Re: [PATCH AUTOSEL 4.20 35/81] debugfs: debugfs_lookup() should return NULL if not found

[Greg Kroah-Hartman]

On Thu, Feb 28, 2019 at 10:07:27AM -0500, Sasha Levin wrote:
> From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> 
> [ Upstream commit 37ea7b630ae5cdea4e8ff381d9d23abfef5939e6 ]
> 
> Lots of callers of debugfs_lookup() were just checking NULL to see if
> the file/directory was found or not.  By changing this in ff9fb72bc077
> ("debugfs: return error values, not NULL") we caused some subsystems to
> easily crash.
> 
> Fixes: ff9fb72bc077 ("debugfs: return error values, not NULL")
> Reported-by: syzbot+b382ba6a802a3d242790@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Omar Sandoval <osandov@xxxxxx>
> Cc: Jens Axboe <axboe@xxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  fs/debugfs/inode.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> index b16f8035b1af7..29c68c5d44d5f 100644
> --- a/fs/debugfs/inode.c
> +++ b/fs/debugfs/inode.c
> @@ -254,8 +254,8 @@ MODULE_ALIAS_FS("debugfs");
>   * @parent: a pointer to the parent dentry of the file.
>   *
>   * This function will return a pointer to a dentry if it succeeds.  If the file
> - * doesn't exist or an error occurs, %ERR_PTR(-ERROR) will be returned.  The
> - * returned dentry must be passed to dput() when it is no longer needed.
> + * doesn't exist or an error occurs, %NULL will be returned.  The returned
> + * dentry must be passed to dput() when it is no longer needed.
>   *
>   * If debugfs is not enabled in the kernel, the value -%ENODEV will be
>   * returned.
> @@ -265,17 +265,17 @@ struct dentry *debugfs_lookup(const char *name, struct dentry *parent)
>  	struct dentry *dentry;
>  
>  	if (IS_ERR(parent))
> -		return parent;
> +		return NULL;
>  
>  	if (!parent)
>  		parent = debugfs_mount->mnt_root;
>  
>  	dentry = lookup_one_len_unlocked(name, parent, strlen(name));
>  	if (IS_ERR(dentry))
> -		return dentry;
> +		return NULL;
>  	if (!d_really_is_positive(dentry)) {
>  		dput(dentry);
> -		return ERR_PTR(-EINVAL);
> +		return NULL;
>  	}
>  	return dentry;

As the "Fixes:" commit should not be backported, no need for this one
either.  Please drop from all queues.

thanks,

greg k-h