linux-ext4 - Re: [PATCH] ext4: fix integer overflow when calculating commit interval

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Date:   Mon, 26 Aug 2019 17:30:14 +0200
From:   Jan Kara <jack@...e.cz>
To:     "zhangyi (F)" <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz,
        adilger.kernel@...ger.ca
Subject: Re: [PATCH] ext4: fix integer overflow when calculating commit
 interval

On Mon 26-08-19 22:35:47, zhangyi (F) wrote:
> If user specify a large enough value of "commit=" option, it may trigger
> signed integer overflow which may lead to sbi->s_commit_interval becomes
> a large or small value, zero in particular.
> 
> UBSAN: Undefined behaviour in ../fs/ext4/super.c:1592:31
> signed integer overflow:
> 536870912 * 1000 cannot be represented in type 'int'
> [...]
> Call trace:
> [...]
> [<ffffff9008a2d120>] ubsan_epilogue+0x34/0x9c lib/ubsan.c:166
> [<ffffff9008a2d8b8>] handle_overflow+0x228/0x280 lib/ubsan.c:197
> [<ffffff9008a2d95c>] __ubsan_handle_mul_overflow+0x4c/0x68 lib/ubsan.c:218
> [<ffffff90086d070c>] handle_mount_opt fs/ext4/super.c:1592 [inline]
> [<ffffff90086d070c>] parse_options+0x1724/0x1a40 fs/ext4/super.c:1773
> [<ffffff90086d51c4>] ext4_remount+0x2ec/0x14a0 fs/ext4/super.c:4834
> [...]
> 
> Although it is not a big deal, still silence the UBSAN by limit the
> input value.
> 
> Signed-off-by: zhangyi (F) <yi.zhang@...wei.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/super.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 4079605d437a..7310facffa9d 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1874,6 +1874,13 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
>  	} else if (token == Opt_commit) {
>  		if (arg == 0)
>  			arg = JBD2_DEFAULT_MAX_COMMIT_AGE;
> +		else if (arg > INT_MAX / HZ) {
> +			ext4_msg(sb, KERN_ERR,
> +				 "Invalid commit interval %d, "
> +				 "must be smaller than %d",
> +				 arg, INT_MAX / HZ);
> +			return -1;
> +		}
>  		sbi->s_commit_interval = HZ * arg;
>  	} else if (token == Opt_debug_want_extra_isize) {
>  		sbi->s_want_extra_isize = arg;
> -- 
> 2.23.0.rc2.8.gff66981
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR