[PATCH 07/13] sysfs: add ->seq_show support to sysfs_ops

Christoph Hellwig
2021-09-13T05:49:31Z

Allow attributes to directly use the seq_file method instead of
carving out a buffer that can easily lead to buffer overflows.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/sysfs/file.c | 19 ++++++++++++++-----
include/linux/sysfs.h | 9 +++++++--
2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 42dcf96881b68..12e0bfe40a2b4 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -45,6 +45,9 @@ static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
ssize_t count;
char *buf;

+ if (ops->seq_show)
+ return ops->seq_show(kobj, of->kn->priv, sf);
+
if (WARN_ON_ONCE(!ops->show))
return -EINVAL;

@@ -268,6 +271,10 @@ int sysfs_add_file_mode_ns(struct kernfs_node *parent,
return -EINVAL;

if (mode & SYSFS_PREALLOC) {
+ if (WARN(sysfs_ops->seq_show, KERN_ERR
+ "seq_show not supported on prealloc file: %s\n",
+ kobject_name(kobj)))
+ return -EINVAL;
if (sysfs_ops->show && sysfs_ops->store)
ops = &sysfs_prealloc_kfops_rw;
else if (sysfs_ops->show)
@@ -275,12 +282,14 @@ int sysfs_add_file_mode_ns(struct kernfs_node *parent,
else if (sysfs_ops->store)
ops = &sysfs_prealloc_kfops_wo;
} else {
- if (sysfs_ops->show && sysfs_ops->store)
- ops = &sysfs_file_kfops_rw;
- else if (sysfs_ops->show)
- ops = &sysfs_file_kfops_ro;
- else if (sysfs_ops->store)
+ if (sysfs_ops->seq_show || sysfs_ops->show) {
+ if (sysfs_ops->store)
+ ops = &sysfs_file_kfops_rw;
+ else
+ ops = &sysfs_file_kfops_ro;
+ } else if (sysfs_ops->store) {
ops = &sysfs_file_kfops_wo;
+ }
}

if (!ops)
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index e3f1e8ac1f85b..e1ab4da716730 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -236,8 +236,13 @@ struct bin_attribute bin_attr_##_name = __BIN_ATTR_WO(_name, _size)
struct bin_attribute bin_attr_##_name = __BIN_ATTR_RW(_name, _size)

struct sysfs_ops {
- ssize_t (*show)(struct kobject *, struct attribute *, char *);
- ssize_t (*store)(struct kobject *, struct attribute *, const char *, size_t);
+ int (*seq_show)(struct kobject *kobj, struct attribute *attr,
+ struct seq_file *sf);
+ ssize_t (*store)(struct kobject *kobj, struct attribute *attr,
+ const char *buf, size_t size);
+
+ /* deprecated except for preallocated attributes: */
+ ssize_t (*show)(struct kobject *kob, struct attribute *attr, char *buf);
};

#ifdef CONFIG_SYSFS
--
2.30.2