Date: Sat, 21 Aug 2004 10:19:25 -0700 From: Tim Kientzle <kientzle@freebsd.org> To: Sean McNeil <sean@mcneil.com> Cc: freebsd-current@freebsd.org Subject: Re: bsdtar core dumps Message-ID: <4127841D.6050104@freebsd.org> In-Reply-To: <1092951447.1167.12.camel@server.mcneil.com> References: <1092777586.92327.9.camel@server.mcneil.com> <20040817213813.GE3827@gothmog.gr> <1092951447.1167.12.camel@server.mcneil.com>
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Sean McNeil wrote:
>>>
>>>I just tried to unarchive a file that didn't exist and got a core dump:
>
> Here is a backtrace of the error:
>
> #0 0x0000000200926d7e in __vfprintf (fp=0x7fffffffe360,
> fmt0=0x4161d9 "Failed to open '%s'", ap=0x7fffffffe640)
> at /usr/src/lib/libc/stdio/vfprintf.c:1052
> #1 0x00000002008c4006 in vsnprintf (str=0x32 <Address 0x32 out of bounds>,
> n=4284889, fmt=0x4161d9 "Failed to open '%s'", ap=0x7fffffffe640)
> at /usr/src/lib/libc/stdio/vsnprintf.c:75
> #2 0x0000000000411478 in __archive_string_vsprintf (as=0x520240,
> fmt=0x4161d9 "Failed to open '%s'", ap=0x7fffffffe640)
> at /usr/src/lib/libarchive/archive_string_sprintf.c:60
>
> Could be a compiler bug I suppose, but more likely I think it is this
> code:
>
> if (n == 0) {
> if (on > 0)
> *str = '\0';
> str = dummy;
> n = 1;
> }
>
> in vsnprintf.c::vsnprintf.
The code you've pointed to above concerns
me because of the part about:
if (n == 0) {
...
n = 1;
}
That ain't right: If I told vsnprintf the buffer
size was zero, it should treat it as such. If I
meant "one", I would have said "one."
On the other hand, the vsnprintf.3 man page
does explicitly state that "the output is always
null-terminated," which would preclude passing
a zero-length buffer, which is exactly what
libarchive is doing in this situation. It is
bogus, but at least it's documented bogosity. ;-)
Please try the attached patch to libarchive/archive_string_sprintf.c
and let me know if it works for you. It simply
forces the target buffer to be allocated and thereby
avoids calling vsnprintf with a NULL buffer.
Tim Kientzle
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Index: archive_string_sprintf.c
===================================================================
RCS file: /home/ncvs/src/lib/libarchive/archive_string_sprintf.c,v
retrieving revision 1.4
diff -u -r1.4 archive_string_sprintf.c
--- archive_string_sprintf.c 14 Aug 2004 03:45:45 -0000 1.4
+++ archive_string_sprintf.c 21 Aug 2004 17:02:49 -0000
@@ -48,6 +48,9 @@
{
size_t l;
+ /* Make sure the target area is initialized. */
+ __archive_string_ensure(as, 64);
+
if (fmt == NULL) {
as->s[0] = 0;
return;
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