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From: Zi Yan <ziy@nvidia.com>
To: Luis Chamberlain <mcgrof@kernel.org>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, fstests@vger.kernel.org,
 linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, willy@infradead.org,
 hare@suse.de, john.g.garry@oracle.com, p.raghav@samsung.com,
 da.gomez@samsung.com
Subject: Re: [PATCH 1/2] mm/huge_memory: skip invalid debugfs file entry for
 folio split
Date: Wed, 24 Apr 2024 21:03:51 -0400
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In-Reply-To: <20240424225449.1498244-2-mcgrof@kernel.org>
References: <20240424225449.1498244-1-mcgrof@kernel.org>
 <20240424225449.1498244-2-mcgrof@kernel.org>
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On 24 Apr 2024, at 18:54, Luis Chamberlain wrote:

> If the file entry is too long we may easily end up going out of bounds
> and crash after strsep() on sscanf(). To avoid this ensure we bound the=

> string to an expected length before we use sscanf() on it.
>
> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> ---
>  mm/huge_memory.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 9e9879d2f501..8386d24a163e 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3623,6 +3623,7 @@ static ssize_t split_huge_pages_write(struct file=
 *file, const char __user *buf,
>  		char file_path[MAX_INPUT_BUF_SZ];
>  		pgoff_t off_start =3D 0, off_end =3D 0;
>  		size_t input_len =3D strlen(input_buf);
> +		size_t max_left_over;
>
>  		tok =3D strsep(&buf, ",");
>  		if (tok) {
> @@ -3632,6 +3633,14 @@ static ssize_t split_huge_pages_write(struct fil=
e *file, const char __user *buf,
>  			goto out;
>  		}
>
> +		max_left_over =3D MAX_INPUT_BUF_SZ - strlen(file_path);
> +		if (!buf ||
> +		    strnlen(buf, max_left_over) < 7 ||

What is this magic number 7? strlen("0xN,0xN") as the minimal input strin=
g size?
Maybe use sizeof("0xN,0xN") - 1 instead?

> +		    strnlen(buf, max_left_over) > max_left_over) {
> +			ret =3D -EINVAL;
> +			goto out;
> +		}
> +
>  		ret =3D sscanf(buf, "0x%lx,0x%lx,%d", &off_start, &off_end, &new_ord=
er);
>  		if (ret !=3D 2 && ret !=3D 3) {
>  			ret =3D -EINVAL;
> -- =

> 2.43.0

Everything else looks good to me. Reviewed-by: Zi Yan <ziy@nvidia.com>

--
Best Regards,
Yan, Zi

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