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

[Gao Xiang]

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: syzbot+6f8cd9a0155b366d227f@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Chen Zhongjin <chenzhongjin@xxxxxxxxxx>

Otherwise it looks good to me,

Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>

(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