Commit 5e2cb101 authored Feb 06, 2008 by Miao Xie Committed by Linus Torvalds Feb 06, 2008

time: fix sysfs_show_{available,current}_clocksources() buffer overflow problem



I found that there is a buffer overflow problem in the following code.

Version:	2.6.24-rc2,
File:		kernel/time/clocksource.c:417-432
--------------------------------------------------------------------
static ssize_t
sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
{
	struct clocksource *src;
	char *curr = buf;

	spin_lock_irq(&clocksource_lock);
	list_for_each_entry(src, &clocksource_list, list) {
		curr += sprintf(curr, "%s ", src->name);
	}
	spin_unlock_irq(&clocksource_lock);

	curr += sprintf(curr, "\n");

	return curr - buf;
}
-----------------------------------------------------------------------

sysfs_show_current_clocksources() also has the same problem though in practice
the size of current clocksource's name won't exceed PAGE_SIZE.

I fix the bug by using snprintf according to the specification of the kernel
(Version:2.6.24-rc2,File:Documentation/filesystems/sysfs.txt)

Fix sysfs_show_available_clocksources() and sysfs_show_current_clocksources()
buffer overflow problem with snprintf().

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent be6c28e6

kernel/time/clocksource.c

+10 −9

Original line number	Diff line number	Diff line
		@@ -363,15 +363,13 @@ void clocksource_unregister(struct clocksource *cs)
		static ssize_t
		sysfs_show_current_clocksources(struct sys_device dev, char buf)
		{
		char *curr = buf;
		ssize_t count = 0;

		spin_lock_irq(&clocksource_lock);
		curr += sprintf(curr, "%s ", curr_clocksource->name);
		count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
		spin_unlock_irq(&clocksource_lock);

		curr += sprintf(curr, "\n");

		return curr - buf;
		return count;
		}

		/**
		@@ -439,17 +437,20 @@ static ssize_t
		sysfs_show_available_clocksources(struct sys_device dev, char buf)
		{
		struct clocksource *src;
		char *curr = buf;
		ssize_t count = 0;

		spin_lock_irq(&clocksource_lock);
		list_for_each_entry(src, &clocksource_list, list) {
		curr += sprintf(curr, "%s ", src->name);
		count += snprintf(buf + count,
		max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
		"%s ", src->name);
		}
		spin_unlock_irq(&clocksource_lock);

		curr += sprintf(curr, "\n");
		count += snprintf(buf + count,
		max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");

		return curr - buf;
		return count;
		}

		/*

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