[PATCH BUGFIX -rc6] Smackfs: remove redundant lock, fix open(,O_RDWR)

[PATCH BUGFIX -rc6] Smackfs: remove redundant lock, fix open(,O_RDWR)

[Ahmed S. Darwish]

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@gmail.com>
Reported-by: Jonathan Corbet <corbet@lwn.net>
--

 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

Re: [PATCH BUGFIX -rc6] Smackfs: remove redundant lock, fix open(,O_RDWR)

[Casey Schaufler]

--- "Ahmed S. Darwish" <darwish.07@gmail.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@gmail.com>
> Reported-by: Jonathan Corbet <corbet@lwn.net>

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