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

[Steven Rostedt]

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
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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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