_erofs_try_inplace_io(clt, page))
                return 0;
 
-       ret = z_erofs_pagevec_enqueue(&clt->vector, page, type);
+       ret = z_erofs_pagevec_enqueue(&clt->vector, page, type,
+                                     pvec_safereuse);
        clt->cl->vcnt += (unsigned int)ret;
-
        return ret ? 0 : -EAGAIN;
 }
 
@@ -729,7 +729,8 @@ hitted:
                tight &= (clt->mode >= COLLECT_PRIMARY_FOLLOWED);
 
 retry:
-       err = z_erofs_attach_page(clt, page, page_type);
+       err = z_erofs_attach_page(clt, page, page_type,
+                                 clt->mode >= COLLECT_PRIMARY_FOLLOWED);
        /* should allocate an additional short-lived page for pagevec */
        if (err == -EAGAIN) {
                struct page *const newpage =
@@ -737,7 +738,7 @@ retry:
 
                set_page_private(newpage, Z_EROFS_SHORTLIVED_PAGE);
                err = z_erofs_attach_page(clt, newpage,
-                                         Z_EROFS_PAGE_TYPE_EXCLUSIVE);
+                                         Z_EROFS_PAGE_TYPE_EXCLUSIVE, true);
                if (!err)
                        goto retry;
        }

diff --git a/fs/erofs/zpvec.h b/fs/erofs/zpvec.h
index dfd7fe0503bb111b1ea80c43f5cd1cc8e3ef0b71..b05464f4a80831a9a4f5bdeaed21bd6d5eae4208 100644 (file)
--- a/fs/erofs/zpvec.h
+++ b/fs/erofs/zpvec.h
@@ -106,11 +106,18 @@ static inline void z_erofs_pagevec_ctor_init(struct z_erofs_pagevec_ctor *ctor,
 
 static inline bool z_erofs_pagevec_enqueue(struct z_erofs_pagevec_ctor *ctor,
                                           struct page *page,
-                                          enum z_erofs_page_type type)
+                                          enum z_erofs_page_type type,
+                                          bool pvec_safereuse)
 {
-       if (!ctor->next && type)
-               if (ctor->index + 1 == ctor->nr)
+       if (!ctor->next) {
+               /* some pages cannot be reused as pvec safely without I/O */
+               if (type == Z_EROFS_PAGE_TYPE_EXCLUSIVE && !pvec_safereuse)
+                       type = Z_EROFS_VLE_PAGE_TYPE_TAIL_SHARED;
+
+               if (type != Z_EROFS_PAGE_TYPE_EXCLUSIVE &&
+                   ctor->index + 1 == ctor->nr)
                        return false;
+       }
 
        if (ctor->index >= ctor->nr)
                z_erofs_pagevec_ctor_pagedown(ctor, false);