[PATCH 5.0 19/25] staging: erofs: compressed_pages should not be accessed again after freed

Greg Kroah-Hartman
2019-03-12T17:11:48Z

From: Gao Xiang <gaoxiang25@huawei.com>

commit af692e117cb8cd9d3d844d413095775abc1217f9 upstream.

This patch resolves the following page use-after-free issue,
z_erofs_vle_unzip:
...
for (i = 0; i < nr_pages; ++i) {
...
z_erofs_onlinepage_endio(page); (1)
}

for (i = 0; i < clusterpages; ++i) {
page = compressed_pages[i];

if (page->mapping == mngda) (2)
continue;
/* recycle all individual staging pages */
(void)z_erofs_gather_if_stagingpage(page_pool, page); (3)
WRITE_ONCE(compressed_pages[i], NULL);
}
...

After (1) is executed, page is freed and could be then reused, if
compressed_pages is scanned after that, it could fall info (2) or
(3) by mistake and that could finally be in a mess.

This patch aims to solve the above issue only with little changes
as much as possible in order to make the fix backport easier.

Fixes: 3883a79abd02 ("staging: erofs: introduce VLE decompression support")
Cc: <stable@vger.kernel.org> # 4.19+
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/staging/erofs/unzip_vle.c | 38 +++++++++++++++++-----------------
drivers/staging/erofs/unzip_vle.h | 3 --
drivers/staging/erofs/unzip_vle_lz4.c | 19 +++++++----------
3 files changed, 29 insertions(+), 31 deletions(-)

--- a/drivers/staging/erofs/unzip_vle.c
+++ b/drivers/staging/erofs/unzip_vle.c
@@ -1017,11 +1017,10 @@ repeat:
if (llen > grp->llen)
llen = grp->llen;

- err = z_erofs_vle_unzip_fast_percpu(compressed_pages,
- clusterpages, pages, llen, work->pageofs,
- z_erofs_onlinepage_endio);
+ err = z_erofs_vle_unzip_fast_percpu(compressed_pages, clusterpages,
+ pages, llen, work->pageofs);
if (err != -ENOTSUPP)
- goto out_percpu;
+ goto out;

if (sparsemem_pages >= nr_pages)
goto skip_allocpage;
@@ -1042,8 +1041,25 @@ skip_allocpage:
erofs_vunmap(vout, nr_pages);

out:
+ /* must handle all compressed pages before endding pages */
+ for (i = 0; i < clusterpages; ++i) {
+ page = compressed_pages[i];
+
+#ifdef EROFS_FS_HAS_MANAGED_CACHE
+ if (page->mapping == MNGD_MAPPING(sbi))
+ continue;
+#endif
+ /* recycle all individual staging pages */
+ (void)z_erofs_gather_if_stagingpage(page_pool, page);
+
+ WRITE_ONCE(compressed_pages[i], NULL);
+ }
+
for (i = 0; i < nr_pages; ++i) {
page = pages[i];
+ if (!page)
+ continue;
+
DBG_BUGON(!page->mapping);

/* recycle all individual staging pages */
@@ -1056,20 +1072,6 @@ out:
z_erofs_onlinepage_endio(page);
}

-out_percpu:
- for (i = 0; i < clusterpages; ++i) {
- page = compressed_pages[i];
-
-#ifdef EROFS_FS_HAS_MANAGED_CACHE
- if (page->mapping == MNGD_MAPPING(sbi))
- continue;
-#endif
- /* recycle all individual staging pages */
- (void)z_erofs_gather_if_stagingpage(page_pool, page);
-
- WRITE_ONCE(compressed_pages[i], NULL);
- }
-
if (pages == z_pagemap_global)
mutex_unlock(&z_pagemap_global_lock);
else if (unlikely(pages != pages_onstack))
--- a/drivers/staging/erofs/unzip_vle.h
+++ b/drivers/staging/erofs/unzip_vle.h
@@ -218,8 +218,7 @@ extern int z_erofs_vle_plain_copy(struct

extern int z_erofs_vle_unzip_fast_percpu(struct page **compressed_pages,
unsigned clusterpages, struct page **pages,
- unsigned outlen, unsigned short pageofs,
- void (*endio)(struct page *));
+ unsigned int outlen, unsigned short pageofs);

extern int z_erofs_vle_unzip_vmap(struct page **compressed_pages,
unsigned clusterpages, void *vaddr, unsigned llen,
--- a/drivers/staging/erofs/unzip_vle_lz4.c
+++ b/drivers/staging/erofs/unzip_vle_lz4.c
@@ -125,8 +125,7 @@ int z_erofs_vle_unzip_fast_percpu(struct
unsigned int clusterpages,
struct page **pages,
unsigned int outlen,
- unsigned short pageofs,
- void (*endio)(struct page *))
+ unsigned short pageofs)
{
void *vin, *vout;
unsigned int nr_pages, i, j;
@@ -148,19 +147,16 @@ int z_erofs_vle_unzip_fast_percpu(struct
ret = z_erofs_unzip_lz4(vin, vout + pageofs,
clusterpages * PAGE_SIZE, outlen);

- if (ret >= 0) {
- outlen = ret;
- ret = 0;
- }
+ if (ret < 0)
+ goto out;
+ ret = 0;

for (i = 0; i < nr_pages; ++i) {
j = min((unsigned int)PAGE_SIZE - pageofs, outlen);

if (pages[i]) {
- if (ret < 0) {
- SetPageError(pages[i]);
- } else if (clusterpages == 1 &&
- pages[i] == compressed_pages[0]) {
+ if (clusterpages == 1 &&
+ pages[i] == compressed_pages[0]) {
memcpy(vin + pageofs, vout + pageofs, j);
} else {
void *dst = kmap_atomic(pages[i]);
@@ -168,12 +164,13 @@ int z_erofs_vle_unzip_fast_percpu(struct
memcpy(dst + pageofs, vout + pageofs, j);
kunmap_atomic(dst);
}
- endio(pages[i]);
}
vout += PAGE_SIZE;
outlen -= j;
pageofs = 0;
}
+
+out:
preempt_enable();

if (clusterpages == 1)