linux-kernel - Re: [PATCH v2 2/2] fs: clear a UBSAN shift-out-of-bounds warning

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Message-ID: <Y3vYIyaxzdXNrFq7@gmail.com>
Date:   Mon, 21 Nov 2022 19:57:23 +0000
From:   Eric Biggers <ebiggers@...nel.org>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] fs: clear a UBSAN shift-out-of-bounds warning

On Mon, Nov 21, 2022 at 10:44:18AM +0800, Zhen Lei wrote:
> UBSAN: shift-out-of-bounds in fs/locks.c:2572:16
> left shift of 1 by 63 places cannot be represented in type 'long long int'
> 
> Switch the calculation method to type_max() can help us eliminate this
> false positive.
> 
> On the other hand, the old implementation has problems with char and
> short types, although not currently involved.
> printf("%d: %x\n", sizeof(char),  INT_LIMIT(char));
> printf("%d: %x\n", sizeof(short), INT_LIMIT(short));
> 1: ffffff7f
> 2: ffff7fff
> 
> Suggested-by: Eric Biggers <ebiggers@...nel.org>
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> ---
>  include/linux/fs.h | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index e654435f16512c1..a384741b1449457 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1131,9 +1131,8 @@ struct file_lock_context {
>  
>  /* The following constant reflects the upper bound of the file/locking space */
>  #ifndef OFFSET_MAX
> -#define INT_LIMIT(x)	(~((x)1 << (sizeof(x)*8 - 1)))
> -#define OFFSET_MAX	INT_LIMIT(loff_t)
> -#define OFFT_OFFSET_MAX	INT_LIMIT(off_t)
> +#define OFFSET_MAX	type_max(loff_t)
> +#define OFFT_OFFSET_MAX	type_max(off_t)
>  #endif
>  
>  extern void send_sigio(struct fown_struct *fown, int fd, int band);
> -- 

Reviewed-by: Eric Biggers <ebiggers@...gle.com>

- Eric