linux-kernel - Re: [PATCH BUGFIX -rc6] Smackfs: remove redundant lock, fix open(,O

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Date:	Fri, 21 Mar 2008 11:17:51 -0700 (PDT)
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	"Ahmed S. Darwish" <darwish.07@...il.com>,
	Jonathan Corbet <corbet@....net>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Daniel Walker <dwalker@...sta.com>
Subject: Re: [PATCH BUGFIX -rc6] Smackfs: remove redundant lock, fix open(,O_RDWR)


--- "Ahmed S. Darwish" <darwish.07@...il.com> wrote:

> Hi all,
> 
> Older smackfs was parsing MAC rules by characters, thus a need of
> locking write sessions on open() was needed. This lock is no longer
> useful now since each rule is handled by a single write() call.
> 
> This is also a bugfix since seq_open() was not called if an open()
> O_RDWR flag was given, leading to a seq_read() without an initialized
> seq_file, thus an Oops.
> 
> Signed-off-by: Ahmed S. Darwish <darwish.07@...il.com>
> Reported-by: Jonathan Corbet <corbet@....net>

Acked-by: Casey Schaufler <casey@...aufler-ca.com>

> --
> 
>  security/smack/smackfs.c |   35 ++---------------------------------
>  1 file changed, 2 insertions(+), 33 deletions(-)
> 
> diff --git a/security/smack/smackfs.c b/security/smack/smackfs.c
> index afe7c9b..cfae8af 100644
> --- a/security/smack/smackfs.c
> +++ b/security/smack/smackfs.c
> @@ -74,11 +74,6 @@ struct smk_list_entry *smack_list;
>  #define	SEQ_READ_FINISHED	1
>  
>  /*
> - * Disable concurrent writing open() operations
> - */
> -static struct semaphore smack_write_sem;
> -
> -/*
>   * Values for parsing cipso rules
>   * SMK_DIGITLEN: Length of a digit field in a rule.
>   * SMK_CIPSOMIN: Minimum possible cipso rule length.
> @@ -168,32 +163,7 @@ static struct seq_operations load_seq_ops = {
>   */
>  static int smk_open_load(struct inode *inode, struct file *file)
>  {
> -	if ((file->f_flags & O_ACCMODE) == O_RDONLY)
> -		return seq_open(file, &load_seq_ops);
> -
> -	if (down_interruptible(&smack_write_sem))
> -		return -ERESTARTSYS;
> -
> -	return 0;
> -}
> -
> -/**
> - * smk_release_load - release() for /smack/load
> - * @inode: inode structure representing file
> - * @file: "load" file pointer
> - *
> - * For a reading session, use the seq_file release
> - * implementation.
> - * Otherwise, we are at the end of a writing session so
> - * clean everything up.
> - */
> -static int smk_release_load(struct inode *inode, struct file *file)
> -{
> -	if ((file->f_flags & O_ACCMODE) == O_RDONLY)
> -		return seq_release(inode, file);
> -
> -	up(&smack_write_sem);
> -	return 0;
> +	return seq_open(file, &load_seq_ops);
>  }
>  
>  /**
> @@ -341,7 +311,7 @@ static const struct file_operations smk_load_ops = {
>  	.read		= seq_read,
>  	.llseek         = seq_lseek,
>  	.write		= smk_write_load,
> -	.release        = smk_release_load,
> +	.release        = seq_release,
>  };
>  
>  /**
> @@ -1011,7 +981,6 @@ static int __init init_smk_fs(void)
>  		}
>  	}
>  
> -	sema_init(&smack_write_sem, 1);
>  	smk_cipso_doi();
>  	smk_unlbl_ambient(NULL);
>  
> Regards,
> 
> -- 
> 
> "Better to light a candle, than curse the darkness"
> 
> Ahmed S. Darwish
> Homepage: http://darwish.07.googlepages.com
> Blog: http://darwish-07.blogspot.com
> 
> 
> 


Casey Schaufler
casey@...aufler-ca.com
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