On Thu, Nov 08, 2007 at 06:53:40PM +0800, Miao Xie wrote:
>Hi,every one.
> 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 <[EMAIL PROTECTED]>
>
>---
> kernel/time/clocksource.c | 19 ++++++++++---------
> 1 files changed, 10 insertions(+), 9 deletions(-)
>
>diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
>index c8a9d13..5d5926f 100644
>--- a/kernel/time/clocksource.c
>+++ b/kernel/time/clocksource.c
>@@ -342,15 +342,13 @@ void clocksource_change_rating(struct clocksource
>*cs, int rating)
> 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);
Yes, snprintf is safer than sprintf. But here, the 'count' will be
mis-pointed when snprintf returns no less than PAGE_SIZE (what you called
overflow). So you may also need:
if (unlikely(count >= PAGE_SIZE))
count = PAGE_SIZE - 1;
Just a simple guess. ;)
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