Re: [for-next][PATCH] tracefs: Fix refcount imbalance in start_creating()

[Steven Rostedt]

Forgot to Cc Daniel.

-- Steve


On Thu, 5 Nov 2015 08:29:33 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

>   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
> for-next
> 
> Head SHA1: d227c3ae4e94e5eb11dd780a811f59e1a7b74ccd
> 
> 
> Daniel Borkmann (1):
>       tracefs: Fix refcount imbalance in start_creating()
> 
> ----
>  fs/tracefs/inode.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> ---------------------------
> commit d227c3ae4e94e5eb11dd780a811f59e1a7b74ccd
> Author: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Date:   Wed Nov 4 23:33:17 2015 +0100
> 
>     tracefs: Fix refcount imbalance in start_creating()
>     
>     In tracefs' start_creating(), we pin the file system to safely access
>     its root. When we failed to create a file, we unpin the file system via
>     failed_creating() to release the mount count and eventually the reference
>     of the singleton vfsmount.
>     
>     However, when we run into an error during lookup_one_len() when still
>     in start_creating(), we only release the parent's mutex but not so the
>     reference on the mount.
>     
>     F.e., in securityfs_create_file(), after doing simple_pin_fs() when
>     lookup_one_len() fails there, we infact do simple_release_fs(). This
>     seems necessary here as well.
>     
>     Same issue seen in debugfs due to 190afd81e4a5 ("debugfs: split the
>     beginning and the end of __create_file() off"), which seemed to got
>     carried over into tracefs, too. Noticed during code review.
>     
>     Link: http://lkml.kernel.org/r/68efa86101b778cf7517ed7c6ad573bd69f60ec6.1446672850.git.daniel@xxxxxxxxxxxxx
>     
>     Fixes: 4282d60689d4 ("tracefs: Add new tracefs file system")
>     Cc: stable@xxxxxxxxxxxxxxx # 4.1+
>     Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
>     Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> 
> diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
> index cbc8d5d2755a..c66f2423e1f5 100644
> --- a/fs/tracefs/inode.c
> +++ b/fs/tracefs/inode.c
> @@ -340,8 +340,12 @@ static struct dentry *start_creating(const char *name, struct dentry *parent)
>  		dput(dentry);
>  		dentry = ERR_PTR(-EEXIST);
>  	}
> -	if (IS_ERR(dentry))
> +
> +	if (IS_ERR(dentry)) {
>  		mutex_unlock(&parent->d_inode->i_mutex);
> +		simple_release_fs(&tracefs_mount, &tracefs_mount_count);
> +	}
> +
>  	return dentry;
>  }
>  

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