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Date:   Mon, 28 Jun 2021 08:42:17 +1000
From:   Dave Chinner <david@fromorbit.com>
To:     Wang Shilong <wangshilong1991@gmail.com>
Cc:     linux-ext4@vger.kernel.org, Wang Shilong <wshilong@ddn.com>
Subject: Re: [PATCH] ext4: forbid U32_MAX project ID
Message-ID: <20210627224217.GL2419729@dread.disaster.area>
References: <20210625124033.5639-1-wangshilong1991@gmail.com>
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On Fri, Jun 25, 2021 at 08:40:33AM -0400, Wang Shilong wrote:
> From: Wang Shilong <wshilong@ddn.com>
> 
> U32_MAX is reserved for special purpose,
> qid_has_mapping() will return false if projid is
> 4294967295, dqget() will return NULL for it.
> 
> So U32_MAX is unsupported Project ID, fix to forbid
> it.

Actually, it's INVALID_PROJID, not U32_MAX, and we already have a
check function for that:

static inline bool projid_valid(kprojid_t projid)
{
        return !projid_eq(projid, INVALID_PROJID);
}

> Signed-off-by: Wang Shilong <wshilong@ddn.com>
> ---
>  fs/ext4/ioctl.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 31627f7dc5cd..f3a8d962c291 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -744,6 +744,9 @@ int ext4_fileattr_set(struct user_namespace *mnt_userns,
>  	u32 flags = fa->flags;
>  	int err = -EOPNOTSUPP;
>  
> +	if (fa->fsx_projid >= U32_MAX)
> +		return -EINVAL;
> +

This should actually be calling qid_valid() or projid_valid(),
and it should be in generic code because multiple filesystems
support project quotas.  i.e this should be checked in
fileattr_set_prepare(), not in ext4 specific code.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com