Re: [PATCH -next v3] erofs: Fix pcluster memleak when its block address is zero

From: Gao Xiang
Date: Sun Dec 04 2022 - 23:38:56 EST


On Mon, Dec 05, 2022 at 11:49:57AM +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 the block address of a pcluster to be zero, add
> check here to avoid registering the pcluster which would be leaked.
>
> Fixes: cecf864d3d76 ("erofs: support inline data decompression")
> Reported-by: syzbot+6f8cd9a0155b366d227f@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>

Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

Thanks,
Gao Xiang