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@@ -0,0 +1,173 @@
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+Upstream-Status: Backport
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+Signed-off-by: Ross Burton <ross.burton@intel.com>
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+
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+From d59e31fc729d8a39a774f03bc6bc457029a7aef2 Mon Sep 17 00:00:00 2001
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+From: Yves Orton <demerphq@gmail.com>
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+Date: Tue, 12 Feb 2013 10:53:05 +0100
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+Subject: [PATCH] Prevent premature hsplit() calls, and only trigger REHASH after hsplit()
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+
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+Triggering a hsplit due to long chain length allows an attacker
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+to create a carefully chosen set of keys which can cause the hash
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+to use 2 * (2**32) * sizeof(void *) bytes ram. AKA a DOS via memory
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+exhaustion. Doing so also takes non trivial time.
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+
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+Eliminating this check, and only inspecting chain length after a
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+normal hsplit() (triggered when keys>buckets) prevents the attack
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+entirely, and makes such attacks relatively benign.
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+
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+(cherry picked from commit f1220d61455253b170e81427c9d0357831ca0fac)
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+---
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+ ext/Hash-Util-FieldHash/t/10_hash.t | 18 ++++++++++++++++--
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+ hv.c | 35 ++++++++---------------------------
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+ t/op/hash.t | 20 +++++++++++++++++---
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+ 3 files changed, 41 insertions(+), 32 deletions(-)
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+
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+diff --git a/ext/Hash-Util-FieldHash/t/10_hash.t b/ext/Hash-Util-FieldHash/t/10_hash.t
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+index 2cfb4e8..d58f053 100644
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+--- a/ext/Hash-Util-FieldHash/t/10_hash.t
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++++ b/ext/Hash-Util-FieldHash/t/10_hash.t
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+@@ -38,15 +38,29 @@ use constant START => "a";
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+
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+ # some initial hash data
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+ fieldhash my %h2;
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+-%h2 = map {$_ => 1} 'a'..'cc';
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++my $counter= "a";
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++$h2{$counter++}++ while $counter ne 'cd';
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+
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+ ok (!Internals::HvREHASH(%h2),
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+ "starting with pre-populated non-pathological hash (rehash flag if off)");
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+
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+ my @keys = get_keys(\%h2);
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++my $buckets= buckets(\%h2);
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+ $h2{$_}++ for @keys;
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++$h2{$counter++}++ while buckets(\%h2) == $buckets; # force a split
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+ ok (Internals::HvREHASH(%h2),
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+- scalar(@keys) . " colliding into the same bucket keys are triggering rehash");
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++ scalar(@keys) . " colliding into the same bucket keys are triggering rehash after split");
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++
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++# returns the number of buckets in a hash
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++sub buckets {
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++ my $hr = shift;
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++ my $keys_buckets= scalar(%$hr);
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++ if ($keys_buckets=~m!/([0-9]+)\z!) {
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++ return 0+$1;
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++ } else {
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++ return 8;
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++ }
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++}
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+
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+ sub get_keys {
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+ my $hr = shift;
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+diff --git a/hv.c b/hv.c
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+index 2be1feb..abb9d76 100644
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+--- a/hv.c
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++++ b/hv.c
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+@@ -35,7 +35,8 @@ holds the key and hash value.
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+ #define PERL_HASH_INTERNAL_ACCESS
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+ #include "perl.h"
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+
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+-#define HV_MAX_LENGTH_BEFORE_SPLIT 14
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++#define HV_MAX_LENGTH_BEFORE_REHASH 14
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++#define SHOULD_DO_HSPLIT(xhv) ((xhv)->xhv_keys > (xhv)->xhv_max) /* HvTOTALKEYS(hv) > HvMAX(hv) */
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+
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+ static const char S_strtab_error[]
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+ = "Cannot modify shared string table in hv_%s";
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+@@ -794,29 +795,9 @@ Perl_hv_common(pTHX_ HV *hv, SV *keysv, const char *key, STRLEN klen,
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+ if (masked_flags & HVhek_ENABLEHVKFLAGS)
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+ HvHASKFLAGS_on(hv);
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+
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+- {
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+- const HE *counter = HeNEXT(entry);
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+-
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+- xhv->xhv_keys++; /* HvTOTALKEYS(hv)++ */
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+- if (!counter) { /* initial entry? */
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+- } else if (xhv->xhv_keys > xhv->xhv_max) {
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+- /* Use only the old HvKEYS(hv) > HvMAX(hv) condition to limit
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+- bucket splits on a rehashed hash, as we're not going to
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+- split it again, and if someone is lucky (evil) enough to
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+- get all the keys in one list they could exhaust our memory
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+- as we repeatedly double the number of buckets on every
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+- entry. Linear search feels a less worse thing to do. */
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+- hsplit(hv);
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+- } else if(!HvREHASH(hv)) {
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+- U32 n_links = 1;
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+-
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+- while ((counter = HeNEXT(counter)))
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+- n_links++;
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+-
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+- if (n_links > HV_MAX_LENGTH_BEFORE_SPLIT) {
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+- hsplit(hv);
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+- }
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+- }
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++ xhv->xhv_keys++; /* HvTOTALKEYS(hv)++ */
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++ if ( SHOULD_DO_HSPLIT(xhv) ) {
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++ hsplit(hv);
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+ }
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+
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+ if (return_svp) {
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+@@ -1192,7 +1173,7 @@ S_hsplit(pTHX_ HV *hv)
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+
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+
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+ /* Pick your policy for "hashing isn't working" here: */
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+- if (longest_chain <= HV_MAX_LENGTH_BEFORE_SPLIT /* split worked? */
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++ if (longest_chain <= HV_MAX_LENGTH_BEFORE_REHASH /* split worked? */
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+ || HvREHASH(hv)) {
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+ return;
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+ }
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+@@ -2831,8 +2812,8 @@ S_share_hek_flags(pTHX_ const char *str, I32 len, register U32 hash, int flags)
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+
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+ xhv->xhv_keys++; /* HvTOTALKEYS(hv)++ */
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+ if (!next) { /* initial entry? */
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+- } else if (xhv->xhv_keys > xhv->xhv_max /* HvKEYS(hv) > HvMAX(hv) */) {
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+- hsplit(PL_strtab);
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++ } else if ( SHOULD_DO_HSPLIT(xhv) ) {
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++ hsplit(PL_strtab);
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+ }
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+ }
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+
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+diff --git a/t/op/hash.t b/t/op/hash.t
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+index 278bea7..201260a 100644
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+--- a/t/op/hash.t
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++++ b/t/op/hash.t
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+@@ -39,22 +39,36 @@ use constant THRESHOLD => 14;
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+ use constant START => "a";
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+
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+ # some initial hash data
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+-my %h2 = map {$_ => 1} 'a'..'cc';
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++my %h2;
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++my $counter= "a";
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++$h2{$counter++}++ while $counter ne 'cd';
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+
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+ ok (!Internals::HvREHASH(%h2),
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+ "starting with pre-populated non-pathological hash (rehash flag if off)");
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+
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+ my @keys = get_keys(\%h2);
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++my $buckets= buckets(\%h2);
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+ $h2{$_}++ for @keys;
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++$h2{$counter++}++ while buckets(\%h2) == $buckets; # force a split
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+ ok (Internals::HvREHASH(%h2),
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+- scalar(@keys) . " colliding into the same bucket keys are triggering rehash");
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++ scalar(@keys) . " colliding into the same bucket keys are triggering rehash after split");
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++
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++# returns the number of buckets in a hash
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++sub buckets {
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++ my $hr = shift;
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++ my $keys_buckets= scalar(%$hr);
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++ if ($keys_buckets=~m!/([0-9]+)\z!) {
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++ return 0+$1;
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++ } else {
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++ return 8;
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++ }
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++}
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+
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+ sub get_keys {
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+ my $hr = shift;
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+
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+ # the minimum of bits required to mount the attack on a hash
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+ my $min_bits = log(THRESHOLD)/log(2);
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+-
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+ # if the hash has already been populated with a significant amount
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+ # of entries the number of mask bits can be higher
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+ my $keys = scalar keys %$hr;
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+--
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+1.7.4.1
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