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

[Chao Yu]

On 2022/12/5 14:08, Gao Xiang wrote:
> Hi all,
>
> 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>
> > ---
> > v1 -> v2:
> > As Gao's advice, we should fail to register pcluster if m_pa is zero.
> > Maked it this way and changed the commit message.
> >
> > v2 -> v3:
> > Slightly fix commit message and add -next tag.
>
> I've updated the patch itself as below
> (Since we only need to fail out for non-tailpacking cases, tailpacking
>   inline inodes could still have m_pa < EROFS_BLKSIZ):
>
>  From f5e037e760d338ca0c116e507be663cb843d42f0 Mon Sep 17 00:00:00 2001
> From: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
> Date: Mon, 5 Dec 2022 11:49:57 +0800
> Subject: [PATCH] erofs: Fix pcluster memleak when its block address 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 the block address of a non-inlined 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: Yue Hu <huyue2@xxxxxxxxxxx>
> Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

Reviewed-by: Chao Yu <chao@xxxxxxxxxx>

Thanks,