linux-kernel - Re: [PATCH] mm: Return early in truncate

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Date:   Thu, 23 Mar 2023 19:56:18 +0800
From:   mawupeng <mawupeng1@...wei.com>
To:     <akpm@...ux-foundation.org>, <willy@...radead.org>
CC:     <mawupeng1@...wei.com>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: Return early in truncate_pagecache if newsize
 overflows

Hi maintainers.

Kindly ping.

On 2023/3/6 19:33, Wupeng Ma wrote:
> From: Ma Wupeng <mawupeng1@...wei.com>
> 
> Our own test reports a UBSAN in truncate_pagecache:
> 
> UBSAN: Undefined behaviour in mm/truncate.c:788:9
> signed integer overflow:
> 9223372036854775807 + 1 cannot be represented in type 'long long int'
> 
> Call Trace:
>   truncate_pagecache+0xd4/0xe0
>   truncate_setsize+0x70/0x88
>   simple_setattr+0xdc/0x100
>   notify_change+0x654/0xb00
>   do_truncate+0x108/0x1a8
>   do_sys_ftruncate+0x2ec/0x4a0
>   __arm64_sys_ftruncate+0x5c/0x80
> 
> For huge file which pass LONG_MAX to ftruncate, truncate_pagecache() will
> be called to truncate with newsize be LONG_MAX which will lead to
> overflow for holebegin:
> 
>   loff_t holebegin = round_up(newsize, PAGE_SIZE);
> 
> Since there is no meaning to truncate a file to LONG_MAX, return here
> to avoid burn a bunch of cpu cycles.
> 
> Signed-off-by: Ma Wupeng <mawupeng1@...wei.com>
> ---
>  mm/truncate.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/truncate.c b/mm/truncate.c
> index 7b4ea4c4a46b..99b6ce2d669b 100644
> --- a/mm/truncate.c
> +++ b/mm/truncate.c
> @@ -730,6 +730,9 @@ void truncate_pagecache(struct inode *inode, loff_t newsize)
>  	struct address_space *mapping = inode->i_mapping;
>  	loff_t holebegin = round_up(newsize, PAGE_SIZE);
>  
> +	if (holebegin < 0)
> +		return;
> +
>  	/*
>  	 * unmap_mapping_range is called twice, first simply for
>  	 * efficiency so that truncate_inode_pages does fewer