[ 074/104] cgroup: fix broken file xattrs

Greg Kroah-Hartman
2013-05-06T23:23:35Z

From: Li Zefan <lizefan@huawei.com>

commit 712317ad97f41e738e1a19aa0a6392a78a84094e upstream.

We should store file xattrs in struct cfent instead of struct cftype,
because cftype is a type while cfent is object instance of cftype.

For example each cgroup has a tasks file, and each tasks file is
associated with a uniq cfent, but all those files share the same
struct cftype.

Alexey Kodanev reported a crash, which can be reproduced:

# mount -t cgroup -o xattr /sys/fs/cgroup
# mkdir /sys/fs/cgroup/test
# setfattr -n trusted.value -v test_value /sys/fs/cgroup/tasks
# rmdir /sys/fs/cgroup/test
# umount /sys/fs/cgroup
oops!

In this case, simple_xattrs_free() will free the same struct simple_xattrs
twice.

tj: Dropped unused local variable @cft from cgroup_diput().

Reported-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/cgroup.h | 3 ---
kernel/cgroup.c | 11 ++++++-----
2 files changed, 6 insertions(+), 8 deletions(-)

--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -303,9 +303,6 @@ struct cftype {
/* CFTYPE_* flags */
unsigned int flags;

- /* file xattrs */
- struct simple_xattrs xattrs;
-
int (*open)(struct inode *inode, struct file *file);
ssize_t (*read)(struct cgroup *cgrp, struct cftype *cft,
struct file *file,
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -162,6 +162,9 @@ struct cfent {
struct list_head node;
struct dentry *dentry;
struct cftype *type;
+
+ /* file xattrs */
+ struct simple_xattrs xattrs;
};

/*
@@ -908,13 +911,12 @@ static void cgroup_diput(struct dentry *
} else {
struct cfent *cfe = __d_cfe(dentry);
struct cgroup *cgrp = dentry->d_parent->d_fsdata;
- struct cftype *cft = cfe->type;

WARN_ONCE(!list_empty(&cfe->node) &&
cgrp != &cgrp->root->top_cgroup,
"cfe still linked for %s\n", cfe->type->name);
+ simple_xattrs_free(&cfe->xattrs);
kfree(cfe);
- simple_xattrs_free(&cft->xattrs);
}
iput(inode);
}
@@ -2553,7 +2555,7 @@ static struct simple_xattrs *__d_xattrs(
if (S_ISDIR(dentry->d_inode->i_mode))
return &__d_cgrp(dentry)->xattrs;
else
- return &__d_cft(dentry)->xattrs;
+ return &__d_cfe(dentry)->xattrs;
}

static inline int xattr_enabled(struct dentry *dentry)
@@ -2729,8 +2731,6 @@ static int cgroup_add_file(struct cgroup
umode_t mode;
char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };

- simple_xattrs_init(&cft->xattrs);
-
if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
strcpy(name, subsys->name);
strcat(name, ".");
@@ -2755,6 +2755,7 @@ static int cgroup_add_file(struct cgroup
cfe->type = (void *)cft;
cfe->dentry = dentry;
dentry->d_fsdata = cfe;
+ simple_xattrs_init(&cfe->xattrs);
list_add_tail(&cfe->node, &parent->files);
cfe = NULL;
}