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

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Date:   Mon, 5 Dec 2022 12:38:43 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Chen Zhongjin <chenzhongjin@...wei.com>
Cc:     syzbot+6f8cd9a0155b366d227f@...kaller.appspotmail.com,
        linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        xiang@...nel.org, chao@...nel.org, huyue2@...lpad.com,
        jefflexu@...ux.alibaba.com
Subject: Re: [PATCH -next v3] erofs: Fix pcluster memleak when its block
 address is zero

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@...kaller.appspotmail.com
> Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>

Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>

Thanks,
Gao Xiang