linux-kernel - Re: [PATCH v3] fs: minix: Fix handling of corrupted directories

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Message-ID: <enhxf3daymfubn226ha4ywvh74k3zhacdya2mgfln7g2kzsq6x@llwzvp3vejsk>
Date: Fri, 16 May 2025 12:22:53 +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
Subject: Re: [PATCH v3] fs: minix: Fix handling of corrupted directories

On Thu 15-05-25 20:54:57, 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 directories.
> 
> 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.s@...il.com>

This patch is mostly fine (see just one nit below).

> ---
> v3: Move nlinks validaty check to minix_rmdir and minix_rename per Jan
> Kara <jack@...e.cz> request.
> 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/namei.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/minix/namei.c b/fs/minix/namei.c
> index 8938536d8d3c..5a1e5f8ef443 100644
> --- a/fs/minix/namei.c
> +++ b/fs/minix/namei.c
> @@ -161,8 +161,12 @@ static int minix_unlink(struct inode * dir, struct dentry *dentry)
>  static int minix_rmdir(struct inode * dir, struct dentry *dentry)
>  {
>  	struct inode * inode = d_inode(dentry);
> -	int err = -ENOTEMPTY;
> +	int err = -EUCLEAN;
>  
> +	if (inode->i_nlink < 2)

This should be <= 2 as well?

								Honza

> +		return err;
> +
> +	err = -ENOTEMPTY;
>  	if (minix_empty_dir(inode)) {
>  		err = minix_unlink(dir, dentry);
>  		if (!err) {
> @@ -235,6 +239,10 @@ static int minix_rename(struct mnt_idmap *idmap,
>  	mark_inode_dirty(old_inode);
>  
>  	if (dir_de) {
> +		if (old_dir->i_nlink <= 2) {
> +			err = -EUCLEAN;
> +			goto out_dir;
> +		}
>  		err = minix_set_link(dir_de, dir_folio, new_dir);
>  		if (!err)
>  			inode_dec_link_count(old_dir);
> -- 
> 2.47.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR