Commit 8118a859 authored Nov 21, 2007 by Miao Xie Committed by Greg Kroah-Hartman Nov 28, 2007

sysfs: fix off-by-one error in fill_read_buffer()



I found that there is a off-by-one problem in the following code.

Version:	2.6.24-rc2
File:		fs/sysfs/file.c:118-122
Function:	fill_read_buffer
--------------------------------------------------------------------
	count = ops->show(kobj, attr_sd->s_attr.attr, buffer->page);

	sysfs_put_active_two(attr_sd);

	BUG_ON(count > (ssize_t)PAGE_SIZE);
--------------------------------------------------------------------

Because according to the specification of the sysfs and the implement of
the show methods, the show methods return the number of bytes which would
be generated for the given input, excluding the trailing null.So if the
return value of the show methods equals PAGE_SIZE - 1, the buffer is full
in fact.  And if the return value equals PAGE_SIZE, the resulting string
was already truncated,or buffer overflow occurred.

This patch fixes an off-by-one error in fill_read_buffer.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Tejun Heo <teheo@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

parent 71409a49

fs/sysfs/file.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -119,7 +119,11 @@ static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer

		sysfs_put_active_two(attr_sd);

		BUG_ON(count > (ssize_t)PAGE_SIZE);
		/*
		* The code works fine with PAGE_SIZE return but it's likely to
		* indicate truncated result or overflow in normal use cases.
		*/
		BUG_ON(count >= (ssize_t)PAGE_SIZE);
		if (count >= 0) {
		buffer->needs_read_fill = 0;
		buffer->count = count;

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