[PATCH 46/75] sysfs: Introduce sysfs_rename_mutex

Greg Kroah-Hartman
2007-10-12T22:45:58Z

From: Eric W. Biederman <ebiederm@xmission.com>

Looking carefully at the rename code we have a subtle dependency
that the structure of sysfs not change while we are performing
a rename. If the parent directory of the object we are renaming
changes while the rename is being performed nasty things could
happen when we go to release our locks.

So introduce a sysfs_rename_mutex to prevent this highly
unlikely theoretical issue.

In addition hold sysfs_rename_mutex over all calls to
sysfs_get_dentry. Allowing sysfs_get_dentry to be simplified
in the future.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/sysfs/dir.c | 8 +++++++-
fs/sysfs/file.c | 4 ++++
fs/sysfs/sysfs.h | 1 +
3 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 1af963e..9fe83d2 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -15,6 +15,7 @@
#include "sysfs.h"

DEFINE_MUTEX(sysfs_mutex);
+DEFINE_MUTEX(sysfs_rename_mutex);
spinlock_t sysfs_assoc_lock = SPIN_LOCK_UNLOCKED;

static spinlock_t sysfs_ino_lock = SPIN_LOCK_UNLOCKED;
@@ -82,7 +83,7 @@ static void sysfs_unlink_sibling(struct sysfs_dirent *sd)
* down from there looking up dentry for each step.
*
* LOCKING:
- * Kernel thread context (may sleep)
+ * mutex_lock(sysfs_rename_mutex)
*
* RETURNS:
* Pointer to found dentry on success, ERR_PTR() value on error.
@@ -858,6 +859,8 @@ int sysfs_rename_dir(struct kobject * kobj, const char *new_name)
const char *dup_name = NULL;
int error;

+ mutex_lock(&sysfs_rename_mutex);
+
/* get the original dentry */
sd = kobj->sd;
old_dentry = sysfs_get_dentry(sd);
@@ -915,6 +918,7 @@ int sysfs_rename_dir(struct kobject * kobj, const char *new_name)
kfree(dup_name);
dput(old_dentry);
dput(new_dentry);
+ mutex_unlock(&sysfs_rename_mutex);
return error;
}

@@ -926,6 +930,7 @@ int sysfs_move_dir(struct kobject *kobj, struct kobject *new_parent_kobj)
struct dentry *old_dentry = NULL, *new_dentry = NULL;
int error;

+ mutex_lock(&sysfs_rename_mutex);
BUG_ON(!sd->s_parent);
new_parent_sd = new_parent_kobj->sd ? new_parent_kobj->sd : &sysfs_root;

@@ -982,6 +987,7 @@ again:
dput(new_parent);
dput(old_dentry);
dput(new_dentry);
+ mutex_unlock(&sysfs_rename_mutex);
return error;
}

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 16f39c3..ff93c92 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -470,7 +470,9 @@ int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
if (!victim_sd)
goto out;

+ mutex_lock(&sysfs_rename_mutex);
victim = sysfs_get_dentry(victim_sd);
+ mutex_unlock(&sysfs_rename_mutex);
if (IS_ERR(victim)) {
rc = PTR_ERR(victim);
victim = NULL;
@@ -509,7 +511,9 @@ int sysfs_chmod_file(struct kobject *kobj, struct attribute *attr, mode_t mode)
if (!victim_sd)
goto out;

+ mutex_lock(&sysfs_rename_mutex);
victim = sysfs_get_dentry(victim_sd);
+ mutex_unlock(&sysfs_rename_mutex);
if (IS_ERR(victim)) {
rc = PTR_ERR(victim);
victim = NULL;
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 77253aa..179e6a2 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -90,6 +90,7 @@ extern int sysfs_setattr(struct dentry *dentry, struct iattr *iattr);

extern spinlock_t sysfs_assoc_lock;
extern struct mutex sysfs_mutex;
+extern struct mutex sysfs_rename_mutex;
extern struct super_block * sysfs_sb;
extern const struct file_operations sysfs_dir_operations;
extern const struct file_operations sysfs_file_operations;
--
1.5.3.4