sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output

commit 2efc459d06f1630001e3984854848a5647086232 upstream.

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>

diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt
index a1426cabcef12c814ed3527e0d8663eddea8277b..2e38fafc1b6329ceef4dcf47b88b54e923c1a93d 100644 (file)
--- a/Documentation/filesystems/sysfs.txt
+++ b/Documentation/filesystems/sysfs.txt
@@ -211,12 +211,10 @@ 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 0a7252aecfa534fea4bcb9a570dc4db2b134b44f..5166eb40917dac2e1bcc54f11c5d14ea927b3bde 100644 (file)
--- 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"
 #include "../kernfs/kernfs-internal.h"
@@ -556,3 +557,57 @@ void sysfs_remove_bin_file(struct kobject *kobj,
        kernfs_remove_by_name(kobj->sd, attr->attr.name);
 }
 EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);
+
+/**
+ *     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 987cefa337de672c44cecedc281eed3b32aff11d..1cd7bad56075ba975515b3c695fdb8a1de216abb 100644 (file)
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -299,6 +299,11 @@ static inline void sysfs_enable_ns(struct kernfs_node *kn)
        return kernfs_enable_ns(kn);
 }
 
+__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 */
 
 static inline int sysfs_create_dir_ns(struct kobject *kobj, const void *ns)
@@ -505,6 +510,17 @@ static inline void sysfs_enable_ns(struct kernfs_node *kn)
 {
 }
 
+__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,