linux-kernel - Re: [PATCH][next][V2] fs/jfs: fix potential integer overflow on shift of a int

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Message-ID: <5225934e-c3ea-9481-ba66-5a70dca8ba53@oracle.com>
Date:   Thu, 11 Feb 2021 11:49:59 -0600
From:   Dave Kleikamp <dave.kleikamp@...cle.com>
To:     Colin King <colin.king@...onical.com>,
        jfs-discussion@...ts.sourceforge.net
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next][V2] fs/jfs: fix potential integer overflow on shift
 of a int

On 2/11/21 7:01 AM, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The left shift of int 32 bit integer constant 1 is evaluated using 32 bit
> arithmetic and then assigned to a signed 64 bit integer. In the case where
> l2nb is 32 or more this can lead to an overflow.  Avoid this by shifting
> the value 1LL instead.
> 
> Addresses-Coverity: ("Uninitentional integer overflow")
> Fixes: b40c2e665cd5 ("fs/jfs: TRIM support for JFS Filesystem")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>

Looks good. I'll include it in the next jfs drop.

Thanks,
Shaggy

> ---
> 
> V2: shift 1LL rather than using BIT_ULL macro as suggested by
>      Dave Kleikamp.
> 
> ---
>   fs/jfs/jfs_dmap.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> index 94b7c1cb5ceb..7aee15608619 100644
> --- a/fs/jfs/jfs_dmap.c
> +++ b/fs/jfs/jfs_dmap.c
> @@ -1656,7 +1656,7 @@ s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen)
>   		} else if (rc == -ENOSPC) {
>   			/* search for next smaller log2 block */
>   			l2nb = BLKSTOL2(nblocks) - 1;
> -			nblocks = 1 << l2nb;
> +			nblocks = 1LL << l2nb;
>   		} else {
>   			/* Trim any already allocated blocks */
>   			jfs_error(bmp->db_ipbmap->i_sb, "-EIO\n");
>