linux-kernel - Re: [PATCH v2] minix: Add required sanity checking to minix_check

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Message-ID: <3zzv4o6hiluxrxf7nlbcc3fbohtwkwmnxs6aojlgicd5cwctkk@h6nj53uelusk>
Date: Tue, 9 Dec 2025 09:48:12 +0100
From: Jan Kara <jack@...e.cz>
To: Jori Koolstra <jkoolstra@...all.nl>
Cc: Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>, Mateusz Guzik <mjguzik@...il.com>, 
	Taotao Chen <chentaotao@...iglobal.com>, linux-kernel@...r.kernel.org, skhan@...uxfoundation.org, 
	syzbot+5ad0824204c7bf9b67f2@...kaller.appspotmail.com
Subject: Re: [PATCH v2] minix: Add required sanity checking to
 minix_check_superblock()

On Mon 08-12-25 16:39:47, Jori Koolstra wrote:
> The fs/minix implementation of the minix filesystem does not currently
> support any other value for s_log_zone_size than 0. This is also the
> only value supported in util-linux; see mkfs.minix.c line 511. In
> addition, this patch adds some sanity checking for the other minix
> superblock fields, and moves the minix_blocks_needed() checks for the
> zmap and imap also to minix_check_super_block().
> 
> This also closes a related syzbot bug report.
> 
> Signed-off-by: Jori Koolstra <jkoolstra@...all.nl>
> Reported-by: syzbot+5ad0824204c7bf9b67f2@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=5ad0824204c7bf9b67f2

Looks good. Feel free to add:

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

								Honza

> ---
> Changes in v2:
> - Moved the minix_blocks_needed() checks for the zmap and imap also
> to minix_check_super_block().
> ---
>  fs/minix/inode.c | 50 ++++++++++++++++++++++++++++--------------------
>  1 file changed, 29 insertions(+), 21 deletions(-)
> 
> diff --git a/fs/minix/inode.c b/fs/minix/inode.c
> index 51ea9bdc813f..c8c6b2135abe 100644
> --- a/fs/minix/inode.c
> +++ b/fs/minix/inode.c
> @@ -170,10 +170,38 @@ static int minix_reconfigure(struct fs_context *fc)
>  static bool minix_check_superblock(struct super_block *sb)
>  {
>  	struct minix_sb_info *sbi = minix_sb(sb);
> +	unsigned long block;
>  
> -	if (sbi->s_imap_blocks == 0 || sbi->s_zmap_blocks == 0)
> +	if (sbi->s_log_zone_size != 0) {
> +		printk("minix-fs error: zone size must equal block size. "
> +		       "s_log_zone_size > 0 is not supported.\n");
> +		return false;
> +	}
> +
> +	if (sbi->s_ninodes < 1 || sbi->s_firstdatazone <= 4 ||
> +	    sbi->s_firstdatazone >= sbi->s_nzones)
>  		return false;
>  
> +	/* Apparently minix can create filesystems that allocate more blocks for
> +	 * the bitmaps than needed.  We simply ignore that, but verify it didn't
> +	 * create one with not enough blocks and bail out if so.
> +	 */
> +	block = minix_blocks_needed(sbi->s_ninodes, sb->s_blocksize);
> +	if (sbi->s_imap_blocks < block) {
> +		printk("MINIX-fs: file system does not have enough "
> +		       "imap blocks allocated. Refusing to mount.\n");
> +		return false;
> +	}
> +
> +	block = minix_blocks_needed(
> +			(sbi->s_nzones - sbi->s_firstdatazone + 1),
> +			sb->s_blocksize);
> +	if (sbi->s_zmap_blocks < block) {
> +		printk("MINIX-fs: file system does not have enough "
> +		       "zmap blocks allocated. Refusing to mount.\n");
> +		return false;
> +	}
> +
>  	/*
>  	 * s_max_size must not exceed the block mapping limitation.  This check
>  	 * is only needed for V1 filesystems, since V2/V3 support an extra level
> @@ -293,26 +321,6 @@ static int minix_fill_super(struct super_block *s, struct fs_context *fc)
>  	minix_set_bit(0,sbi->s_imap[0]->b_data);
>  	minix_set_bit(0,sbi->s_zmap[0]->b_data);
>  
> -	/* Apparently minix can create filesystems that allocate more blocks for
> -	 * the bitmaps than needed.  We simply ignore that, but verify it didn't
> -	 * create one with not enough blocks and bail out if so.
> -	 */
> -	block = minix_blocks_needed(sbi->s_ninodes, s->s_blocksize);
> -	if (sbi->s_imap_blocks < block) {
> -		printk("MINIX-fs: file system does not have enough "
> -				"imap blocks allocated.  Refusing to mount.\n");
> -		goto out_no_bitmap;
> -	}
> -
> -	block = minix_blocks_needed(
> -			(sbi->s_nzones - sbi->s_firstdatazone + 1),
> -			s->s_blocksize);
> -	if (sbi->s_zmap_blocks < block) {
> -		printk("MINIX-fs: file system does not have enough "
> -				"zmap blocks allocated.  Refusing to mount.\n");
> -		goto out_no_bitmap;
> -	}
> -
>  	/* set up enough so that it can read an inode */
>  	s->s_op = &minix_sops;
>  	s->s_time_min = 0;
> -- 
> 2.51.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR