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Overhaul extract_addresses() function.

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The proximate cause for doing this is to fix a bug that
causes replies to PTR queries with more than one answer to have the
second and subsequent answers ignored.

The fix turned into a small re-write which removed a very old hack.
When caching reponses which include CNAME records, the cache system
stores the CNAME with a link to the record representing the target of
the CNAME. This isn't possible for PTR records representing IP
addresses since the name stored is the target of the PTR, record and
its name is inferred from the address in the cache record. Such
cache records have the F_REVERSE flag set. To get
around this, long ago, the code which stores such records elided the
CNAME entirely, so
4.3.2.1.in-addr.arpa   CNAME 18/3.2.1.in-addr.arpa
18/3.2.1.in-addr.arpa   PTR   myhost.example.com

would be stored as
4.3.2.1.in-addr.arpa PTR   myhost.example.com

and returned from the cache to subsequent requestor in that form.

Since that hack was committed, dnsmasq has learned to cache arbitrary
RRs. So now we can store the PTR records for all the no-trivial cases.

The means the CNAME chains ending in PTR records don't get mangled,
and we can store PTR records whose name in not w.x.y.x.in-addr.arpa
or the IPv6 equivalent.
This commit is contained in:
Simon Kelley
2025-05-18 17:24:41 +01:00
parent 91b800cc62
commit e48a2af4f5
4 changed files with 82 additions and 141 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
src/dnsmasq.h
View File

@@ -1413,7 +1413,7 @@ unsigned int extract_request(struct dns_header *header, size_t qlen, char *name,
unsigned short *typep, unsigned short *classp);
void setup_reply(struct dns_header *header, unsigned int flags, int ede);
int extract_addresses(struct dns_header *header, size_t qlen, char *name,
time_t now, struct ipsets *ipsets, struct ipsets *nftsets, int is_sign,
time_t now, struct ipsets *ipsets, struct ipsets *nftsets,
int check_rebind, int no_cache_dnssec, int secure);
#if defined(HAVE_CONNTRACK) && defined(HAVE_UBUS)
void report_addresses(struct dns_header *header, size_t len, u32 mark);

2
src/forward.c
View File

@@ -819,7 +819,7 @@ static size_t process_reply(struct dns_header *header, time_t now, struct server
}
else
{
int rc = extract_addresses(header, n, daemon->namebuff, now, ipsets, nftsets, is_sign, check_rebind, no_cache, cache_secure);
int rc = extract_addresses(header, n, daemon->namebuff, now, ipsets, nftsets, check_rebind, no_cache, cache_secure);
if (rc != 0)
{

216
src/rfc1035.c
View File

@@ -687,12 +687,12 @@ static int log_txt(char *name, unsigned char *p, const int ardlen, int flag)
Return 2 if the packet is malformed.
*/
int extract_addresses(struct dns_header *header, size_t qlen, char *name, time_t now,
struct ipsets *ipsets, struct ipsets *nftsets, int is_sign, int check_rebind,
struct ipsets *ipsets, struct ipsets *nftsets, int check_rebind,
int no_cache_dnssec, int secure)
{
unsigned char *p, *p1, *endrr, *namep;
int j, qtype, qclass, aqtype, aqclass, ardlen, res;
unsigned long ttl = 0;
unsigned long ttl;
union all_addr addr;
#ifdef HAVE_IPSET
char **ipsets_cur;
@@ -704,13 +704,8 @@ int extract_addresses(struct dns_header *header, size_t qlen, char *name, time_t
#else
(void)nftsets; /* unused */
#endif
int found = 0, cname_count = CNAME_CHAIN;
struct crec *cpp = NULL;
int name_encoding, found = 0, ptr = 0;
int flags = RCODE(header) == NXDOMAIN ? F_NXDOMAIN : 0;
#ifdef HAVE_DNSSEC
int cname_short = 0;
#endif
unsigned long cttl = ULONG_MAX, attl;
cache_start_insert();
@@ -724,125 +719,73 @@ int extract_addresses(struct dns_header *header, size_t qlen, char *name, time_t
if (qclass != C_IN)
return 0;
/* PTRs: we chase CNAMEs here, since we have no way to
represent them in the cache. */
if (qtype == T_PTR)
/* If the PTR record encodes an address, store using a name/address record with F_REVERSE set.
Otherwise, it gets stored as an arbitrary RR below. If the query is answerable with
a CNAME, also take the arbitrary-RR route, since the cache can't represent a CNAME
whose target is stored in a F_REVERSE record. */
if (qtype == T_PTR && !(flags & F_NXDOMAIN) && (name_encoding = in_arpa_name_2_addr(name, &addr)))
{
int insert = 1, name_encoding = in_arpa_name_2_addr(name, &addr);
ptr = 1;
if (!(flags & F_NXDOMAIN))
if (!(p1 = skip_questions(header, qlen)))
return 2;
for (j = 0; j < ntohs(header->ancount); j++)
{
cname_loop:
if (!(p1 = skip_questions(header, qlen)))
return 2;
int secflag = 0;
if (!(res = extract_name(header, qlen, &p1, name, EXTR_NAME_COMPARE, 10)))
return 2; /* bad packet */
for (j = 0; j < ntohs(header->ancount); j++)
GETSHORT(aqtype, p1);
GETSHORT(aqclass, p1);
p = p1;
GETLONG(ttl, p1);
GETSHORT(ardlen, p1);
endrr = p1+ardlen;
if (aqclass == C_IN && res == 1 && aqtype == T_PTR)
{
int secflag = 0;
if (!(res = extract_name(header, qlen, &p1, name, EXTR_NAME_COMPARE, 10)))
return 2; /* bad packet */
found = 1;
if ((daemon->max_ttl != 0) && (ttl > daemon->max_ttl))
ttl = daemon->max_ttl;
GETSHORT(aqtype, p1);
GETSHORT(aqclass, p1);
GETLONG(attl, p1);
if ((daemon->max_ttl != 0) && (attl > daemon->max_ttl) && !is_sign)
{
(p1) -= 4;
PUTLONG(daemon->max_ttl, p1);
}
GETSHORT(ardlen, p1);
endrr = p1+ardlen;
/* TTL of record is minimum of CNAMES and PTR */
if (attl < cttl)
cttl = attl;
if (aqclass == C_IN && res != 2 && (aqtype == T_CNAME || aqtype == T_PTR))
{
#ifdef HAVE_DNSSEC
if (option_bool(OPT_DNSSEC_VALID) && j < daemon->rr_status_sz && daemon->rr_status[j] != 0)
{
/* validated RR anywhere in CNAME chain, don't cache. */
if (cname_short || aqtype == T_CNAME)
insert = 0;
secflag = F_DNSSECOK;
/* limit TTL based on signature. */
if (daemon->rr_status[j] < cttl)
cttl = daemon->rr_status[j];
}
#endif
if (aqtype == T_CNAME)
log_query(secflag | F_CNAME | F_FORWARD | F_UPSTREAM, name, NULL, NULL, 0);
if (!extract_name(header, qlen, &p1, name, EXTR_NAME_EXTRACT, 0))
return 2;
if (aqtype == T_CNAME)
{
if (!cname_count--)
return 0; /* looped CNAMES, we can't cache. */
#ifdef HAVE_DNSSEC
cname_short = 1;
#endif
goto cname_loop;
}
found = 1;
if (!name_encoding)
log_query(secflag | F_FORWARD | F_UPSTREAM, name, NULL, NULL, aqtype);
else
{
log_query(name_encoding | secflag | F_REVERSE | F_UPSTREAM, name, &addr, NULL, 0);
if (insert)
cache_insert(name, &addr, C_IN, now, cttl, name_encoding | secflag | F_REVERSE);
}
}
p1 = endrr;
if (!CHECK_LEN(header, p1, qlen, 0))
return 2; /* bad packet */
}
}
if (!found)
{
flags |= F_NEG | (secure ? F_DNSSECOK : 0);
if (name_encoding)
flags |= F_REVERSE | name_encoding;
log_query(flags | F_UPSTREAM, name, &addr, NULL, 0);
if (name_encoding && !option_bool(OPT_NO_NEG))
{
/* For reverse records, we use the name field to store the SOA name. */
int substring, have_soa = find_soa(header, qlen, name, &substring, &ttl, no_cache_dnssec, now);
if (have_soa || daemon->neg_ttl)
if (option_bool(OPT_DNSSEC_VALID) && j < daemon->rr_status_sz && daemon->rr_status[j] != 0)
{
/* If daemon->neg_ttl is set, we can cache even without an SOA. */
if (!have_soa)
{
flags |= F_NO_RR; /* Marks no SOA found. */
ttl = daemon->neg_ttl;
}
cache_insert(name + substring, &addr, C_IN, now, ttl, flags);
secflag = F_DNSSECOK;
/* limit TTL based on signature. */
if (daemon->rr_status[j] < ttl)
ttl = daemon->rr_status[j];
}
#endif
PUTLONG(ttl, p);
if (!extract_name(header, qlen, &p1, name, EXTR_NAME_EXTRACT, 0))
return 2;
log_query(name_encoding | secflag | F_REVERSE | F_UPSTREAM, name, &addr, NULL, 0);
cache_insert(name, &addr, C_IN, now, ttl, name_encoding | secflag | F_REVERSE);
/* restore query into name */
p1 = namep;
if (!extract_name(header, qlen, &p1, name, EXTR_NAME_EXTRACT, 0))
return 2;
}
p1 = endrr;
if (!CHECK_LEN(header, p1, qlen, 0))
return 2; /* bad packet */
}
}
else
if (!ptr || !found)
{
/* everything other than PTR */
struct crec *newc;
int addrlen = 0, insert = 1;
struct crec *newc, *cpp = NULL;
int cname_count = CNAME_CHAIN, addrlen = 0, insert = 1;
if (qtype == T_A)
{
addrlen = INADDRSZ;
@@ -854,12 +797,12 @@ int extract_addresses(struct dns_header *header, size_t qlen, char *name, time_t
flags |= F_IPV6;
}
else if (qtype != T_CNAME &&
(qtype == T_SRV || rr_on_list(daemon->cache_rr, qtype) || rr_on_list(daemon->cache_rr, T_ANY)))
(qtype == T_SRV || qtype == T_PTR || rr_on_list(daemon->cache_rr, qtype) || rr_on_list(daemon->cache_rr, T_ANY)))
flags |= F_RR;
else
insert = 0; /* NOTE: do not cache data from CNAME queries. */
cname_loop1:
cname_loop:
if (!(p1 = skip_questions(header, qlen)))
return 2;
@@ -872,12 +815,8 @@ int extract_addresses(struct dns_header *header, size_t qlen, char *name, time_t
GETSHORT(aqtype, p1);
GETSHORT(aqclass, p1);
GETLONG(attl, p1);
if ((daemon->max_ttl != 0) && (attl > daemon->max_ttl) && !is_sign)
{
(p1) -= 4;
PUTLONG(daemon->max_ttl, p1);
}
p = p1;
GETLONG(ttl, p1);
GETSHORT(ardlen, p1);
endrr = p1+ardlen;
@@ -890,6 +829,9 @@ int extract_addresses(struct dns_header *header, size_t qlen, char *name, time_t
p1 = endrr;
continue;
}
if ((daemon->max_ttl != 0) && (ttl > daemon->max_ttl))
ttl = daemon->max_ttl;
#ifdef HAVE_DNSSEC
if (option_bool(OPT_DNSSEC_VALID) && j < daemon->rr_status_sz && daemon->rr_status[j] != 0)
@@ -897,10 +839,12 @@ int extract_addresses(struct dns_header *header, size_t qlen, char *name, time_t
secflag = F_DNSSECOK;
/* limit TTl based on sig. */
if (daemon->rr_status[j] < attl)
attl = daemon->rr_status[j];
if (daemon->rr_status[j] < ttl)
ttl = daemon->rr_status[j];
}
#endif
PUTLONG(ttl, p);
if (aqtype == T_CNAME)
{
@@ -911,7 +855,7 @@ int extract_addresses(struct dns_header *header, size_t qlen, char *name, time_t
if (insert)
{
if ((newc = cache_insert(name, NULL, C_IN, now, attl, F_CNAME | F_FORWARD | secflag)))
if ((newc = cache_insert(name, NULL, C_IN, now, ttl, F_CNAME | F_FORWARD | secflag)))
{
newc->addr.cname.target.cache = NULL;
newc->addr.cname.is_name_ptr = 0;
@@ -924,16 +868,15 @@ int extract_addresses(struct dns_header *header, size_t qlen, char *name, time_t
}
cpp = newc;
if (attl < cttl)
cttl = attl;
}
/* Set the query to the CNAME target and go again unless the query was just for a CNAME. */
namep = p1;
if (!extract_name(header, qlen, &p1, name, EXTR_NAME_EXTRACT, 0))
return 2;
if (qtype != T_CNAME)
goto cname_loop1;
goto cname_loop;
found = 1;
}
@@ -1089,7 +1032,7 @@ int extract_addresses(struct dns_header *header, size_t qlen, char *name, time_t
if (insert)
{
newc = cache_insert(name, &addr, C_IN, now, attl, flags | F_FORWARD | secflag);
newc = cache_insert(name, &addr, C_IN, now, ttl, flags | F_FORWARD | secflag);
if (newc && cpp)
{
next_uid(newc);
@@ -1668,7 +1611,7 @@ size_t answer_request(struct dns_header *header, char *limit, size_t qlen,
int rd_bit = (header->hb3 & HB3_RD);
int count = 255; /* catch loops */
/* Suppress cached answers of no_cache set. */
/* Suppress cached answers if no_cache set. */
if (no_cache)
rd_bit = 0;
@@ -1678,14 +1621,12 @@ size_t answer_request(struct dns_header *header, char *limit, size_t qlen,
if (filtered)
*filtered = 0;
/* never answer queries with RD unset, to avoid cache snooping. */
if ( ntohs(header->qdcount) != 1 ||
ntohs(header->ancount) != 0 ||
if (ntohs(header->qdcount) != 1 ||
ntohs(header->ancount) != 0 ||
ntohs(header->nscount) != 0 ||
ntohs(header->qdcount) == 0 ||
OPCODE(header) != QUERY )
return 0;
/* Don't return AD set if checking disabled. */
if (header->hb4 & HB4_CD)
sec_data = 0;
@@ -2348,14 +2289,11 @@ size_t answer_request(struct dns_header *header, char *limit, size_t qlen,
For FORWARD NEG records, the addr.rrdata.datalen field of the othewise
empty addr is used to held an offset in to the name which yields the SOA
name. For REVERSE NEG records, the otherwise empty name field holds the
SOA name. If soa_name has zero length, then no SOA is known. soa_lookup
MUST be a neg record here.
name.
If the F_NO_RR flag is set, there was no SOA record supplied with the RR. */
if (soa_lookup && !(soa_lookup->flags & F_NO_RR))
{
char *soa_name = soa_lookup->flags & F_REVERSE ? cache_get_name(soa_lookup) : name + soa_lookup->addr.rrdata.datalen;
char *soa_name = name + soa_lookup->addr.rrdata.datalen;
crecp = NULL;
while ((crecp = cache_find_by_name(crecp, soa_name, now, F_RR)))