Reentrant problem with inet_ntoa in the kernel

[Brooks Davis]

On Fri, Nov 03, 2006 at 09:46:47AM +0000, MQ wrote:
> 2006/11/2, Brooks Davis <brooks at one-eyed-alien.net>:
> >
> >On Thu, Nov 02, 2006 at 08:26:27AM +0000, . wrote:
> >> 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?
> >
> >I've got to agree with other posters that the stack variable allocations
> >are ugly.  What about extending log and printf to understand ip4v
> >addresses?  That's 90% of the uses and the others appears to have
> >buffers already.
> >
> >-- Brooks
> >
> >
> >Ugly? Why? Don't you use local variables in your sources?

The particular definition used is excedingly ugly.  At a minimum there
needs to be a define or a constant "16" for the lenght rather than the
4*sizeof("123") nonsense.

-- Brooks
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 187 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-net/attachments/20061103/38638b11/attachment.pgp