Commit bb2b0051 authored Apr 04, 2013 by Ming Lei Committed by Greg Kroah-Hartman Apr 05, 2013

sysfs: check if one entry has been removed before freeing



It might be a kernel disaster if one sysfs entry is freed but
still referenced by sysfs tree.

Recently Dave and Sasha reported one use-after-free problem on
sysfs entry, and the problem has been troubleshooted with help
of debug message added in this patch.

Given sysfs_get_dirent/sysfs_put are exported APIs, even inside
sysfs they are called in many contexts(kobject/attribe add/delete,
inode init/drop, dentry lookup/release, readdir, ...), it is healthful
to check the removed flag before freeing one entry and dump message
if it is freeing without being removed first.

Cc: Dave Jones <davej@redhat.com>
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent bcfb87fb

fs/sysfs/dir.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -268,6 +268,10 @@ void release_sysfs_dirent(struct sysfs_dirent * sd)
		*/
		parent_sd = sd->s_parent;

		WARN(!(sd->s_flags & SYSFS_FLAG_REMOVED),
		"sysfs: free using entry: %s/%s\n",
		parent_sd ? parent_sd->s_name : "", sd->s_name);

		if (sysfs_type(sd) == SYSFS_KOBJ_LINK)
		sysfs_put(sd->s_symlink.target_sd);
		if (sysfs_type(sd) & SYSFS_COPY_NAME)
		@@ -386,7 +390,7 @@ struct sysfs_dirent sysfs_new_dirent(const char name, umode_t mode, int type)

		sd->s_name = name;
		sd->s_mode = mode;
		sd->s_flags = type;
		sd->s_flags = type \| SYSFS_FLAG_REMOVED;

		return sd;

		@@ -466,6 +470,9 @@ int __sysfs_add_one(struct sysfs_addrm_cxt acxt, struct sysfs_dirent sd)
		ps_iattrs->ia_ctime = ps_iattrs->ia_mtime = CURRENT_TIME;
		}

		/* Mark the entry added into directory tree */
		sd->s_flags &= ~SYSFS_FLAG_REMOVED;

		return 0;
		}