NetBSD Problem Report #56531
From www@netbsd.org Wed Dec 1 21:29:42 2021
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for <gnats-bugs@gnats.NetBSD.org>; Wed, 1 Dec 2021 21:29:42 +0000 (UTC)
Message-Id: <20211201212941.6346D1A9239@mollari.NetBSD.org>
Date: Wed, 1 Dec 2021 21:29:41 +0000 (UTC)
From: anthony.mallet@laas.fr
Reply-To: anthony.mallet@laas.fr
To: gnats-bugs@NetBSD.org
Subject: Huge buffer stack in getaddrinfo(3)
X-Send-Pr-Version: www-1.0
>Number: 56531
>Category: lib
>Synopsis: Huge buffer stack in getaddrinfo(3)
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: lib-bug-people
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Wed Dec 01 21:30:00 +0000 2021
>Originator: Anthony Mallet
>Release: -current
>Organization:
>Environment:
NetBSD ficus 9.99.91 NetBSD 9.99.91 (FICUS) #31: Sat Oct 16 15:04:36 CEST 2021 troot@ficus:/usr/obj/sys/arch/amd64/compile/FICUS amd64
>Description:
There is a 64kB buffer allocated on the stack in the res_queryN function used by getaddrinfo(3).
https://anonhg.netbsd.org/src/file/tip/lib/libc/net/getaddrinfo.c#l2550
While this is in general not an issue, it can become troublesome in a multi-threaded context with a small custom stack size. While the stack size can be increased, it is a bit unusual to allocate such a big buffer on the stack.
This was discussed in tech-userlevel
http://mail-index.netbsd.org/tech-userlevel/2021/11/28/msg013174.html
In rev. 1.63:
http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/net/getaddrinfo.c.diff?r1=1.62&r2=1.63
I believe that the intent of the commit was to increase the buffer size used to read DNS replies. As a (probably unwanted) side effect, this modified the buffer size used only to send queries.
This may be confirmed by the fact that a very similar function res_nquery()
https://anonhg.netbsd.org/src/file/tip/lib/libc/resolv/res_query.c#l145
does the same thing with a smaller buffer.
So I think it should be shrink the buffer used in res_queryN to the size it was before rev. 1.63 of getaddrinfo.c, as suggested in the attached patch.
If it is believed that the buffer should remain at 64kB, I also can provide a patch that allocates the buffer on the heap instead.
>How-To-Repeat:
>Fix:
Index: getaddrinfo.c
===================================================================
RCS file: /cvsroot/src/lib/libc/net/getaddrinfo.c,v
retrieving revision 1.122
diff -u -r1.122 getaddrinfo.c
--- getaddrinfo.c 28 Oct 2021 20:56:32 -0000 1.122
+++ getaddrinfo.c 29 Nov 2021 15:56:07 -0000
@@ -211,6 +211,11 @@
{ 0, 0 }
};
+#if PACKETSZ > 1024
+#define MAXQUERY PACKETSZ
+#else
+#define MAXQUERY 1024
+#endif
#define MAXPACKET (64*1024)
typedef union {
@@ -2547,7 +2552,7 @@
res_queryN(const char *name, /* domain name */ struct res_target *target,
res_state statp)
{
- u_char buf[MAXPACKET];
+ u_char buf[MAXQUERY];
HEADER *hp;
int n;
struct res_target *t;
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$NetBSD: query-full-pr,v 1.46 2020/01/03 16:35:01 leot Exp $
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