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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: 3883a79abd ("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>
This commit is contained in:
Gao Xiang 2021-11-04 02:20:06 +08:00
parent 8bb7eca972
commit 86432a6dca
2 changed files with 17 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
fs/erofs/zdata.c
View File

@ -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 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
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 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
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;
}

13
fs/erofs/zpvec.h
View File

@ -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);