commit 16b293a7a6f65d8ff348a603d19e8fd4372fa3a9
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date: Wed Apr 30 11:48:43 2014 +0530
Do not fail if one of the two responses to AF_UNSPEC fails (BZ #14308)
[Fixes BZ #14308, #12994, #13651]
AF_UNSPEC results in sending two queries in parallel, one for the A
record and the other for the AAAA record. If one of these is a
referral, then the query fails, which is wrong. It should return at
least the one successful response.
The fix has two parts. The first part makes the referral fall back to
the SERVFAIL path, which results in using the successful response.
There is a bug in that path however, due to which the second part is
necessary. The bug here is that if the first response is a failure
and the second succeeds, __libc_res_nsearch does not detect that and
assumes a failure. The case where the first response is a success and
the second fails, works correctly.
This condition is produced by buggy routers, so here's a crude
interposable library that can simulate such a condition. The library
overrides the recvfrom syscall and modifies the header of the packet
received to reproduce this scenario. It has two key variables:
mod_packet and first_error.
The mod_packet variable when set to 0, results in odd packets being
modified to be a referral. When set to 1, even packets are modified
to be a referral.
The first_error causes the first response to be a failure so that a
domain-appended search is performed to test the second part of the
__libc_nsearch fix.
The driver for this fix is a simple getaddrinfo program that does an
AF_UNSPEC query. I have omitted this since it should be easy to
implement.
I have tested this on x86_64.
The interceptor library source:
/* Override recvfrom and modify the header of the first DNS response to make it
a referral and reproduce bz #845218. We have to resort to this ugly hack
because we cannot make bind return the buggy response of a referral for the
AAAA record and an authoritative response for the A record. */
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdbool.h>
#include <endian.h>
#include <dlfcn.h>
#include <stdlib.h>
/* Lifted from resolv/arpa/nameser_compat.h. */
typedef struct {
unsigned id :16; /*%< query identification number */
#if BYTE_ORDER == BIG_ENDIAN
/* fields in third byte */
unsigned qr: 1; /*%< response flag */
unsigned opcode: 4; /*%< purpose of message */
unsigned aa: 1; /*%< authoritive answer */
unsigned tc: 1; /*%< truncated message */
unsigned rd: 1; /*%< recursion desired */
/* fields
* in
* fourth
* byte
* */
unsigned ra: 1; /*%< recursion available */
unsigned unused :1; /*%< unused bits (MBZ as of 4.9.3a3) */
unsigned ad: 1; /*%< authentic data from named */
unsigned cd: 1; /*%< checking disabled by resolver */
unsigned rcode :4; /*%< response code */
#endif
#if BYTE_ORDER == LITTLE_ENDIAN || BYTE_ORDER == PDP_ENDIAN
/* fields
* in
* third
* byte
* */
unsigned rd :1; /*%< recursion desired */
unsigned tc :1; /*%< truncated message */
unsigned aa :1; /*%< authoritive answer */
unsigned opcode :4; /*%< purpose of message */
unsigned qr :1; /*%< response flag */
/* fields
* in
* fourth
* byte
* */
unsigned rcode :4; /*%< response code */
unsigned cd: 1; /*%< checking disabled by resolver */
unsigned ad: 1; /*%< authentic data from named */
unsigned unused :1; /*%< unused bits (MBZ as of 4.9.3a3) */
unsigned ra :1; /*%< recursion available */
#endif
/* remaining
* bytes
* */
unsigned qdcount :16; /*%< number of question entries */
unsigned ancount :16; /*%< number of answer entries */
unsigned nscount :16; /*%< number of authority entries */
unsigned arcount :16; /*%< number of resource entries */
} HEADER;
static int done = 0;
/* Packets to modify. 0 for the odd packets and 1 for even packets. */
static const int mod_packet = 0;
/* Set to true if the first request should result in an error, resulting in a
search query. */
static bool first_error = true;
static ssize_t (*real_recvfrom) (int sockfd, void *buf, size_t len, int flags,
struct sockaddr *src_addr, socklen_t *addrlen);
void
__attribute__ ((constructor))
init (void)
{
real_recvfrom = dlsym (RTLD_NEXT, "recvfrom");
if (real_recvfrom == NULL)
{
printf ("Failed to get reference to recvfrom: %s\n", dlerror ());
printf ("Cannot simulate test\n");
abort ();
}
}
/* Modify the second packet that we receive to set the header in a manner as to
reproduce BZ #845218. */
static void
mod_buf (HEADER *h, int port)
{
if (done % 2 == mod_packet || (first_error && done == 1))
{
printf ("(Modifying header)");
if (first_error && done == 1)
h->rcode = 3;
else
h->rcode = 0; /* NOERROR == 0. */
h->ancount = 0;
h->aa = 0;
h->ra = 0;
h->arcount = 0;
}
done++;
}
ssize_t
recvfrom (int sockfd, void *buf, size_t len, int flags,
struct sockaddr *src_addr, socklen_t *addrlen)
{
ssize_t ret = real_recvfrom (sockfd, buf, len, flags, src_addr, addrlen);
int port = htons (((struct sockaddr_in *) src_addr)->sin_port);
struct in_addr addr = ((struct sockaddr_in *) src_addr)->sin_addr;
const char *host = inet_ntoa (addr);
printf ("\n*** From %s:%d: ", host, port);
mod_buf (buf, port);
printf ("returned %zd\n", ret);
return ret;
}
ChangeLog | 11 +++++++++++
NEWS | 14 +++++++-------
resolv/res_query.c | 7 +++++--
resolv/res_send.c | 2 +-
4 files changed, 24 insertions(+), 10 deletions(-)
commit e35c53e397e7abbd41fedacdedcfa5af7b5c2c52
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date: Tue Jul 8 16:40:24 2014 +0530
Check value at resplen2 if it is not NULL
There was a typo in the previous patch due to which resplen2 was
checked for non-zero instead of the value at resplen2. Fix that and
improve the condition by checking resplen2 for non-NULL (instead of
answerp2) and also adding the check in a third place.
ChangeLog | 3 +++
resolv/res_query.c | 9 +++++----
2 files changed, 8 insertions(+), 4 deletions(-)
diff -pruN glibc-2.17-c758a686/resolv/res_query.c glibc-2.17-c758a686/resolv/res_query.c
--- glibc-2.17-c758a686/resolv/res_query.c 2012-12-25 08:32:13.000000000 +0530
+++ glibc-2.17-c758a686/resolv/res_query.c 2014-09-05 14:28:06.439191017 +0530
@@ -378,7 +378,9 @@ __libc_res_nsearch(res_state statp,
ret = __libc_res_nquerydomain(statp, name, NULL, class, type,
answer, anslen, answerp,
answerp2, nanswerp2, resplen2);
- if (ret > 0 || trailing_dot)
+ if (ret > 0 || trailing_dot
+ /* If the second response is valid then we use that. */
+ || (ret == 0 && resplen2 != NULL && *resplen2 > 0))
return (ret);
saved_herrno = h_errno;
tried_as_is++;
@@ -418,7 +420,8 @@ __libc_res_nsearch(res_state statp,
answer, anslen, answerp,
answerp2, nanswerp2,
resplen2);
- if (ret > 0)
+ if (ret > 0 || (ret == 0 && resplen2 != NULL
+ && *resplen2 > 0))
return (ret);
if (answerp && *answerp != answer) {
@@ -487,7 +490,8 @@ __libc_res_nsearch(res_state statp,
ret = __libc_res_nquerydomain(statp, name, NULL, class, type,
answer, anslen, answerp,
answerp2, nanswerp2, resplen2);
- if (ret > 0)
+ if (ret > 0 || (ret == 0 && resplen2 != NULL
+ && *resplen2 > 0))
return (ret);
}
diff -pruN glibc-2.17-c758a686/resolv/res_send.c glibc-2.17-c758a686/resolv/res_send.c
--- glibc-2.17-c758a686/resolv/res_send.c 2014-09-05 14:28:30.039337246 +0530
+++ glibc-2.17-c758a686/resolv/res_send.c 2014-09-05 14:28:06.439191017 +0530
@@ -1343,6 +1343,7 @@ send_dg(res_state statp,
(*thisresplenp > *thisanssizp)
? *thisanssizp : *thisresplenp);
+ next_ns:
if (recvresp1 || (buf2 != NULL && recvresp2)) {
*resplen2 = 0;
return resplen;
@@ -1360,7 +1361,6 @@ send_dg(res_state statp,
goto wait;
}
- next_ns:
__res_iclose(statp, false);
/* don't retry if called from dig */
if (!statp->pfcode)