From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Mon, 4 Feb 2013 14:56:26 +0000 (+0100)
Subject: nss-myhostname: copy first result to preallocated buffer
X-Git-Tag: v198~336
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=commitdiff_plain;h=d2f1f23ad2636cf05589a67b5229c7fd604bc21f;hp=13219b7f74cb2722746b953bbec7593d5cc665e3

nss-myhostname: copy first result to preallocated buffer

Fixes a segfault in nscd when using nss-myhostname.

Nscd expects that an NSS module's gethostbyname4_r function returns
its first result in the pre-allocated gaih_addrtuple denoted by **pat.
(See nscd/aicache.c in the Glibc sources.)  However, nss-myhostname
doesn't fill in **pat but allocates the first result in ‘buffer’, then
sets *pat.  So nscd crashes (e.g. when running ‘getent ahosts
my-machine’).

Hard to tell if this is a bug in nscd, since there doesn't seem to be
a proper API spec for gethostbyname4_r.  But in any case, this patch
fixes the crash by copying the first result to **pat.
---

diff --git a/src/nss-myhostname/nss-myhostname.c b/src/nss-myhostname/nss-myhostname.c
index 834a80690..b0fb8323a 100644
--- a/src/nss-myhostname/nss-myhostname.c
+++ b/src/nss-myhostname/nss-myhostname.c
@@ -176,7 +176,11 @@ enum nss_status _nss_myhostname_gethostbyname4_r(
         /* Verify the size matches */
         assert(idx == ms);
 
-        *pat = r_tuple_prev;
+        /* Nscd expects us to store the first record in **pat. */
+        if (*pat)
+                **pat = *r_tuple_prev;
+        else
+                *pat = r_tuple_prev;
 
         if (ttlp)
                 *ttlp = 0;