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Subject[PATCH 4.19 258/323] erofs: fix unsafe pagevec reuse of hooked pclusters
Date
From: Gao Xiang <hsiangkao@linux.alibaba.com>

commit 86432a6dca9bed79111990851df5756d3eb5f57c upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/staging/erofs/unzip_pagevec.h | 13 ++++++++++---
drivers/staging/erofs/unzip_vle.c | 17 +++++++++--------
2 files changed, 19 insertions(+), 11 deletions(-)

--- a/drivers/staging/erofs/unzip_pagevec.h
+++ b/drivers/staging/erofs/unzip_pagevec.h
@@ -117,11 +117,18 @@ static inline void z_erofs_pagevec_ctor_
static inline bool
z_erofs_pagevec_ctor_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 (unlikely(ctor->next == NULL && 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 (unlikely(ctor->index >= ctor->nr))
z_erofs_pagevec_ctor_pagedown(ctor, false);
--- a/drivers/staging/erofs/unzip_vle.c
+++ b/drivers/staging/erofs/unzip_vle.c
@@ -228,10 +228,10 @@ static inline bool try_to_reuse_as_compr
}

/* callers must be with work->lock held */
-static int z_erofs_vle_work_add_page(
- struct z_erofs_vle_work_builder *builder,
- struct page *page,
- enum z_erofs_page_type type)
+static int z_erofs_vle_work_add_page(struct z_erofs_vle_work_builder *builder,
+ struct page *page,
+ enum z_erofs_page_type type,
+ bool pvec_safereuse)
{
int ret;

@@ -241,9 +241,9 @@ static int z_erofs_vle_work_add_page(
try_to_reuse_as_compressed_page(builder, page))
return 0;

- ret = z_erofs_pagevec_ctor_enqueue(&builder->vector, page, type);
+ ret = z_erofs_pagevec_ctor_enqueue(&builder->vector, page, type,
+ pvec_safereuse);
builder->work->vcnt += (unsigned)ret;
-
return ret ? 0 : -EAGAIN;
}

@@ -688,14 +688,15 @@ hitted:
tight &= builder_is_followed(builder);

retry:
- err = z_erofs_vle_work_add_page(builder, page, page_type);
+ err = z_erofs_vle_work_add_page(builder, page, page_type,
+ builder_is_followed(builder));
/* should allocate an additional staging page for pagevec */
if (err == -EAGAIN) {
struct page *const newpage =
__stagingpage_alloc(page_pool, GFP_NOFS);

err = z_erofs_vle_work_add_page(builder,
- newpage, Z_EROFS_PAGE_TYPE_EXCLUSIVE);
+ newpage, Z_EROFS_PAGE_TYPE_EXCLUSIVE, true);
if (likely(!err))
goto retry;
}

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