From: "yukuai (C)" <yukuai3@huawei.com>
To: Hugh Dickins <hughd@google.com>
Cc: <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
<linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
<yi.zhang@huawei.com>, <zhengbin13@huawei.com>
Subject: Re: [PATCH] mm/shmem.c: don't set 'seals' to 'F_SEAL_SEAL' in shmem_get_inode
Date: Wed, 27 Nov 2019 14:46:55 +0800 [thread overview]
Message-ID: <f4ffdbc2-6728-1838-1a82-c0de4c484a54@huawei.com> (raw)
In-Reply-To: <alpine.LSU.2.11.1911262008330.2204@eggly.anvils>
On 2019/11/27 12:24, Hugh Dickins Wrote:
> On Wed, 27 Nov 2019, yu kuai wrote:
>
>> 'seals' is set to 'F_SEAL_SEAL' in shmem_get_inode, which means "prevent
>> further seals from being set", thus sealing API will be useless and many
>> code in shmem.c will never be reached. For example:
>
> The sealing API is not useless, and that code can be reached.
>
>>
>> shmem_setattr
>> if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
>> (newsize > oldsize && (info->seals & F_SEAL_GROW)))
>> return -EPERM;
>>
>> So, initialize 'seals' to zero is more reasonable.
>>
>> Signed-off-by: yu kuai <yukuai3@huawei.com>
>
> NAK.
>
> See memfd_create in mm/memfd.c (code which originated in mm/shmem.c,
> then was extended to support hugetlbfs also): sealing is for memfds,
> not for tmpfs or hugetlbfs files or SHM. Without thinking about it too
> hard, I believe that to allow sealing on tmpfs files would introduce
> surprising new behaviors on them, which might well raise security issues;
> and also be incompatible with the guarantees intended by sealing.
Thank you for your response.
Yu Kuai
prev parent reply other threads:[~2019-11-27 6:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-27 4:00 [PATCH] mm/shmem.c: don't set 'seals' to 'F_SEAL_SEAL' in shmem_get_inode yu kuai
2019-11-27 4:24 ` Hugh Dickins
2019-11-27 6:46 ` yukuai (C) [this message]
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