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Subject[PATCH] sysfs: Add sysfs_emit to replace sprintf to PAGE_SIZE buffers.
Date
sprintf does not know the PAGE_SIZE maximum of the temporary buffer
used for outputting sysfs content requests and it's possible to
overrun the buffer length.

Add a generic sysfs_emit mechanism that knows that the size of the
temporary buffer and ensures that no overrun is done.

Signed-off-by: Joe Perches <joe@perches.com>
---
fs/sysfs/file.c | 30 ++++++++++++++++++++++++++++++
include/linux/sysfs.h | 8 ++++++++
2 files changed, 38 insertions(+)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index eb6897ab78e7..06a13bbd7080 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -707,3 +707,33 @@ int sysfs_change_owner(struct kobject *kobj, kuid_t kuid, kgid_t kgid)
return 0;
}
EXPORT_SYMBOL_GPL(sysfs_change_owner);
+
+/**
+ * sysfs_emit - scnprintf equivalent, aware of PAGE_SIZE buffer.
+ * @buf: start of PAGE_SIZE buffer.
+ * @pos: current position in buffer
+ * (pos - buf) must always be < PAGE_SIZE
+ * @fmt: format
+ * @...: arguments to format
+ *
+ *
+ * Returns number of characters written at pos.
+ */
+int sysfs_emit(char *buf, char *pos, const char *fmt, ...)
+{
+ va_list args;
+ bool bad_pos = pos < buf;
+ bool bad_len = (pos - buf) >= PAGE_SIZE;
+ int len;
+
+ if (WARN(bad_pos || bad_len, "(pos < buf):%d (pos >= PAGE_SIZE):%d\n",
+ bad_pos, bad_len))
+ return 0;
+
+ va_start(args, fmt);
+ len = vscnprintf(pos, PAGE_SIZE - (pos - buf), fmt, args);
+ va_end(args);
+
+ return len;
+}
+EXPORT_SYMBOL_GPL(sysfs_emit);
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 34e84122f635..5a21d3d30016 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -329,6 +329,8 @@ int sysfs_groups_change_owner(struct kobject *kobj,
int sysfs_group_change_owner(struct kobject *kobj,
const struct attribute_group *groups, kuid_t kuid,
kgid_t kgid);
+__printf(3, 4)
+int sysfs_emit(char *buf, char *pos, const char *fmt, ...);

#else /* CONFIG_SYSFS */

@@ -576,6 +578,12 @@ static inline int sysfs_group_change_owner(struct kobject *kobj,
return 0;
}

+__printf(3, 4)
+static inline int sysfs_emit(char *buf, char *pos, const char *fmt, ...)
+{
+ return 0;
+}
+
#endif /* CONFIG_SYSFS */

static inline int __must_check sysfs_create_file(struct kobject *kobj,
--
2.26.0
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