sysfs: Use dentry_ops instead of directly playing with the dcache

Calling d_drop unconditionally when a sysfs_dirent is deleted has
the potential to leak mounts, so instead implement dentry delete
and revalidate operations that cause sysfs dentries to be removed
at the appropriate time.

Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 01a9a64..9ee130b 100644 (file)
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -298,6 +298,46 @@ void release_sysfs_dirent(struct sysfs_dirent * sd)
                goto repeat;
 }
 
+static int sysfs_dentry_delete(struct dentry *dentry)
+{
+       struct sysfs_dirent *sd = dentry->d_fsdata;
+       return !!(sd->s_flags & SYSFS_FLAG_REMOVED);
+}
+
+static int sysfs_dentry_revalidate(struct dentry *dentry, struct nameidata *nd)
+{
+       struct sysfs_dirent *sd = dentry->d_fsdata;
+       int is_dir;
+
+       mutex_lock(&sysfs_mutex);
+
+       /* The sysfs dirent has been deleted */
+       if (sd->s_flags & SYSFS_FLAG_REMOVED)
+               goto out_bad;
+
+       mutex_unlock(&sysfs_mutex);
+out_valid:
+       return 1;
+out_bad:
+       /* Remove the dentry from the dcache hashes.
+        * If this is a deleted dentry we use d_drop instead of d_delete
+        * so sysfs doesn't need to cope with negative dentries.
+        */
+       is_dir = (sysfs_type(sd) == SYSFS_DIR);
+       mutex_unlock(&sysfs_mutex);
+       if (is_dir) {
+               /* If we have submounts we must allow the vfs caches
+                * to lie about the state of the filesystem to prevent
+                * leaks and other nasty things.
+                */
+               if (have_submounts(dentry))
+                       goto out_valid;
+               shrink_dcache_parent(dentry);
+       }
+       d_drop(dentry);
+       return 0;
+}
+
 static void sysfs_dentry_iput(struct dentry *dentry, struct inode *inode)
 {
        struct sysfs_dirent * sd = dentry->d_fsdata;
@@ -307,6 +347,8 @@ static void sysfs_dentry_iput(struct dentry *dentry, struct inode *inode)
 }
 
 static const struct dentry_operations sysfs_dentry_ops = {
+       .d_revalidate   = sysfs_dentry_revalidate,
+       .d_delete       = sysfs_dentry_delete,
        .d_iput         = sysfs_dentry_iput,
 };
 
@@ -527,44 +569,21 @@ void sysfs_remove_one(struct sysfs_addrm_cxt *acxt, struct sysfs_dirent *sd)
 }
 
 /**
- *     sysfs_drop_dentry - drop dentry for the specified sysfs_dirent
+ *     sysfs_dec_nlink - Decrement link count for the specified sysfs_dirent
  *     @sd: target sysfs_dirent
  *
- *     Drop dentry for @sd.  @sd must have been unlinked from its
+ *     Decrement nlink for @sd.  @sd must have been unlinked from its
  *     parent on entry to this function such that it can't be looked
  *     up anymore.
  */
-static void sysfs_drop_dentry(struct sysfs_dirent *sd)
+static void sysfs_dec_nlink(struct sysfs_dirent *sd)
 {
        struct inode *inode;
-       struct dentry *dentry;
 
        inode = ilookup(sysfs_sb, sd->s_ino);
        if (!inode)
                return;
 
-       /* Drop any existing dentries associated with sd.
-        *
-        * For the dentry to be properly freed we need to grab a
-        * reference to the dentry under the dcache lock,  unhash it,
-        * and then put it.  The playing with the dentry count allows
-        * dput to immediately free the dentry  if it is not in use.
-        */
-repeat:
-       spin_lock(&dcache_lock);
-       list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
-               if (d_unhashed(dentry))
-                       continue;
-               dget_locked(dentry);
-               spin_lock(&dentry->d_lock);
-               __d_drop(dentry);
-               spin_unlock(&dentry->d_lock);
-               spin_unlock(&dcache_lock);
-               dput(dentry);
-               goto repeat;
-       }
-       spin_unlock(&dcache_lock);
-
        /* adjust nlink and update timestamp */
        mutex_lock(&inode->i_mutex);
 
@@ -611,7 +630,7 @@ void sysfs_addrm_finish(struct sysfs_addrm_cxt *acxt)
                acxt->removed = sd->s_sibling;
                sd->s_sibling = NULL;
 
-               sysfs_drop_dentry(sd);
+               sysfs_dec_nlink(sd);
                sysfs_deactivate(sd);
                unmap_bin_file(sd);
                sysfs_put(sd);