| From 5a56e1b78a753d3295564daddc9ce389cc69fd68 Mon Sep 17 00:00:00 2001 |
| From: Simon Kelley <simon@thekelleys.org.uk> |
| Date: Fri, 19 Jan 2018 12:26:08 +0000 |
| Subject: [PATCH] DNSSEC fix for wildcard NSEC records. CVE-2017-15107 applies. |
| |
| It's OK for NSEC records to be expanded from wildcards, |
| but in that case, the proof of non-existence is only valid |
| starting at the wildcard name, *.<domain> NOT the name expanded |
| from the wildcard. Without this check it's possible for an |
| attacker to craft an NSEC which wrongly proves non-existence |
| in a domain which includes a wildcard for NSEC. |
| |
| Upstream-Status: Backport [http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=4fe6744a220eddd3f1749b40cac3dfc510787de6] |
| CVE: CVE-2017-15107 |
| Signed-off-by: Sinan Kaya <okaya@kernel.org> |
| --- |
| CHANGELOG | 44 +++++++++++++++++++ |
| src/dnssec.c | 117 +++++++++++++++++++++++++++++++++++++++++++++------ |
| 2 files changed, 147 insertions(+), 14 deletions(-) |
| |
| diff --git a/CHANGELOG b/CHANGELOG |
| index 075fe1a6..5226dce8 100644 |
| --- a/CHANGELOG |
| +++ b/CHANGELOG |
| @@ -1,3 +1,47 @@ |
| +version 2.79 |
| + Fix parsing of CNAME arguments, which are confused by extra spaces. |
| + Thanks to Diego Aguirre for spotting the bug. |
| + |
| + Where available, use IP_UNICAST_IF or IPV6_UNICAST_IF to bind |
| + upstream servers to an interface, rather than SO_BINDTODEVICE. |
| + Thanks to Beniamino Galvani for the patch. |
| + |
| + Always return a SERVFAIL answer to DNS queries without the |
| + recursion desired bit set, UNLESS acting as an authoritative |
| + DNS server. This avoids a potential route to cache snooping. |
| + |
| + Add support for Ed25519 signatures in DNSSEC validation. |
| + |
| + No longer support RSA/MD5 signatures in DNSSEC validation, |
| + since these are not secure. This behaviour is mandated in |
| + RFC-6944. |
| + |
| + Fix incorrect error exit code from dhcp_release6 utility. |
| + Thanks Gaudenz Steinlin for the bug report. |
| + |
| + Use SIGINT (instead of overloading SIGHUP) to turn on DNSSEC |
| + time validation when --dnssec-no-timecheck is in use. |
| + Note that this is an incompatible change from earlier releases. |
| + |
| + Allow more than one --bridge-interface option to refer to an |
| + interface, so that we can use |
| + --bridge-interface=int1,alias1 |
| + --bridge-interface=int1,alias2 |
| + as an alternative to |
| + --bridge-interface=int1,alias1,alias2 |
| + Thanks to Neil Jerram for work on this. |
| + |
| + Fix for DNSSEC with wildcard-derived NSEC records. |
| + It's OK for NSEC records to be expanded from wildcards, |
| + but in that case, the proof of non-existence is only valid |
| + starting at the wildcard name, *.<domain> NOT the name expanded |
| + from the wildcard. Without this check it's possible for an |
| + attacker to craft an NSEC which wrongly proves non-existence. |
| + Thanks to Ralph Dolmans for finding this, and co-ordinating |
| + the vulnerability tracking and fix release. |
| + CVE-2017-15107 applies. |
| + |
| + |
| version 2.78 |
| Fix logic of appending ".<layer>" to PXE basename. Thanks to Chris |
| Novakovic for the patch. |
| diff --git a/src/dnssec.c b/src/dnssec.c |
| index a74d01ab..1417be56 100644 |
| --- a/src/dnssec.c |
| +++ b/src/dnssec.c |
| @@ -424,15 +424,17 @@ static void from_wire(char *name) |
| static int count_labels(char *name) |
| { |
| int i; |
| - |
| + char *p; |
| + |
| if (*name == 0) |
| return 0; |
| |
| - for (i = 0; *name; name++) |
| - if (*name == '.') |
| + for (p = name, i = 0; *p; p++) |
| + if (*p == '.') |
| i++; |
| |
| - return i+1; |
| + /* Don't count empty first label. */ |
| + return *name == '.' ? i : i+1; |
| } |
| |
| /* Implement RFC1982 wrapped compare for 32-bit numbers */ |
| @@ -1405,8 +1407,8 @@ static int hostname_cmp(const char *a, const char *b) |
| } |
| } |
| |
| -static int prove_non_existence_nsec(struct dns_header *header, size_t plen, unsigned char **nsecs, int nsec_count, |
| - char *workspace1, char *workspace2, char *name, int type, int *nons) |
| +static int prove_non_existence_nsec(struct dns_header *header, size_t plen, unsigned char **nsecs, unsigned char **labels, int nsec_count, |
| + char *workspace1_in, char *workspace2, char *name, int type, int *nons) |
| { |
| int i, rc, rdlen; |
| unsigned char *p, *psave; |
| @@ -1419,6 +1421,9 @@ static int prove_non_existence_nsec(struct dns_header *header, size_t plen, unsi |
| /* Find NSEC record that proves name doesn't exist */ |
| for (i = 0; i < nsec_count; i++) |
| { |
| + char *workspace1 = workspace1_in; |
| + int sig_labels, name_labels; |
| + |
| p = nsecs[i]; |
| if (!extract_name(header, plen, &p, workspace1, 1, 10)) |
| return 0; |
| @@ -1427,7 +1432,27 @@ static int prove_non_existence_nsec(struct dns_header *header, size_t plen, unsi |
| psave = p; |
| if (!extract_name(header, plen, &p, workspace2, 1, 10)) |
| return 0; |
| - |
| + |
| + /* If NSEC comes from wildcard expansion, use original wildcard |
| + as name for computation. */ |
| + sig_labels = *labels[i]; |
| + name_labels = count_labels(workspace1); |
| + |
| + if (sig_labels < name_labels) |
| + { |
| + int k; |
| + for (k = name_labels - sig_labels; k != 0; k--) |
| + { |
| + while (*workspace1 != '.' && *workspace1 != 0) |
| + workspace1++; |
| + if (k != 1 && *workspace1 == '.') |
| + workspace1++; |
| + } |
| + |
| + workspace1--; |
| + *workspace1 = '*'; |
| + } |
| + |
| rc = hostname_cmp(workspace1, name); |
| |
| if (rc == 0) |
| @@ -1825,24 +1850,26 @@ static int prove_non_existence_nsec3(struct dns_header *header, size_t plen, uns |
| |
| static int prove_non_existence(struct dns_header *header, size_t plen, char *keyname, char *name, int qtype, int qclass, char *wildname, int *nons) |
| { |
| - static unsigned char **nsecset = NULL; |
| - static int nsecset_sz = 0; |
| + static unsigned char **nsecset = NULL, **rrsig_labels = NULL; |
| + static int nsecset_sz = 0, rrsig_labels_sz = 0; |
| |
| int type_found = 0; |
| - unsigned char *p = skip_questions(header, plen); |
| + unsigned char *auth_start, *p = skip_questions(header, plen); |
| int type, class, rdlen, i, nsecs_found; |
| |
| /* Move to NS section */ |
| if (!p || !(p = skip_section(p, ntohs(header->ancount), header, plen))) |
| return 0; |
| + |
| + auth_start = p; |
| |
| for (nsecs_found = 0, i = ntohs(header->nscount); i != 0; i--) |
| { |
| unsigned char *pstart = p; |
| |
| - if (!(p = skip_name(p, header, plen, 10))) |
| + if (!extract_name(header, plen, &p, daemon->workspacename, 1, 10)) |
| return 0; |
| - |
| + |
| GETSHORT(type, p); |
| GETSHORT(class, p); |
| p += 4; /* TTL */ |
| @@ -1859,7 +1886,69 @@ static int prove_non_existence(struct dns_header *header, size_t plen, char *key |
| if (!expand_workspace(&nsecset, &nsecset_sz, nsecs_found)) |
| return 0; |
| |
| - nsecset[nsecs_found++] = pstart; |
| + if (type == T_NSEC) |
| + { |
| + /* If we're looking for NSECs, find the corresponding SIGs, to |
| + extract the labels value, which we need in case the NSECs |
| + are the result of wildcard expansion. |
| + Note that the NSEC may not have been validated yet |
| + so if there are multiple SIGs, make sure the label value |
| + is the same in all, to avoid be duped by a rogue one. |
| + If there are no SIGs, that's an error */ |
| + unsigned char *p1 = auth_start; |
| + int res, j, rdlen1, type1, class1; |
| + |
| + if (!expand_workspace(&rrsig_labels, &rrsig_labels_sz, nsecs_found)) |
| + return 0; |
| + |
| + rrsig_labels[nsecs_found] = NULL; |
| + |
| + for (j = ntohs(header->nscount); j != 0; j--) |
| + { |
| + if (!(res = extract_name(header, plen, &p1, daemon->workspacename, 0, 10))) |
| + return 0; |
| + |
| + GETSHORT(type1, p1); |
| + GETSHORT(class1, p1); |
| + p1 += 4; /* TTL */ |
| + GETSHORT(rdlen1, p1); |
| + |
| + if (!CHECK_LEN(header, p1, plen, rdlen1)) |
| + return 0; |
| + |
| + if (res == 1 && class1 == qclass && type1 == T_RRSIG) |
| + { |
| + int type_covered; |
| + unsigned char *psav = p1; |
| + |
| + if (rdlen < 18) |
| + return 0; /* bad packet */ |
| + |
| + GETSHORT(type_covered, p1); |
| + |
| + if (type_covered == T_NSEC) |
| + { |
| + p1++; /* algo */ |
| + |
| + /* labels field must be the same in every SIG we find. */ |
| + if (!rrsig_labels[nsecs_found]) |
| + rrsig_labels[nsecs_found] = p1; |
| + else if (*rrsig_labels[nsecs_found] != *p1) /* algo */ |
| + return 0; |
| + } |
| + p1 = psav; |
| + } |
| + |
| + if (!ADD_RDLEN(header, p1, plen, rdlen1)) |
| + return 0; |
| + } |
| + |
| + /* Must have found at least one sig. */ |
| + if (!rrsig_labels[nsecs_found]) |
| + return 0; |
| + } |
| + |
| + nsecset[nsecs_found++] = pstart; |
| } |
| |
| if (!ADD_RDLEN(header, p, plen, rdlen)) |
| @@ -1867,7 +1956,7 @@ static int prove_non_existence(struct dns_header *header, size_t plen, char *key |
| } |
| |
| if (type_found == T_NSEC) |
| - return prove_non_existence_nsec(header, plen, nsecset, nsecs_found, daemon->workspacename, keyname, name, qtype, nons); |
| + return prove_non_existence_nsec(header, plen, nsecset, rrsig_labels, nsecs_found, daemon->workspacename, keyname, name, qtype, nons); |
| else if (type_found == T_NSEC3) |
| return prove_non_existence_nsec3(header, plen, nsecset, nsecs_found, daemon->workspacename, keyname, name, qtype, wildname, nons); |
| else |
| -- |
| 2.19.0 |
| |