| From 4fe6744a220eddd3f1749b40cac3dfc510787de6 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. |
| |
| [baruch: drop the CHANGELOG hunk] |
| Signed-off-by: Baruch Siach <baruch@tkos.co.il> |
| --- |
| Upstream status: upstream commit 4fe6744a220e |
| |
| CHANGELOG | 12 +++++- |
| src/dnssec.c | 117 ++++++++++++++++++++++++++++++++++++++++++++++++++++------- |
| 2 files changed, 114 insertions(+), 15 deletions(-) |
| |
| diff --git a/src/dnssec.c b/src/dnssec.c |
| index eb6c11cbe00f..a54a0b4f14cf 100644 |
| --- a/src/dnssec.c |
| +++ b/src/dnssec.c |
| @@ -103,15 +103,17 @@ 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 */ |
| @@ -1094,8 +1096,8 @@ 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; |
| @@ -1108,6 +1110,9 @@ 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; |
| @@ -1116,7 +1121,27 @@ 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) |
| @@ -1514,24 +1539,26 @@ 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 */ |
| @@ -1548,7 +1575,69 @@ 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)) |
| @@ -1556,7 +1645,7 @@ 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 |
| -- |
| 2.15.1 |
| |