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authorJoe Perches <joe@perches.com>2020-09-16 13:40:38 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-10-02 12:02:30 +0200
commit2efc459d06f1630001e3984854848a5647086232 (patch)
tree5489a527a724c8a17bf96df38744504f0acb74b3
parente5e5fcef600e94d83c6542cdcca3ab6dada95946 (diff)
sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output
Output defects can exist in sysfs content using sprintf and snprintf. sprintf does not know the PAGE_SIZE maximum of the temporary buffer used for outputting sysfs content and it's possible to overrun the PAGE_SIZE buffer length. Add a generic sysfs_emit function that knows that the size of the temporary buffer and ensures that no overrun is done. Add a generic sysfs_emit_at function that can be used in multiple call situations that also ensures that no overrun is done. Validate the output buffer argument to be page aligned. Validate the offset len argument to be within the PAGE_SIZE buf. Signed-off-by: Joe Perches <joe@perches.com> Link: https://lore.kernel.org/r/884235202216d464d61ee975f7465332c86f76b2.1600285923.git.joe@perches.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--Documentation/filesystems/sysfs.rst8
-rw-r--r--fs/sysfs/file.c55
-rw-r--r--include/linux/sysfs.h15
3 files changed, 73 insertions, 5 deletions
diff --git a/Documentation/filesystems/sysfs.rst b/Documentation/filesystems/sysfs.rst
index ab0f7795792b..d44249050f4a 100644
--- a/Documentation/filesystems/sysfs.rst
+++ b/Documentation/filesystems/sysfs.rst
@@ -242,12 +242,10 @@ Other notes:
is 4096.
- show() methods should return the number of bytes printed into the
- buffer. This is the return value of scnprintf().
+ buffer.
-- show() must not use snprintf() when formatting the value to be
- returned to user space. If you can guarantee that an overflow
- will never happen you can use sprintf() otherwise you must use
- scnprintf().
+- show() should only use sysfs_emit() or sysfs_emit_at() when formatting
+ the value to be returned to user space.
- store() should return the number of bytes used from the buffer. If the
entire buffer has been used, just return the count argument.
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index eb6897ab78e7..96d0da65e088 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -15,6 +15,7 @@
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/seq_file.h>
+#include <linux/mm.h>
#include "sysfs.h"
@@ -707,3 +708,57 @@ 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.
+ * @fmt: format
+ * @...: optional arguments to @format
+ *
+ *
+ * Returns number of characters written to @buf.
+ */
+int sysfs_emit(char *buf, const char *fmt, ...)
+{
+ va_list args;
+ int len;
+
+ if (WARN(!buf || offset_in_page(buf),
+ "invalid sysfs_emit: buf:%p\n", buf))
+ return 0;
+
+ va_start(args, fmt);
+ len = vscnprintf(buf, PAGE_SIZE, fmt, args);
+ va_end(args);
+
+ return len;
+}
+EXPORT_SYMBOL_GPL(sysfs_emit);
+
+/**
+ * sysfs_emit_at - scnprintf equivalent, aware of PAGE_SIZE buffer.
+ * @buf: start of PAGE_SIZE buffer.
+ * @at: offset in @buf to start write in bytes
+ * @at must be >= 0 && < PAGE_SIZE
+ * @fmt: format
+ * @...: optional arguments to @fmt
+ *
+ *
+ * Returns number of characters written starting at &@buf[@at].
+ */
+int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
+{
+ va_list args;
+ int len;
+
+ if (WARN(!buf || offset_in_page(buf) || at < 0 || at >= PAGE_SIZE,
+ "invalid sysfs_emit_at: buf:%p at:%d\n", buf, at))
+ return 0;
+
+ va_start(args, fmt);
+ len = vscnprintf(buf + at, PAGE_SIZE - at, fmt, args);
+ va_end(args);
+
+ return len;
+}
+EXPORT_SYMBOL_GPL(sysfs_emit_at);
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index 34e84122f635..2caa34c1ca1a 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -329,6 +329,10 @@ 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(2, 3)
+int sysfs_emit(char *buf, const char *fmt, ...);
+__printf(3, 4)
+int sysfs_emit_at(char *buf, int at, const char *fmt, ...);
#else /* CONFIG_SYSFS */
@@ -576,6 +580,17 @@ static inline int sysfs_group_change_owner(struct kobject *kobj,
return 0;
}
+__printf(2, 3)
+static inline int sysfs_emit(char *buf, const char *fmt, ...)
+{
+ return 0;
+}
+
+__printf(3, 4)
+static inline int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
+{
+ return 0;
+}
#endif /* CONFIG_SYSFS */
static inline int __must_check sysfs_create_file(struct kobject *kobj,