2022-03-22 08:20:49

by Xiaoke Wang

Subject: [PATCH] erofs: fix a potential NULL dereference of alloc_pages()

From: Xiaoke Wang <[email protected]>

alloc_pages() returns the page on success or NULL if allocation fails,
while set_page_private() will dereference `newpage`. So it is better to
catch the memory error in case other errors happen.

Signed-off-by: Xiaoke Wang <[email protected]>
---
fs/erofs/zdata.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 11c7a1a..36a5421 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -735,11 +735,15 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
struct page *const newpage =
alloc_page(GFP_NOFS | __GFP_NOFAIL);

- set_page_private(newpage, Z_EROFS_SHORTLIVED_PAGE);
- err = z_erofs_attach_page(clt, newpage,
- Z_EROFS_PAGE_TYPE_EXCLUSIVE);
- if (!err)
- goto retry;
+ if (!newpage) {
+ err = -ENOMEM;
+ } else {
+ set_page_private(newpage, Z_EROFS_SHORTLIVED_PAGE);
+ err = z_erofs_attach_page(clt, newpage,
+ Z_EROFS_PAGE_TYPE_EXCLUSIVE);
+ if (!err)
+ goto retry;
+ }
}

if (err)
--

2022-03-22 10:41:30

by Gao Xiang

Subject: Re: [PATCH] erofs: fix a potential NULL dereference of alloc_pages()

On Tue, Mar 22, 2022 at 04:08:12PM +0800, [email protected] wrote:
> From: Xiaoke Wang <[email protected]>
>
> alloc_pages() returns the page on success or NULL if allocation fails,
> while set_page_private() will dereference `newpage`. So it is better to
> catch the memory error in case other errors happen.
>
> Signed-off-by: Xiaoke Wang <[email protected]>
> ---
> fs/erofs/zdata.c | 14 +++++++++-----
> 1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index 11c7a1a..36a5421 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -735,11 +735,15 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
> struct page *const newpage =
> alloc_page(GFP_NOFS | __GFP_NOFAIL);
>

It's really a nofail allocation, am I missing something?

Thanks,
Gao Xiang

> - set_page_private(newpage, Z_EROFS_SHORTLIVED_PAGE);
> - err = z_erofs_attach_page(clt, newpage,
> - Z_EROFS_PAGE_TYPE_EXCLUSIVE);
> - if (!err)
> - goto retry;
> + if (!newpage) {
> + err = -ENOMEM;
> + } else {
> + set_page_private(newpage, Z_EROFS_SHORTLIVED_PAGE);
> + err = z_erofs_attach_page(clt, newpage,
> + Z_EROFS_PAGE_TYPE_EXCLUSIVE);
> + if (!err)
> + goto retry;
> + }
> }
>
> if (err)
> --

2022-03-22 10:52:47

by Xiaoke Wang

Subject: Re: [PATCH] erofs: fix a potential NULL dereference of alloc_pages()

On Tue, 22 Mar 2022 16:28:09 +0800, [email protected] wrote:

&gt; It's really a nofail allocation, am I missing something?

Sorry, I did not carefully notice the flag `__GFP_NOFAIL`.
Please ignore this patch if this does not need to deal with failure.

Regards,
Xiaoke Wang