linux-kernel - Re: [PATCH v2] fs: minix: Fix handling of corrupted directories

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Message-ID: <s5pju6jp2k4ddyuuz2xydeys5lhashkbvwa2lmtw3dmtedupw5@sjdrgnhwsvza>
Date: Wed, 14 May 2025 17:54:03 +0200
From: Jan Kara <jack@...e.cz>
To: Andrey Kriulin <kitotavrik.s@...il.com>
Cc: Christian Brauner <brauner@...nel.org>, 
	"Matthew Wilcox (Oracle)" <willy@...radead.org>, Josef Bacik <josef@...icpanda.com>, NeilBrown <neilb@...e.de>, 
	Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org, 
	stable@...r.kernel.org, Andrey Kriulin <kitotavrik.media@...il.com>
Subject: Re: [PATCH v2] fs: minix: Fix handling of corrupted directories

On Wed 14-05-25 13:38:35, Andrey Kriulin wrote:
> If the directory is corrupted and the number of nlinks is less than 2
> (valid nlinks have at least 2), then when the directory is deleted, the
> minix_rmdir will try to reduce the nlinks(unsigned int) to a negative
> value.
> 
> Make nlinks validity check for directory.
> 
> Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@...r.kernel.org
> Signed-off-by: Andrey Kriulin <kitotavrik.media@...il.com>
> Signed-off-by: Andrey Kriulin <kitotavrik.s@...il.com>
> ---
> v2: Move nlinks validaty check to V[12]_minix_iget() per Jan Kara
> <jack@...e.cz> request. Change return error code to EUCLEAN. Don't block
> directory in r/o mode per Al Viro <viro@...iv.linux.org.uk> request.
> 
>  fs/minix/inode.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> diff --git a/fs/minix/inode.c b/fs/minix/inode.c
> index f007e389d5d2..d815397b8b0d 100644
> --- a/fs/minix/inode.c
> +++ b/fs/minix/inode.c
> @@ -517,6 +517,14 @@ static struct inode *V1_minix_iget(struct inode *inode)
>  		iget_failed(inode);
>  		return ERR_PTR(-ESTALE);
>  	}
> +	if (S_ISDIR(raw_inode->i_mode) && raw_inode->i_nlinks < 2) {
> +		printk("MINIX-fs: inode directory with corrupted number of links");

A message like this is rather useless because it shows nothing either about
the inode or the link count or the filesystem where this happened. I'd
either improve or delete it.

> +		if (!sb_rdonly(inode->i_sb)) {
> +			brelse(bh);
> +			iget_failed(inode);
> +			return ERR_PTR(-EUCLEAN);
> +		}

OK, but when the inode is cached in memory with the wrong link count and
then the filesystem is remounted read-write, you will get the same problem
as before? I guess the easiest is to fudge i_nlinks count in memory to 2 to
avoid issues...


								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR