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Date:   Thu, 12 Jan 2023 03:43:31 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Peng Zhang <zhangpeng362@huawei.com>
Cc:     almaz.alexandrovich@paragon-software.com,
        kari.argillander@gmail.com, akpm@linux-foundation.org,
        ntfs3@lists.linux.dev, linux-kernel@vger.kernel.org,
        sunnanyong@huawei.com, wangkefeng.wang@huawei.com,
        Dan Carpenter <error27@gmail.com>
Subject: Re: [PATCH -next] fs/ntfs3: Fix potential NULL/IS_ERR bug in
 ntfs_lookup()
Message-ID: <Y7+B40Mnnm7/rY+O@ZenIV>
References: <20230112013248.2464556-1-zhangpeng362@huawei.com>
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On Thu, Jan 12, 2023 at 01:32:48AM +0000, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@huawei.com>
> 
> Dan Carpenter reported a Smatch static checker warning:
> 
> fs/ntfs3/namei.c:96 ntfs_lookup()
> error: potential NULL/IS_ERR bug 'inode'
> It will cause null-ptr-deref when dir_search_u() returns NULL if the
> file is not found.
> Fix this by replacing IS_ERR() with IS_ERR_OR_NULL() to add a check for
> NULL.

That's a bad approach - you are papering over bad calling conventions instead of
fixing them.

IS_ERR_OR_NULL is almost never the right tool.  Occasionally there are valid
cases for function possibly returning pointer/NULL/ERR_PTR(...); this is
almost certainly not one of those.

Incidentally, inodes with NULL ->i_op should never exist.  _Any_ place that
sets ->i_op to NULL is broken, plain and simple.  A new instance of struct
inode has ->i_op pointing to empty method table; it *is* initialized.