[PATCH] Fix incorrect getaddrinfo assertion trigger

[Allan McRae <allan at archlinux dot org>]

[BS #9954]

With the following /etc/hosts:
127.0.0.1       www.my-domain.es
127.0.1.1       www.my-domain.es
192.168.0.1     www.my-domain.es

Using getaddrinfo() on www.my-domain.es, trigger the following assertion:
../sysdeps/posix/getaddrinfo.c:1473: rfc3484_sort: Assertion
`src->results[i].native == -1 || src->results[i].native == a1_native' failed.

This is due to two different bugs:
- In rfc3484_sort() rule 7, src->results[i].native is assigned even if
src->results[i].index is -1, meaning that no interface is associated.
- In getaddrinfo() the source IP address used with the lo interface needs a
special case, as it can be any IP within 127.X.Y.Z.

---

This is a patch taken from bugzilla.  I can not replicate it myself, even
with the attached testcase on bugzilla.  However, I have users reporting this
issue that also can confirm this patch fixes the assertions for them.  I
believe this patch is widely used by other distributions (at least Debian
and Fedora).

There is a negative comment by Ulrich here:
https://sourceware.org/bugzilla/show_bug.cgi?id=9954#c2

I think that comment is partially correct, in that it is hiding a bug from
a faulty DNS provider, in which case this patch is correct in that it
improves robustness.  That is why this bug does not affect most people.
However, I am not fully confident about that assessment...

Can anyone replicate or confirm/correct my reasoning why most people can
not replicate?



20xx-xx-xx  Aurelien Jarno  <aurelien@aurel32.net>

	[BS #9954]
	* sysdeps/posix/getaddrinfo.c (rfc3484_sort): do not assign native
	result if the result has no associated interface.
	* sysdeps/posix/getaddrinfo.c (getaddrinfo): correctly detect 
	interface for all 127.X.Y.Z addresses.


 sysdeps/posix/getaddrinfo.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/sysdeps/posix/getaddrinfo.c b/sysdeps/posix/getaddrinfo.c
index 52177e4..c0ded84 100644
--- a/sysdeps/posix/getaddrinfo.c
+++ b/sysdeps/posix/getaddrinfo.c
@@ -1735,13 +1735,13 @@ rfc3484_sort (const void *p1, const void *p2, void *arg)
 
 	      /* Fill in the results in all the records.  */
 	      for (int i = 0; i < src->nresults; ++i)
-		if (src->results[i].index == a1_index)
+		if (a1_index != -1 && src->results[i].index == a1_index)
 		  {
 		    assert (src->results[i].native == -1
 			    || src->results[i].native == a1_native);
 		    src->results[i].native = a1_native;
 		  }
-		else if (src->results[i].index == a2_index)
+		else if (a2_index != -1 && src->results[i].index == a2_index)
 		  {
 		    assert (src->results[i].native == -1
 			    || src->results[i].native == a2_native);
@@ -2601,7 +2601,14 @@ getaddrinfo (const char *name, const char *service,
 			  tmp.addr[0] = 0;
 			  tmp.addr[1] = 0;
 			  tmp.addr[2] = htonl (0xffff);
-			  tmp.addr[3] = sinp->sin_addr.s_addr;
+			  /* Special case for lo interface, the source address
+			     being possibly different than the interface 
+			     address. */
+			  if ((ntohl(sinp->sin_addr.s_addr) & 0xff000000)
+			      == 0x7f000000)
+			    tmp.addr[3] = htonl(0x7f000001);
+			  else
+			    tmp.addr[3] = sinp->sin_addr.s_addr;
 			}
 		      else
 			{
-- 
1.8.4