int h_namelen = 0;
if (ancount == 0)
- return NSS_STATUS_NOTFOUND;
+ {
+ *h_errnop = HOST_NOT_FOUND;
+ return NSS_STATUS_NOTFOUND;
+ }
while (ancount-- > 0 && cp < end_of_message && had_error == 0)
{
/* Special case here: if the resolver sent a result but it only
contains a CNAME while we are looking for a T_A or T_AAAA record,
we fail with NOTFOUND instead of TRYAGAIN. */
- return canon == NULL ? NSS_STATUS_TRYAGAIN : NSS_STATUS_NOTFOUND;
+ if (canon != NULL)
+ {
+ *h_errnop = HOST_NOT_FOUND;
+ return NSS_STATUS_NOTFOUND;
+ }
+
+ *h_errnop = NETDB_INTERNAL;
+ return NSS_STATUS_TRYAGAIN;
}
enum nss_status status = NSS_STATUS_NOTFOUND;
+ /* Combining the NSS status of two distinct queries requires some
+ compromise and attention to symmetry (A or AAAA queries can be
+ returned in any order). What follows is a breakdown of how this
+ code is expected to work and why. We discuss only SUCCESS,
+ TRYAGAIN, NOTFOUND and UNAVAIL, since they are the only returns
+ that apply (though RETURN and MERGE exist). We make a distinction
+ between TRYAGAIN (recoverable) and TRYAGAIN' (not-recoverable).
+ A recoverable TRYAGAIN is almost always due to buffer size issues
+ and returns ERANGE in errno and the caller is expected to retry
+ with a larger buffer.
+
+ Lastly, you may be tempted to make significant changes to the
+ conditions in this code to bring about symmetry between responses.
+ Please don't change anything without due consideration for
+ expected application behaviour. Some of the synthesized responses
+ aren't very well thought out and sometimes appear to imply that
+ IPv4 responses are always answer 1, and IPv6 responses are always
+ answer 2, but that's not true (see the implementation of send_dg
+ and send_vc to see response can arrive in any order, particularly
+ for UDP). However, we expect it holds roughly enough of the time
+ that this code works, but certainly needs to be fixed to make this
+ a more robust implementation.
+
+ ----------------------------------------------
+ | Answer 1 Status / | Synthesized | Reason |
+ | Answer 2 Status | Status | |
+ |--------------------------------------------|
+ | SUCCESS/SUCCESS | SUCCESS | [1] |
+ | SUCCESS/TRYAGAIN | TRYAGAIN | [5] |
+ | SUCCESS/TRYAGAIN' | SUCCESS | [1] |
+ | SUCCESS/NOTFOUND | SUCCESS | [1] |
+ | SUCCESS/UNAVAIL | SUCCESS | [1] |
+ | TRYAGAIN/SUCCESS | TRYAGAIN | [2] |
+ | TRYAGAIN/TRYAGAIN | TRYAGAIN | [2] |
+ | TRYAGAIN/TRYAGAIN' | TRYAGAIN | [2] |
+ | TRYAGAIN/NOTFOUND | TRYAGAIN | [2] |
+ | TRYAGAIN/UNAVAIL | TRYAGAIN | [2] |
+ | TRYAGAIN'/SUCCESS | SUCCESS | [3] |
+ | TRYAGAIN'/TRYAGAIN | TRYAGAIN | [3] |
+ | TRYAGAIN'/TRYAGAIN' | TRYAGAIN' | [3] |
+ | TRYAGAIN'/NOTFOUND | TRYAGAIN' | [3] |
+ | TRYAGAIN'/UNAVAIL | UNAVAIL | [3] |
+ | NOTFOUND/SUCCESS | SUCCESS | [3] |
+ | NOTFOUND/TRYAGAIN | TRYAGAIN | [3] |
+ | NOTFOUND/TRYAGAIN' | TRYAGAIN' | [3] |
+ | NOTFOUND/NOTFOUND | NOTFOUND | [3] |
+ | NOTFOUND/UNAVAIL | UNAVAIL | [3] |
+ | UNAVAIL/SUCCESS | UNAVAIL | [4] |
+ | UNAVAIL/TRYAGAIN | UNAVAIL | [4] |
+ | UNAVAIL/TRYAGAIN' | UNAVAIL | [4] |
+ | UNAVAIL/NOTFOUND | UNAVAIL | [4] |
+ | UNAVAIL/UNAVAIL | UNAVAIL | [4] |
+ ----------------------------------------------
+
+ [1] If the first response is a success we return success.
+ This ignores the state of the second answer and in fact
+ incorrectly sets errno and h_errno to that of the second
+ answer. However because the response is a success we ignore
+ *errnop and *h_errnop (though that means you touched errno on
+ success). We are being conservative here and returning the
+ likely IPv4 response in the first answer as a success.
+
+ [2] If the first response is a recoverable TRYAGAIN we return
+ that instead of looking at the second response. The
+ expectation here is that we have failed to get an IPv4 response
+ and should retry both queries.
+
+ [3] If the first response was not a SUCCESS and the second
+ response is not NOTFOUND (had a SUCCESS, need to TRYAGAIN,
+ or failed entirely e.g. TRYAGAIN' and UNAVAIL) then use the
+ result from the second response, otherwise the first responses
+ status is used. Again we have some odd side-effects when the
+ second response is NOTFOUND because we overwrite *errnop and
+ *h_errnop that means that a first answer of NOTFOUND might see
+ its *errnop and *h_errnop values altered. Whether it matters
+ in practice that a first response NOTFOUND has the wrong
+ *errnop and *h_errnop is undecided.
+
+ [4] If the first response is UNAVAIL we return that instead of
+ looking at the second response. The expectation here is that
+ it will have failed similarly e.g. configuration failure.
+
+ [5] Testing this code is complicated by the fact that truncated
+ second response buffers might be returned as SUCCESS if the
+ first answer is a SUCCESS. To fix this we add symmetry to
+ TRYAGAIN with the second response. If the second response
+ is a recoverable error we now return TRYAGIN even if the first
+ response was SUCCESS. */
+
if (anslen1 > 0)
status = gaih_getanswer_slice(answer1, anslen1, qname,
&pat, &buffer, &buflen,
errnop, h_errnop, ttlp,
&first);
+
if ((status == NSS_STATUS_SUCCESS || status == NSS_STATUS_NOTFOUND
|| (status == NSS_STATUS_TRYAGAIN
/* We want to look at the second answer in case of an
&pat, &buffer, &buflen,
errnop, h_errnop, ttlp,
&first);
+ /* Use the second response status in some cases. */
if (status != NSS_STATUS_SUCCESS && status2 != NSS_STATUS_NOTFOUND)
status = status2;
+ /* Do not return a truncated second response (unless it was
+ unavoidable e.g. unrecoverable TRYAGAIN). */
+ if (status == NSS_STATUS_SUCCESS
+ && (status2 == NSS_STATUS_TRYAGAIN
+ && *errnop == ERANGE && *h_errnop != NO_RECOVERY))
+ status = NSS_STATUS_TRYAGAIN;
}
return status;
+/* Copyright (C) 2016 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
/*
* Copyright (c) 1985, 1989, 1993
* The Regents of the University of California. All rights reserved.
#ifdef USE_HOOKS
if (__glibc_unlikely (statp->qhook || statp->rhook)) {
if (anssiz < MAXPACKET && ansp) {
+ /* Always allocate MAXPACKET, callers expect
+ this specific size. */
u_char *buf = malloc (MAXPACKET);
if (buf == NULL)
return (-1);
return (struct sockaddr *) (void *) &statp->nsaddr_list[n];
}
+/* 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
+ IPv6 queries at the same serially on the same socket.
+
+ Please note that for TCP there is no way to disable sending both
+ queries, unlike UDP, which honours RES_SNGLKUP and RES_SNGLKUPREOP
+ and sends the queries serially and waits for the result after each
+ sent query. This implemetnation should be corrected to honour these
+ options.
+
+ Please also note that for TCP we send both queries over the same
+ socket one after another. This technically violates best practice
+ since the server is allowed to read the first query, respond, and
+ then close the socket (to service another client). If the server
+ does this, then the remaining second query in the socket data buffer
+ will cause the server to send the client an RST which will arrive
+ asynchronously and the client's OS will likely tear down the socket
+ receive buffer resulting in a potentially short read and lost
+ response data. This will force the client to retry the query again,
+ and this process may repeat until all servers and connection resets
+ are exhausted and then the query will fail. It's not known if this
+ happens with any frequency in real DNS server implementations. This
+ implementation should be corrected to use two sockets by default for
+ parallel queries.
+
+ The query stored in BUF of BUFLEN length is sent first followed by
+ the query stored in BUF2 of BUFLEN2 length. Queries are sent
+ serially on the same socket.
+
+ Answers to the query are stored firstly in *ANSP up to a max of
+ *ANSSIZP bytes. If more than *ANSSIZP bytes are needed and ANSCP
+ is non-NULL (to indicate that modifying the answer buffer is allowed)
+ then malloc is used to allocate a new response buffer and ANSCP and
+ ANSP will both point to the new buffer. If more than *ANSSIZP bytes
+ are needed but ANSCP is NULL, then as much of the response as
+ possible is read into the buffer, but the results will be truncated.
+ When truncation happens because of a small answer buffer the DNS
+ packets header field TC will bet set to 1, indicating a truncated
+ message and the rest of the socket data will be read and discarded.
+
+ Answers to the query are stored secondly in *ANSP2 up to a max of
+ *ANSSIZP2 bytes, with the actual response length stored in
+ *RESPLEN2. If more than *ANSSIZP bytes are needed and ANSP2
+ is non-NULL (required for a second query) then malloc is used to
+ allocate a new response buffer, *ANSSIZP2 is set to the new buffer
+ size and *ANSP2_MALLOCED is set to 1.
+
+ The ANSP2_MALLOCED argument will eventually be removed as the
+ change in buffer pointer can be used to detect the buffer has
+ changed and that the caller should use free on the new buffer.
+
+ Note that the answers may arrive in any order from the server and
+ therefore the first and second answer buffers may not correspond to
+ the first and second queries.
+
+ It is not supported to call this function with a non-NULL ANSP2
+ but a NULL ANSCP. Put another way, you can call send_vc with a
+ single unmodifiable buffer or two modifiable buffers, but no other
+ combination is supported.
+
+ It is the caller's responsibility to free the malloc allocated
+ buffers by detecting that the pointers have changed from their
+ original values i.e. *ANSCP or *ANSP2 has changed.
+
+ If errors are encountered then *TERRNO is set to an appropriate
+ errno value and a zero result is returned for a recoverable error,
+ and a less-than zero result is returned for a non-recoverable error.
+
+ If no errors are encountered then *TERRNO is left unmodified and
+ a the length of the first response in bytes is returned. */
static int
send_vc(res_state statp,
const u_char *buf, int buflen, const u_char *buf2, int buflen2,
{
const HEADER *hp = (HEADER *) buf;
const HEADER *hp2 = (HEADER *) buf2;
- u_char *ans = *ansp;
- int orig_anssizp = *anssizp;
- // XXX REMOVE
- // int anssiz = *anssizp;
- HEADER *anhp = (HEADER *) ans;
+ HEADER *anhp = (HEADER *) *ansp;
struct sockaddr *nsap = get_nsaddr (statp, ns);
int truncating, connreset, n;
/* On some architectures compiler might emit a warning indicating
* Receive length & response
*/
int recvresp1 = 0;
+ /* Skip the second response if there is no second query.
+ To do that we mark the second response as received. */
int recvresp2 = buf2 == NULL;
uint16_t rlen16;
read_len:
u_char **thisansp;
int *thisresplenp;
if ((recvresp1 | recvresp2) == 0 || buf2 == NULL) {
+ /* We have not received any responses
+ yet or we only have one response to
+ receive. */
thisanssizp = anssizp;
thisansp = anscp ?: ansp;
assert (anscp != NULL || ansp2 == NULL);
thisresplenp = &resplen;
} else {
- if (*anssizp != MAXPACKET) {
- /* No buffer allocated for the first
- reply. We can try to use the rest
- of the user-provided buffer. */
- DIAG_PUSH_NEEDS_COMMENT;
- DIAG_IGNORE_NEEDS_COMMENT (5, "-Wmaybe-uninitialized");
-#if _STRING_ARCH_unaligned
- *anssizp2 = orig_anssizp - resplen;
- *ansp2 = *ansp + resplen;
-#else
- int aligned_resplen
- = ((resplen + __alignof__ (HEADER) - 1)
- & ~(__alignof__ (HEADER) - 1));
- *anssizp2 = orig_anssizp - aligned_resplen;
- *ansp2 = *ansp + aligned_resplen;
-#endif
- DIAG_POP_NEEDS_COMMENT;
- } else {
- /* The first reply did not fit into the
- user-provided buffer. Maybe the second
- answer will. */
- *anssizp2 = orig_anssizp;
- *ansp2 = *ansp;
- }
-
thisanssizp = anssizp2;
thisansp = ansp2;
thisresplenp = resplen2;
anhp = (HEADER *) *thisansp;
*thisresplenp = rlen;
- if (rlen > *thisanssizp) {
- /* Yes, we test ANSCP here. If we have two buffers
- both will be allocatable. */
- if (__glibc_likely (anscp != NULL)) {
+ /* Is the answer buffer too small? */
+ if (*thisanssizp < rlen) {
+ /* If the current buffer is not the the static
+ user-supplied buffer then we can reallocate
+ it. */
+ if (thisansp != NULL && thisansp != ansp) {
+ /* Always allocate MAXPACKET, callers expect
+ this specific size. */
u_char *newp = malloc (MAXPACKET);
if (newp == NULL) {
*terrno = ENOMEM;
if (thisansp == ansp2)
*ansp2_malloced = 1;
anhp = (HEADER *) newp;
+ /* A uint16_t can't be larger than MAXPACKET
+ thus it's safe to allocate MAXPACKET but
+ read RLEN bytes instead. */
len = rlen;
} else {
Dprint(statp->options & RES_DEBUG,
return 1;
}
+/* The send_dg function is responsible for sending a DNS query over UDP
+ to the nameserver numbered NS from the res_state STATP i.e.
+ EXT(statp).nssocks[ns]. The function supports IPv4 and IPv6 queries
+ along with the ability to send the query in parallel for both stacks
+ (default) or serially (RES_SINGLKUP). It also supports serial lookup
+ with a close and reopen of the socket used to talk to the server
+ (RES_SNGLKUPREOP) to work around broken name servers.
+
+ The query stored in BUF of BUFLEN length is sent first followed by
+ the query stored in BUF2 of BUFLEN2 length. Queries are sent
+ in parallel (default) or serially (RES_SINGLKUP or RES_SNGLKUPREOP).
+
+ Answers to the query are stored firstly in *ANSP up to a max of
+ *ANSSIZP bytes. If more than *ANSSIZP bytes are needed and ANSCP
+ is non-NULL (to indicate that modifying the answer buffer is allowed)
+ then malloc is used to allocate a new response buffer and ANSCP and
+ ANSP will both point to the new buffer. If more than *ANSSIZP bytes
+ are needed but ANSCP is NULL, then as much of the response as
+ possible is read into the buffer, but the results will be truncated.
+ When truncation happens because of a small answer buffer the DNS
+ packets header field TC will bet set to 1, indicating a truncated
+ message, while the rest of the UDP packet is discarded.
+
+ Answers to the query are stored secondly in *ANSP2 up to a max of
+ *ANSSIZP2 bytes, with the actual response length stored in
+ *RESPLEN2. If more than *ANSSIZP bytes are needed and ANSP2
+ is non-NULL (required for a second query) then malloc is used to
+ allocate a new response buffer, *ANSSIZP2 is set to the new buffer
+ size and *ANSP2_MALLOCED is set to 1.
+
+ The ANSP2_MALLOCED argument will eventually be removed as the
+ change in buffer pointer can be used to detect the buffer has
+ changed and that the caller should use free on the new buffer.
+
+ Note that the answers may arrive in any order from the server and
+ therefore the first and second answer buffers may not correspond to
+ the first and second queries.
+
+ It is not supported to call this function with a non-NULL ANSP2
+ but a NULL ANSCP. Put another way, you can call send_vc with a
+ single unmodifiable buffer or two modifiable buffers, but no other
+ combination is supported.
+
+ It is the caller's responsibility to free the malloc allocated
+ buffers by detecting that the pointers have changed from their
+ original values i.e. *ANSCP or *ANSP2 has changed.
+
+ If an answer is truncated because of UDP datagram DNS limits then
+ *V_CIRCUIT is set to 1 and the return value non-zero to indicate to
+ the caller to retry with TCP. The value *GOTSOMEWHERE is set to 1
+ if any progress was made reading a response from the nameserver and
+ is used by the caller to distinguish between ECONNREFUSED and
+ ETIMEDOUT (the latter if *GOTSOMEWHERE is 1).
+
+ If errors are encountered then *TERRNO is set to an appropriate
+ errno value and a zero result is returned for a recoverable error,
+ and a less-than zero result is returned for a non-recoverable error.
+
+ If no errors are encountered then *TERRNO is left unmodified and
+ a the length of the first response in bytes is returned. */
static int
send_dg(res_state statp,
const u_char *buf, int buflen, const u_char *buf2, int buflen2,
{
const HEADER *hp = (HEADER *) buf;
const HEADER *hp2 = (HEADER *) buf2;
- u_char *ans = *ansp;
- int orig_anssizp = *anssizp;
struct timespec now, timeout, finish;
struct pollfd pfd[1];
int ptimeout;
int need_recompute = 0;
int nwritten = 0;
int recvresp1 = 0;
+ /* Skip the second response if there is no second query.
+ To do that we mark the second response as received. */
int recvresp2 = buf2 == NULL;
pfd[0].fd = EXT(statp).nssocks[ns];
pfd[0].events = POLLOUT;
int *thisresplenp;
if ((recvresp1 | recvresp2) == 0 || buf2 == NULL) {
+ /* We have not received any responses
+ yet or we only have one response to
+ receive. */
thisanssizp = anssizp;
thisansp = anscp ?: ansp;
assert (anscp != NULL || ansp2 == NULL);
thisresplenp = &resplen;
} else {
- if (*anssizp != MAXPACKET) {
- /* No buffer allocated for the first
- reply. We can try to use the rest
- of the user-provided buffer. */
-#if _STRING_ARCH_unaligned
- *anssizp2 = orig_anssizp - resplen;
- *ansp2 = *ansp + resplen;
-#else
- int aligned_resplen
- = ((resplen + __alignof__ (HEADER) - 1)
- & ~(__alignof__ (HEADER) - 1));
- *anssizp2 = orig_anssizp - aligned_resplen;
- *ansp2 = *ansp + aligned_resplen;
-#endif
- } else {
- /* The first reply did not fit into the
- user-provided buffer. Maybe the second
- answer will. */
- *anssizp2 = orig_anssizp;
- *ansp2 = *ansp;
- }
-
thisanssizp = anssizp2;
thisansp = ansp2;
thisresplenp = resplen2;
}
if (*thisanssizp < MAXPACKET
- /* Yes, we test ANSCP here. If we have two buffers
- both will be allocatable. */
- && anscp
+ /* If the current buffer is not the the static
+ user-supplied buffer then we can reallocate
+ it. */
+ && (thisansp != NULL && thisansp != ansp)
#ifdef FIONREAD
+ /* Is the size too small? */
&& (ioctl (pfd[0].fd, FIONREAD, thisresplenp) < 0
|| *thisanssizp < *thisresplenp)
#endif
) {
+ /* Always allocate MAXPACKET, callers expect
+ this specific size. */
u_char *newp = malloc (MAXPACKET);
if (newp != NULL) {
- *anssizp = MAXPACKET;
- *thisansp = ans = newp;
+ *thisanssizp = MAXPACKET;
+ *thisansp = newp;
if (thisansp == ansp2)
*ansp2_malloced = 1;
}
}
+ /* We could end up with truncation if anscp was NULL
+ (not allowed to change caller's buffer) and the
+ response buffer size is too small. This isn't a
+ reliable way to detect truncation because the ioctl
+ may be an inaccurate report of the UDP message size.
+ Therefore we use this only to issue debug output.
+ To do truncation accurately with UDP we need
+ MSG_TRUNC which is only available on Linux. We
+ can abstract out the Linux-specific feature in the
+ future to detect truncation. */
+ if (__glibc_unlikely (*thisanssizp < *thisresplenp)) {
+ Dprint(statp->options & RES_DEBUG,
+ (stdout, ";; response may be truncated (UDP)\n")
+ );
+ }
+
HEADER *anhp = (HEADER *) *thisansp;
socklen_t fromlen = sizeof(struct sockaddr_in6);
assert (sizeof(from) <= fromlen);
git://sourceware.org / glibc.git / commitdiff