2022-12-05 02:03:25

by Chen Zhongjin

Subject: [PATCH v2] erofs: Fix pcluster memleak when m_pa is zero

syzkaller reported a memleak:
https://syzkaller.appspot.com/bug?id=62f37ff612f0021641eda5b17f056f1668aa9aed

unreferenced object 0xffff88811009c7f8 (size 136):
...
backtrace:
[<ffffffff821db19b>] z_erofs_do_read_page+0x99b/0x1740
[<ffffffff821dee9e>] z_erofs_readahead+0x24e/0x580
[<ffffffff814bc0d6>] read_pages+0x86/0x3d0
...

syzkaller constructed a case: in z_erofs_register_pcluster(),
ztailpacking = false and map->m_pa = zero. This makes pcl->obj.index be
zero although pcl is not a inline pcluster.

Then following path adds refcount for grp, but the refcount won't be put
because pcl is inline.

z_erofs_readahead()
z_erofs_do_read_page() # for another page
z_erofs_collector_begin()
erofs_find_workgroup()
erofs_workgroup_get()

Since it's illegal for map->m_pa to be zero, add check here to avoid
registering the pcluster which would be leaked.

Fixes: cecf864d3d76 ("erofs: support inline data decompression")
Reported-by: [email protected]
Signed-off-by: Chen Zhongjin <[email protected]>
---
As Gao's advice, we should fail to register pcluster if m_pa is zero.
Maked it this way and changed the commit message.
---
fs/erofs/zdata.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index b792d424d774..7826634f4f51 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -488,7 +488,8 @@ static int z_erofs_register_pcluster(struct z_erofs_decompress_frontend *fe)
struct erofs_workgroup *grp;
int err;

- if (!(map->m_flags & EROFS_MAP_ENCODED)) {
+ if (!(map->m_flags & EROFS_MAP_ENCODED) ||
+ !(map->m_pa >> PAGE_SHIFT)) {
DBG_BUGON(1);
return -EFSCORRUPTED;
}
--
2.17.1

2022-12-05 04:33:32

by Gao Xiang

Subject: Re: [PATCH v2] erofs: Fix pcluster memleak when m_pa is zero

On Mon, Dec 05, 2022 at 09:50:24AM +0800, Chen Zhongjin wrote:
> syzkaller reported a memleak:
> https://syzkaller.appspot.com/bug?id=62f37ff612f0021641eda5b17f056f1668aa9aed
>
> unreferenced object 0xffff88811009c7f8 (size 136):
> ...
> backtrace:
> [<ffffffff821db19b>] z_erofs_do_read_page+0x99b/0x1740
> [<ffffffff821dee9e>] z_erofs_readahead+0x24e/0x580
> [<ffffffff814bc0d6>] read_pages+0x86/0x3d0
> ...
>
> syzkaller constructed a case: in z_erofs_register_pcluster(),
> ztailpacking = false and map->m_pa = zero. This makes pcl->obj.index be
> zero although pcl is not a inline pcluster.
>
> Then following path adds refcount for grp, but the refcount won't be put
> because pcl is inline.
>
> z_erofs_readahead()
> z_erofs_do_read_page() # for another page
> z_erofs_collector_begin()
> erofs_find_workgroup()
> erofs_workgroup_get()
>
> Since it's illegal for map->m_pa to be zero, add check here to avoid

the block address of a pcluster to be zero,

not just map->m_pa == 0.

Also subject line needs to be updated as well,
"Fix pcluster memleak when its block address is zero"

> registering the pcluster which would be leaked.
>
> Fixes: cecf864d3d76 ("erofs: support inline data decompression")
> Reported-by: [email protected]
> Signed-off-by: Chen Zhongjin <[email protected]>

Otherwise it looks good to me,

Reviewed-by: Gao Xiang <[email protected]>

(Would you mind sending a next version for this so I can apply it?)

Thanks,
Gao Xiang

> ---
> As Gao's advice, we should fail to register pcluster if m_pa is zero.
> Maked it this way and changed the commit message.
> ---
> fs/erofs/zdata.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index b792d424d774..7826634f4f51 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -488,7 +488,8 @@ static int z_erofs_register_pcluster(struct z_erofs_decompress_frontend *fe)
> struct erofs_workgroup *grp;
> int err;
>
> - if (!(map->m_flags & EROFS_MAP_ENCODED)) {
> + if (!(map->m_flags & EROFS_MAP_ENCODED) ||
> + !(map->m_pa >> PAGE_SHIFT)) {
> DBG_BUGON(1);
> return -EFSCORRUPTED;
> }
> --
> 2.17.1