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Date: Thu, 2 Nov 2006 08:26:27 +0000
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Subject: Reentrant problem with inet_ntoa in the kernel
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Hi,

I am confused by the use of inet_ntoa function in the kernel.

The function inet_ntoa in the /sys/libkern/inet_ntoa.c uses a static array
static char buf[4 * sizeof "123"];
to store the result. And it returns the address of the array to the caller.

I think this inet_ntoa is not reentrant, though there are several functions
calling it. If two functions call it simultaneously, the result will be
corrupted. Though I haven't really encountered this situation, it may occur
someday, especially when using multi-processors.

There is another reentrant version of inet_ntoa called inet_ntoa_r in the
same file. It has been there for several years, but just used by ipfw2 for
about four times in 7-CURRENT. In my patch, I replaced all the calls to
inet_ntoa with calls to inet_ntoa_r.

By the way, some of the original calls is written in this style:
strcpy(buf, inet_ntoa(ip))
The modified code is written in this style
inet_ntoa_r(ip, buf)
This change avoids a call to strcpy, and can save a little time.

Here is the patch.
http://people.freebsd.org/~delphij/misc/patch-itoa-by-nodummy-at-yeah-net

I've already sent to PR(kern/104738), but got no reply, maybe it should be
discussed here first?


Thanks
MQ