Attachment 698790 Details for Bug 912276 – Proposed upstream patch against perl-5.8.8 version

[patch] Proposed upstream patch against perl-5.8.8 version

rehash-5.8.8.patch (text/plain), 4.32 KB, created by Jan Lieskovsky on 2013-02-18 09:41:13 UTC

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Creator: Jan Lieskovsky

Created: 2013-02-18 09:41:13 UTC

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patch

obsolete

>>From 2674b61957c26a4924831d5110afa454ae7ae5a6 Mon Sep 17 00:00:00 2001
>From: Yves Orton <demerphq@gmail.com>
>Date: Tue, 12 Feb 2013 10:53:05 +0100
>Subject: [PATCH] Prevent premature hsplit() calls, and only trigger REHASH
> after hsplit()
>
>Triggering a hsplit due to long chain length allows an attacker
>to create a carefully chosen set of keys which can cause the hash
>to use 2 * (2**32) * sizeof(void *) bytes ram. AKA a DOS via memory
>exhaustion. Doing so also takes non trivial time.
>
>Eliminating this check, and only inspecting chain length after a
>normal hsplit() (triggered when keys>buckets) prevents the attack
>entirely, and makes such attacks relatively benign.
>
>(cherry picked from commit f14269908e5f8b4cab4b55643d7dd9de577e7918)
>(which was itself cherry picked from commit f2a571dae7d70f7e3b59022834d8003ecd2df884)
>(which was itself cherry picked (with changes) from commit f1220d61455253b170e81427c9d0357831ca0fac)
>---
> hv.c        | 26 ++++++--------------------
> t/op/hash.t | 20 +++++++++++++++++---
> 2 files changed, 23 insertions(+), 23 deletions(-)
>
>diff --git a/hv.c b/hv.c
>index 030db74..0d15a40 100644
>--- a/hv.c
>+++ b/hv.c
>@@ -31,7 +31,8 @@ holds the key and hash value.
> #define PERL_HASH_INTERNAL_ACCESS
> #include "perl.h"
> 
>-#define HV_MAX_LENGTH_BEFORE_SPLIT 14
>+#define HV_MAX_LENGTH_BEFORE_REHASH 14
>+#define SHOULD_DO_HSPLIT(xhv) ((xhv)->xhv_keys > (xhv)->xhv_max) /* HvTOTALKEYS(hv) > HvMAX(hv) */
> 
> STATIC void
> S_more_he(pTHX)
>@@ -705,23 +706,8 @@ Perl_hv_common(pTHX_ HV *hv, SV *keysv, const char *key, STRLEN klen,
> 	xhv->xhv_keys++; /* HvTOTALKEYS(hv)++ */
> 	if (!counter) {				/* initial entry? */
> 	    xhv->xhv_fill++; /* HvFILL(hv)++ */
>-	} else if (xhv->xhv_keys > (IV)xhv->xhv_max) {
>+	} else if ( SHOULD_DO_HSPLIT(xhv) ) {
> 	    hsplit(hv);
>-	} else if(!HvREHASH(hv)) {
>-	    U32 n_links = 1;
>-
>-	    while ((counter = HeNEXT(counter)))
>-		n_links++;
>-
>-	    if (n_links > HV_MAX_LENGTH_BEFORE_SPLIT) {
>-		/* Use only the old HvKEYS(hv) > HvMAX(hv) condition to limit
>-		   bucket splits on a rehashed hash, as we're not going to
>-		   split it again, and if someone is lucky (evil) enough to
>-		   get all the keys in one list they could exhaust our memory
>-		   as we repeatedly double the number of buckets on every
>-		   entry. Linear search feels a less worse thing to do.  */
>-		hsplit(hv);
>-	    }
> 	}
>     }
> 
>@@ -1048,7 +1034,7 @@ S_hsplit(pTHX_ HV *hv)
> 
> 
>     /* Pick your policy for "hashing isn't working" here:  */
>-    if (longest_chain <= HV_MAX_LENGTH_BEFORE_SPLIT /* split worked?  */
>+    if (longest_chain <= HV_MAX_LENGTH_BEFORE_REHASH /* split worked?  */
> 	|| HvREHASH(hv)) {
> 	return;
>     }
>@@ -1966,8 +1952,8 @@ S_share_hek_flags(pTHX_ const char *str, I32 len, register U32 hash, int flags)
> 	xhv->xhv_keys++; /* HvTOTALKEYS(hv)++ */
> 	if (!next) {			/* initial entry? */
> 	    xhv->xhv_fill++; /* HvFILL(hv)++ */
>-	} else if (xhv->xhv_keys > (IV)xhv->xhv_max /* HvKEYS(hv) > HvMAX(hv) */) {
>-		hsplit(PL_strtab);
>+	} else if ( SHOULD_DO_HSPLIT(xhv) ) {
>+            hsplit(PL_strtab);
> 	}
>     }
> 
>diff --git a/t/op/hash.t b/t/op/hash.t
>index 9bde518..45eb782 100644
>--- a/t/op/hash.t
>+++ b/t/op/hash.t
>@@ -39,22 +39,36 @@ use constant THRESHOLD => 14;
> use constant START     => "a";
> 
> # some initial hash data
>-my %h2 = map {$_ => 1} 'a'..'cc';
>+my %h2;
>+my $counter= "a";
>+$h2{$counter++}++ while $counter ne 'cd';
> 
> ok (!Internals::HvREHASH(%h2), 
>     "starting with pre-populated non-pathological hash (rehash flag if off)");
> 
> my @keys = get_keys(\%h2);
>+my $buckets= buckets(\%h2);
> $h2{$_}++ for @keys;
>+$h2{$counter++}++ while buckets(\%h2) == $buckets; # force a split
> ok (Internals::HvREHASH(%h2), 
>-    scalar(@keys) . " colliding into the same bucket keys are triggering rehash");
>+    scalar(@keys) . " colliding into the same bucket keys are triggering rehash after split");
>+
>+# returns the number of buckets in a hash
>+sub buckets {
>+    my $hr = shift;
>+    my $keys_buckets= scalar(%$hr);
>+    if ($keys_buckets=~m!/([0-9]+)\z!) {
>+        return 0+$1;
>+    } else {
>+        return 8;
>+    }
>+}
> 
> sub get_keys {
>     my $hr = shift;
> 
>     # the minimum of bits required to mount the attack on a hash
>     my $min_bits = log(THRESHOLD)/log(2);
>-
>     # if the hash has already been populated with a significant amount
>     # of entries the number of mask bits can be higher
>     my $keys = scalar keys %$hr;
>-- 
>1.8.1.3
>

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