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Merge pull request #31480 from rpigott/dnssec-maxwork

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resolved: limit the number of signature validations in a transaction
This commit is contained in:
Luca Boccassi
2024-02-26 12:26:36 +00:00
committed by GitHub
parent 7036d472d0 eba291124b
commit 26d85d9ee7
3 changed files with 41 additions and 8 deletions
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src/resolve/resolved-dns-dnssec.c
+17 -4
View File
@@ -28,8 +28,9 @@ DEFINE_TRIVIAL_CLEANUP_FUNC_FULL(EC_KEY*, EC_KEY_free, NULL);
/* Permit a maximum clock skew of 1h 10min. This should be enough to deal with DST confusion */
#define SKEW_MAX (1*USEC_PER_HOUR + 10*USEC_PER_MINUTE)
/* Maximum number of NSEC3 iterations we'll do. RFC5155 says 2500 shall be the maximum useful value */
#define NSEC3_ITERATIONS_MAX 2500
/* Maximum number of NSEC3 iterations we'll do. RFC5155 says 2500 shall be the maximum useful value, but
* RFC9276 § 3.2 says that we should reduce the acceptable iteration count */
#define NSEC3_ITERATIONS_MAX 100
/*
* The DNSSEC Chain of trust:
@@ -1169,6 +1170,7 @@ int dnssec_verify_rrset_search(
DnsResourceRecord **ret_rrsig) {
bool found_rrsig = false, found_invalid = false, found_expired_rrsig = false, found_unsupported_algorithm = false;
unsigned nvalidations = 0;
DnsResourceRecord *rrsig;
int r;
@@ -1214,6 +1216,14 @@ int dnssec_verify_rrset_search(
if (realtime == USEC_INFINITY)
realtime = now(CLOCK_REALTIME);
/* Have we seen an unreasonable number of invalid signaures? */
if (nvalidations > DNSSEC_INVALID_MAX) {
if (ret_rrsig)
*ret_rrsig = NULL;
*result = DNSSEC_TOO_MANY_VALIDATIONS;
return (int) nvalidations;
}
/* Yay, we found a matching RRSIG with a matching
* DNSKEY, awesome. Now let's verify all entries of
* the RRSet against the RRSIG and DNSKEY
@@ -1223,6 +1233,8 @@ int dnssec_verify_rrset_search(
if (r < 0)
return r;
nvalidations++;
switch (one_result) {
case DNSSEC_VALIDATED:
@@ -1233,7 +1245,7 @@ int dnssec_verify_rrset_search(
*ret_rrsig = rrsig;
*result = one_result;
return 0;
return (int) nvalidations;
case DNSSEC_INVALID:
/* If the signature is invalid, let's try another
@@ -1280,7 +1292,7 @@ int dnssec_verify_rrset_search(
if (ret_rrsig)
*ret_rrsig = NULL;
return 0;
return (int) nvalidations;
}
int dnssec_has_rrsig(DnsAnswer *a, const DnsResourceKey *key) {
@@ -2565,6 +2577,7 @@ static const char* const dnssec_result_table[_DNSSEC_RESULT_MAX] = {
[DNSSEC_NSEC_MISMATCH] = "nsec-mismatch",
[DNSSEC_INCOMPATIBLE_SERVER] = "incompatible-server",
[DNSSEC_UPSTREAM_FAILURE] = "upstream-failure",
[DNSSEC_TOO_MANY_VALIDATIONS] = "too-many-validations",
};
DEFINE_STRING_TABLE_LOOKUP(dnssec_result, DnssecResult);
src/resolve/resolved-dns-dnssec.h
+8 -1
View File
@@ -9,12 +9,13 @@ typedef enum DnssecVerdict DnssecVerdict;
#include "resolved-dns-rr.h"
enum DnssecResult {
/* These five are returned by dnssec_verify_rrset() */
/* These six are returned by dnssec_verify_rrset() */
DNSSEC_VALIDATED,
DNSSEC_VALIDATED_WILDCARD, /* Validated via a wildcard RRSIG, further NSEC/NSEC3 checks necessary */
DNSSEC_INVALID,
DNSSEC_SIGNATURE_EXPIRED,
DNSSEC_UNSUPPORTED_ALGORITHM,
DNSSEC_TOO_MANY_VALIDATIONS,
/* These two are added by dnssec_verify_rrset_search() */
DNSSEC_NO_SIGNATURE,
@@ -46,6 +47,12 @@ enum DnssecVerdict {
/* The longest digest we'll ever generate, of all digest algorithms we support */
#define DNSSEC_HASH_SIZE_MAX (MAX(20, 32))
/* The most invalid signatures we will tolerate for a single rrset */
#define DNSSEC_INVALID_MAX 5
/* The total number of signature validations we will tolerate for a single transaction */
#define DNSSEC_VALIDATION_MAX 64
int dnssec_rrsig_match_dnskey(DnsResourceRecord *rrsig, DnsResourceRecord *dnskey, bool revoked_ok);
int dnssec_key_match_rrsig(const DnsResourceKey *key, DnsResourceRecord *rrsig);
src/resolve/resolved-dns-transaction.c
+16 -3
View File
@@ -3232,11 +3232,14 @@ static int dnssec_validate_records(
DnsTransaction *t,
Phase phase,
bool *have_nsec,
unsigned *nvalidations,
DnsAnswer **validated) {
DnsResourceRecord *rr;
int r;
assert(nvalidations);
/* Returns negative on error, 0 if validation failed, 1 to restart validation, 2 when finished. */
DNS_ANSWER_FOREACH(rr, t->answer) {
@@ -3278,6 +3281,7 @@ static int dnssec_validate_records(
&rrsig);
if (r < 0)
return r;
*nvalidations += r;
log_debug("Looking at %s: %s", strna(dns_resource_record_to_string(rr)), dnssec_result_to_string(result));
@@ -3475,7 +3479,8 @@ static int dnssec_validate_records(
DNSSEC_SIGNATURE_EXPIRED,
DNSSEC_NO_SIGNATURE))
manager_dnssec_verdict(t->scope->manager, DNSSEC_BOGUS, rr->key);
else /* DNSSEC_MISSING_KEY or DNSSEC_UNSUPPORTED_ALGORITHM */
else /* DNSSEC_MISSING_KEY, DNSSEC_UNSUPPORTED_ALGORITHM,
or DNSSEC_TOO_MANY_VALIDATIONS */
manager_dnssec_verdict(t->scope->manager, DNSSEC_INDETERMINATE, rr->key);
/* This is a primary response to our question, and it failed validation.
@@ -3568,13 +3573,21 @@ int dns_transaction_validate_dnssec(DnsTransaction *t) {
return r;
phase = DNSSEC_PHASE_DNSKEY;
for (;;) {
for (unsigned nvalidations = 0;;) {
bool have_nsec = false;
r = dnssec_validate_records(t, phase, &have_nsec, &validated);
r = dnssec_validate_records(t, phase, &have_nsec, &nvalidations, &validated);
if (r <= 0)
return r;
if (nvalidations > DNSSEC_VALIDATION_MAX) {
/* This reply requires an onerous number of signature validations to verify. Let's
* not waste our time trying, as this shouldn't happen for well-behaved domains
* anyway. */
t->answer_dnssec_result = DNSSEC_TOO_MANY_VALIDATIONS;
return 0;
}
/* Try again as long as we managed to achieve something */
if (r == 1)
continue;