Avoid overlapping addresses to stpcpy calls in nscd (BZ #16760)

Calls to stpcpy from nscd netgroups code will have overlapping source
and destination when all three values in the returned triplet are
non-NULL and in the expected (host,user,domain) order.  This is seen
in valgrind as:

==3181== Source and destination overlap in stpcpy(0x19973b48, 0x19973b48)
==3181==    at 0x4C2F30A: stpcpy (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==3181==    by 0x12567A: addgetnetgrentX (string3.h:111)
==3181==    by 0x12722D: addgetnetgrent (netgroupcache.c:665)
==3181==    by 0x11114C: nscd_run_worker (connections.c:1338)
==3181==    by 0x4E3C102: start_thread (pthread_create.c:309)
==3181==    by 0x59B81AC: clone (clone.S:111)
==3181==

Fix this by using memmove instead of stpcpy.

1 files changed, 10 insertions, 6 deletions

diff --git a/nscd/netgroupcache.c b/nscd/netgroupcache.c
index 5d15aa49f4..820d8234b4 100644
--- a/nscd/netgroupcache.c
+++ b/nscd/netgroupcache.c
@@ -216,6 +216,10 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
 			    const char *nuser = data.val.triple.user;
 			    const char *ndomain = data.val.triple.domain;
 
+			    size_t hostlen = strlen (nhost ?: "") + 1;
+			    size_t userlen = strlen (nuser ?: "") + 1;
+			    size_t domainlen = strlen (ndomain ?: "") + 1;
+
 			    if (nhost == NULL || nuser == NULL || ndomain == NULL
 				|| nhost > nuser || nuser > ndomain)
 			      {
@@ -233,9 +237,6 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
 				     : last + strlen (last) + 1 - buffer);
 
 				/* We have to make temporary copies.  */
-				size_t hostlen = strlen (nhost ?: "") + 1;
-				size_t userlen = strlen (nuser ?: "") + 1;
-				size_t domainlen = strlen (ndomain ?: "") + 1;
 				size_t needed = hostlen + userlen + domainlen;
 
 				if (buflen - req->key_len - bufused < needed)
@@ -269,9 +270,12 @@ addgetnetgrentX (struct database_dyn *db, int fd, request_header *req,
 			      }
 
 			    char *wp = buffer + buffilled;
-			    wp = stpcpy (wp, nhost) + 1;
-			    wp = stpcpy (wp, nuser) + 1;
-			    wp = stpcpy (wp, ndomain) + 1;
+			    wp = memmove (wp, nhost ?: "", hostlen);
+			    wp += hostlen;
+			    wp = memmove (wp, nuser ?: "", userlen);
+			    wp += userlen;
+			    wp = memmove (wp, ndomain ?: "", domainlen);
+			    wp += domainlen;
 			    buffilled = wp - buffer;
 			    ++nentries;
 			  }