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authorFlorian Weimer <fweimer@redhat.com>2016-04-22 10:38:15 -0500
committerPaul E. Murphy <murphyp@linux.vnet.ibm.com>2016-04-22 14:53:46 -0500
commit715e7fe0322004fd2e3fed853e9be3c279f5015d (patch)
tree88bc1c2842d3cd104846c665af76af3f506c0b8f
parent04130e53ba685dd7138e3e928708e17923f795b5 (diff)
downloadtermbaud-release/2.18/master.tar.gz
termbaud-release/2.18/master.tar.xz
termbaud-release/2.18/master.zip
resolv: Always set *resplen2 out parameter in send_dg [BZ #19791]release/2.18/master
Since commit 44d20bca52ace85850012b0ead37b360e3ecd96e (Implement second fallback mode for DNS requests), there is a code path which returns early, before *resplen2 is initialized. This happens if the name server address is immediately recognized as invalid (because of lack of protocol support, or if it is a broadcast address such 255.255.255.255, or another invalid address). If this happens and *resplen2 was non-zero (which is the case if a previous query resulted in a failure), __libc_res_nquery would reuse an existing second answer buffer. This answer has been previously identified as unusable (for example, it could be an NXDOMAIN response). Due to the presence of a second answer, no name server switching will occur. The result is a name resolution failure, although a successful resolution would have been possible if name servers have been switched and queries had proceeded along the search path. The above paragraph still simplifies the situation. Before glibc 2.23, if the second answer needed malloc, the stub resolver would still attempt to reuse the second answer, but this is not possible because __libc_res_nsearch has freed it, after the unsuccessful call to __libc_res_nquerydomain, and set the buffer pointer to NULL. This eventually leads to an assertion failure in __libc_res_nquery: /* Make sure both hp and hp2 are defined */ assert((hp != NULL) && (hp2 != NULL)); If assertions are disabled, the consequence is a NULL pointer dereference on the next line. Starting with glibc 2.23, as a result of commit e9db92d3acfe1822d56d11abcea5bfc4c41cf6ca (CVE-2015-7547: getaddrinfo() stack-based buffer overflow (Bug 18665)), the second answer is always allocated with malloc. This means that the assertion failure happens with small responses as well because there is no buffer to reuse, as soon as there is a name resolution failure which triggers a search for an answer along the search path. This commit addresses the issue by ensuring that *resplen2 is initialized before the send_dg function returns. This commit also addresses a bug where an invalid second reply is incorrectly returned as a valid to the caller. (cherry picked from commit b66d837bb5398795c6b0f651bd5a5d66091d8577)
-rw-r--r--ChangeLog9
-rw-r--r--NEWS3
-rw-r--r--resolv/res_send.c63
3 files changed, 51 insertions, 24 deletions
diff --git a/ChangeLog b/ChangeLog
index 0be4a594d7a..fb777de2668 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2016-04-22 Florian Weimer <fweimer@redhat.com>
+
+ [BZ #19791]
+ * resolv/res_send.c (close_and_return_error): New function.
+ (send_dg): Initialize *resplen2 after reopen failure. Call
+ close_and_return_error for error returns. On error paths without
+ __res_iclose, initialze *resplen2 explicitly. Update comment for
+ successful return.
+
2016-04-22 Andreas Schwab <schwab@suse.de>
[BZ #15946]
diff --git a/NEWS b/NEWS
index 94bcc4e54b3..67a29f8f277 100644
--- a/NEWS
+++ b/NEWS
@@ -10,7 +10,8 @@ Version 2.18.1
* The following bugs are resolved with this release:
15073, 15128, 15909, 15946, 15996, 16009, 16150, 16169, 16387, 16510,
- 16885, 16916, 16943, 16958, 17269, 18032, 18665, 18928, 19018.
+ 16885, 16916, 16943, 16958, 17269, 18032, 18665, 18928, 19018, 19791.
+
* The LD_POINTER_GUARD environment variable can no longer be used to
disable the pointer guard feature. It is always enabled.
diff --git a/resolv/res_send.c b/resolv/res_send.c
index e8b1809eab2..9a10ef4bd5b 100644
--- a/resolv/res_send.c
+++ b/resolv/res_send.c
@@ -671,6 +671,18 @@ libresolv_hidden_def (res_nsend)
/* Private */
+/* Close the resolver structure, assign zero to *RESPLEN2 if RESPLEN2
+ is not NULL, and return zero. */
+static int
+__attribute__ ((warn_unused_result))
+close_and_return_error (res_state statp, int *resplen2)
+{
+ __res_iclose(statp, false);
+ if (resplen2 != NULL)
+ *resplen2 = 0;
+ return 0;
+}
+
/* The send_vc function is responsible for sending a DNS query over TCP
to the nameserver numbered NS from the res_state STATP i.e.
EXT(statp).nssocks[ns]. The function supports sending both IPv4 and
@@ -1156,7 +1168,11 @@ send_dg(res_state statp,
retry_reopen:
retval = reopen (statp, terrno, ns);
if (retval <= 0)
- return retval;
+ {
+ if (resplen2 != NULL)
+ *resplen2 = 0;
+ return retval;
+ }
retry:
evNowTime(&now);
evConsTime(&timeout, seconds, 0);
@@ -1169,8 +1185,6 @@ send_dg(res_state statp,
int recvresp2 = buf2 == NULL;
pfd[0].fd = EXT(statp).nssocks[ns];
pfd[0].events = POLLOUT;
- if (resplen2 != NULL)
- *resplen2 = 0;
wait:
if (need_recompute) {
recompute_resend:
@@ -1178,9 +1192,7 @@ send_dg(res_state statp,
if (evCmpTime(finish, now) <= 0) {
poll_err_out:
Perror(statp, stderr, "poll", errno);
- err_out:
- __res_iclose(statp, false);
- return (0);
+ return close_and_return_error (statp, resplen2);
}
evSubTime(&timeout, &finish, &now);
need_recompute = 0;
@@ -1227,7 +1239,9 @@ send_dg(res_state statp,
}
*gotsomewhere = 1;
- return (0);
+ if (resplen2 != NULL)
+ *resplen2 = 0;
+ return 0;
}
if (n < 0) {
if (errno == EINTR)
@@ -1295,7 +1309,7 @@ send_dg(res_state statp,
fail_sendmmsg:
Perror(statp, stderr, "sendmmsg", errno);
- goto err_out;
+ return close_and_return_error (statp, resplen2);
}
}
else
@@ -1313,7 +1327,7 @@ send_dg(res_state statp,
if (errno == EINTR || errno == EAGAIN)
goto recompute_resend;
Perror(statp, stderr, "send", errno);
- goto err_out;
+ return close_and_return_error (statp, resplen2);
}
just_one:
if (nwritten != 0 || buf2 == NULL || single_request)
@@ -1389,7 +1403,7 @@ send_dg(res_state statp,
goto wait;
}
Perror(statp, stderr, "recvfrom", errno);
- goto err_out;
+ return close_and_return_error (statp, resplen2);
}
*gotsomewhere = 1;
if (__builtin_expect (*thisresplenp < HFIXEDSZ, 0)) {
@@ -1400,7 +1414,7 @@ send_dg(res_state statp,
(stdout, ";; undersized: %d\n",
*thisresplenp));
*terrno = EMSGSIZE;
- goto err_out;
+ return close_and_return_error (statp, resplen2);
}
if ((recvresp1 || hp->id != anhp->id)
&& (recvresp2 || hp2->id != anhp->id)) {
@@ -1449,7 +1463,7 @@ send_dg(res_state statp,
? *thisanssizp : *thisresplenp);
/* record the error */
statp->_flags |= RES_F_EDNS0ERR;
- goto err_out;
+ return close_and_return_error (statp, resplen2);
}
#endif
if (!(statp->options & RES_INSECURE2)
@@ -1501,10 +1515,10 @@ send_dg(res_state statp,
}
next_ns:
- __res_iclose(statp, false);
/* don't retry if called from dig */
if (!statp->pfcode)
- return (0);
+ return close_and_return_error (statp, resplen2);
+ __res_iclose(statp, false);
}
if (anhp->rcode == NOERROR && anhp->ancount == 0
&& anhp->aa == 0 && anhp->ra == 0 && anhp->arcount == 0) {
@@ -1526,6 +1540,8 @@ send_dg(res_state statp,
__res_iclose(statp, false);
// XXX if we have received one reply we could
// XXX use it and not repeat it over TCP...
+ if (resplen2 != NULL)
+ *resplen2 = 0;
return (1);
}
/* Mark which reply we received. */
@@ -1541,21 +1557,22 @@ send_dg(res_state statp,
__res_iclose (statp, false);
retval = reopen (statp, terrno, ns);
if (retval <= 0)
- return retval;
+ {
+ if (resplen2 != NULL)
+ *resplen2 = 0;
+ return retval;
+ }
pfd[0].fd = EXT(statp).nssocks[ns];
}
}
goto wait;
}
- /*
- * All is well, or the error is fatal. Signal that the
- * next nameserver ought not be tried.
- */
+ /* All is well. We have received both responses (if
+ two responses were requested). */
return (resplen);
- } else if (pfd[0].revents & (POLLERR | POLLHUP | POLLNVAL)) {
- /* Something went wrong. We can stop trying. */
- goto err_out;
- }
+ } else if (pfd[0].revents & (POLLERR | POLLHUP | POLLNVAL))
+ /* Something went wrong. We can stop trying. */
+ return close_and_return_error (statp, resplen2);
else {
/* poll should not have returned > 0 in this case. */
abort ();