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

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Message-ID: <1956578351.2530481.1766258453335@kpc.webmail.kpnmail.nl>
Date: Sat, 20 Dec 2025 20:20:53 +0100 (CET)
From: Jori Koolstra <jkoolstra@...all.nl>
To: Christian Brauner <brauner@...nel.org>
Cc: 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()

Thanks for your time and the review Jan.

If someone has time to pull this and https://lkml.org/lkml/2025/12/1/726 in
that would be much appreciated, if there is no further critique :)

Thanks and happy holidays,
Jori.

> Op 09-12-2025 09:48 CET schreef Jan Kara <jack@...e.cz>:
> 
>  
> 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