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Subject[PATCH 03/15] sysfs: Use dentry_ops instead of directly playing with the dcache
Date
From: Eric W. Biederman <ebiederm@xmission.com>

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>
---
fs/sysfs/dir.c | 73 +++++++++++++++++++++++++++++++++++--------------------
1 files changed, 46 insertions(+), 27 deletions(-)
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 130dfc3..b5e8499 100644
--- 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);
--
1.6.5.2.143.g8cc62


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