Re: [PATCH] erofs: Fix pcluster become inline when m_pa is zero

[Chen Zhongjin]

Hi,

On 2022/12/3 21:40, Gao Xiang wrote:
> On Sat, Dec 03, 2022 at 09:20:17PM +0800, Gao Xiang wrote:
> > Hi Zhongjin,
> >
> > On Sat, Dec 03, 2022 at 05:45:27PM +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
> > > become zero although pcl is not an inline pcluster.
> > Thanks for the patch!
> >
> > We should just fail out if map->m_pa / EROFS_BLKSIZ == 0.
> >
> > > Then following path adds refcount for grp, but the it won't be put
> > > because pcl is inline, which makes pcl not released when shrink.
> > >
> > > z_erofs_readahead()
> > >    z_erofs_do_read_page() # for another page
> > >      z_erofs_collector_begin()
> > >        erofs_find_workgroup()
> > >          erofs_workgroup_get()
> > >
> > > To fix this, add an attribute in z_erofs_pcluster to mark the inline
> > > state which not depends on index of grp.
> > I think the main reason is "inline pcluster _always_ did memory leak
> > before since I don't find any chance to these free inline pclusters
> > in the current codebase.
> >
> > Actually I submitted a patch for this, could you check/review this
> > if possible?
> > https://lore.kernel.org/r/20221202033327.52702-1-hsiangkao@xxxxxxxxxxxxxxxxx
> Oh, I just realized my patch may be incorrect, I think we need to
> just fail out this (since m_pblk == 0 cannot be a real pcluster,
> since it has on-disk super block at least):
>
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index ab22100be861..e14e6c32e70d 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -496,7 +496,8 @@ 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;
>
>
> Could you resend next version behaving like the above?
Thanks for your time and review!

I just didn't know weather m_pa is legal to be zero.
I tested this and simply fail here can also solve the memleak.

Have sent v2 for this. And the title is slightly changed, see:
[PATCH v2] erofs: Fix pcluster memleak when m_pa is zero

Best,
Chen
> Thanks,
> Gao Xiang
>
> > Thanks,
> > Gao Xiang
> >
> > > Fixes: cecf864d3d76 ("erofs: support inline data decompression")
> > > Reported-by: syzbot+6f8cd9a0155b366d227f@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>
> > > ---
> > >   fs/erofs/zdata.c | 2 +-
> > >   fs/erofs/zdata.h | 5 ++++-
> > >   2 files changed, 5 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> > > index b792d424d774..fef2624d19e3 100644
> > > --- a/fs/erofs/zdata.c
> > > +++ b/fs/erofs/zdata.c
> > > @@ -517,7 +517,7 @@ static int z_erofs_register_pcluster(struct z_erofs_decompress_frontend *fe)
> > >   	DBG_BUGON(!mutex_trylock(&pcl->lock));
> > >   
> > >   	if (ztailpacking) {
> > > -		pcl->obj.index = 0;	/* which indicates ztailpacking */
> > > +		pcl->is_inline = true;  /* which indicates ztailpacking */
> > >   		pcl->pageofs_in = erofs_blkoff(map->m_pa);
> > >   		pcl->tailpacking_size = map->m_plen;
> > >   	} else {
> > > diff --git a/fs/erofs/zdata.h b/fs/erofs/zdata.h
> > > index d98c95212985..35051ad27521 100644
> > > --- a/fs/erofs/zdata.h
> > > +++ b/fs/erofs/zdata.h
> > > @@ -78,6 +78,9 @@ struct z_erofs_pcluster {
> > >   		unsigned short tailpacking_size;
> > >   	};
> > >   
> > > +	/* I:  whether it is inline or not */
> > > +	bool is_inline;
> > > +
> > >   	/* I: compression algorithm format */
> > >   	unsigned char algorithmformat;
> > >   
> > > @@ -115,7 +118,7 @@ struct z_erofs_decompressqueue {
> > >   
> > >   static inline bool z_erofs_is_inline_pcluster(struct z_erofs_pcluster *pcl)
> > >   {
> > > -	return !pcl->obj.index;
> > > +	return pcl->is_inline;
> > >   }
> > >   
> > >   static inline unsigned int z_erofs_pclusterpages(struct z_erofs_pcluster *pcl)
> > > --
> > > 2.17.1