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-rw-r--r--fs/sysfs/dir.c18
-rw-r--r--fs/sysfs/symlink.c20
-rw-r--r--fs/sysfs/sysfs.h2
3 files changed, 30 insertions, 10 deletions
diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index de47ed3..08c6696 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -26,7 +26,7 @@
#include "sysfs.h"
DEFINE_MUTEX(sysfs_mutex);
-DEFINE_SPINLOCK(sysfs_assoc_lock);
+DEFINE_SPINLOCK(sysfs_symlink_target_lock);
#define to_sysfs_dirent(X) rb_entry((X), struct sysfs_dirent, s_rb)
@@ -902,9 +902,21 @@ void sysfs_remove_dir(struct kobject *kobj)
{
struct sysfs_dirent *sd = kobj->sd;
- spin_lock(&sysfs_assoc_lock);
+ /*
+ * In general, kboject owner is responsible for ensuring removal
+ * doesn't race with other operations and sysfs doesn't provide any
+ * protection; however, when @kobj is used as a symlink target, the
+ * symlinking entity usually doesn't own @kobj and thus has no
+ * control over removal. @kobj->sd may be removed anytime and
+ * symlink code may end up dereferencing an already freed sd.
+ *
+ * sysfs_symlink_target_lock synchronizes @kobj->sd disassociation
+ * against symlink operations so that symlink code can safely
+ * dereference @kobj->sd.
+ */
+ spin_lock(&sysfs_symlink_target_lock);
kobj->sd = NULL;
- spin_unlock(&sysfs_assoc_lock);
+ spin_unlock(&sysfs_symlink_target_lock);
if (sd) {
WARN_ON_ONCE(sysfs_type(sd) != SYSFS_DIR);
diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
index 22ea2f5..1a23681 100644
--- a/fs/sysfs/symlink.c
+++ b/fs/sysfs/symlink.c
@@ -32,13 +32,15 @@ static int sysfs_do_create_link_sd(struct sysfs_dirent *parent_sd,
BUG_ON(!name || !parent_sd);
- /* target->sd can go away beneath us but is protected with
- * sysfs_assoc_lock. Fetch target_sd from it.
+ /*
+ * We don't own @target and it may be removed at any time.
+ * Synchronize using sysfs_symlink_target_lock. See
+ * sysfs_remove_dir() for details.
*/
- spin_lock(&sysfs_assoc_lock);
+ spin_lock(&sysfs_symlink_target_lock);
if (target->sd)
target_sd = sysfs_get(target->sd);
- spin_unlock(&sysfs_assoc_lock);
+ spin_unlock(&sysfs_symlink_target_lock);
error = -ENOENT;
if (!target_sd)
@@ -140,10 +142,16 @@ void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
const char *name)
{
const void *ns = NULL;
- spin_lock(&sysfs_assoc_lock);
+
+ /*
+ * We don't own @target and it may be removed at any time.
+ * Synchronize using sysfs_symlink_target_lock. See
+ * sysfs_remove_dir() for details.
+ */
+ spin_lock(&sysfs_symlink_target_lock);
if (targ->sd)
ns = targ->sd->s_ns;
- spin_unlock(&sysfs_assoc_lock);
+ spin_unlock(&sysfs_symlink_target_lock);
sysfs_hash_and_remove(kobj->sd, name, ns);
}
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 05d063f..e3aea92 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -159,7 +159,7 @@ extern struct kmem_cache *sysfs_dir_cachep;
* dir.c
*/
extern struct mutex sysfs_mutex;
-extern spinlock_t sysfs_assoc_lock;
+extern spinlock_t sysfs_symlink_target_lock;
extern const struct dentry_operations sysfs_dentry_ops;
extern const struct file_operations sysfs_dir_operations;
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