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From 159042c71bbdd5909f792208dcdffffb1674ecfe Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Petr=20P=C3=ADsa=C5=99?= <ppisar@redhat.com>
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Date: Thu, 19 Aug 2021 16:07:06 +0200
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Subject: [PATCH] Fix a crash in gss_release_oid() when destructing out_mech
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returned by gss_accept_sec_context()
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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If Perl GSSAPI was built against MIT krb5, an example gss-server.pl
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script crashed like this:
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Program terminated with signal SIGSEGV, Segmentation fault.
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#0 0x00007f27f3d48b23 in __GI___libc_free (mem=<optimized out>)
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at malloc.c:3131
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3131 ar_ptr = arena_for_chunk (p);
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(gdb) bt
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#0 0x00007f27f3d48b23 in __GI___libc_free (mem=<optimized out>)
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at malloc.c:3131
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#1 0x00007f27f2fe17c6 in generic_gss_release_oid (
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minor_status=minor_status@entry=0x7fffc750333c,
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oid=oid@entry=0x7fffc7503340) at oid_ops.c:102
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#2 0x00007f27f2fee6df in gss_release_oid (
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minor_status=minor_status@entry=0x7fffc750333c,
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oid=oid@entry=0x7fffc7503340) at g_initialize.c:202
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#3 0x00007f27f322f5cf in XS_GSSAPI__OID_DESTROY (my_perl=<optimized out>,
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cv=0x564037c87130) at ./xs/OID.xs:24
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#4 0x00007f27f4f58149 in Perl_pp_entersub (my_perl=0x5640378d42a0)
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at pp_hot.c:4227
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The cause is that gss_accept_sec_context() returns a pointer to
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a static storage in out_mech argument. When GSSAPI passed out_mech to
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a desctructor, the invoked gss_release_oid() crashed when freeing the
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memory.
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Accoding to RFC 2744, the static storage is correct. Hence the flaw is
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on Perl GSSAPI side. This patch fixes it by copying the out_mech OID
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object on a heap which is then correctly processed by
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gss_release_oid().
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CPAN RT#121873.
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Signed-off-by: Petr Písař <ppisar@redhat.com>
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---
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xs/Context.xs | 18 ++++++++++++++++++
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1 file changed, 18 insertions(+)
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diff --git a/xs/Context.xs b/xs/Context.xs
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index d176f08..4549595 100644
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--- a/xs/Context.xs
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+++ b/xs/Context.xs
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@@ -80,6 +80,24 @@ accept(context, acc_cred, in_token, binding, out_name, out_mech, out_token, out_
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&in_token, binding, out_name, out_mech,
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&out_token, out_flags, out_time,
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delegated_cred);
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+#if !defined(HEIMDAL)
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+ if (out_mech && *out_mech) {
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+ /* RFC 2744 documents that the returned *out_mech is a pointer
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+ * to static data. To prevent from freeing them when destructing
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+ * out_mech, we change *out_mech into a pointer to a heap-allocated
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+ * buffer with the same content. Otherwise, MITKRB5-provided
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+ * gss_release_oid() deallocator which cannot recognize this static
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+ * storage would crash. We use malloc() because gss_release_oid() used
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+ * free(). */
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+ GSSAPI__OID copy = malloc(sizeof(*copy));
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+ if (!copy) croak("Not enough memory for copying out_mech!");
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+ copy->elements = malloc((*out_mech)->length);
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+ if (!copy->elements) croak("Not enough memory for copying out_mech!");
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+ memcpy(copy->elements, (*out_mech)->elements, (*out_mech)->length);
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+ copy->length = (*out_mech)->length;
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+ *out_mech = copy;
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+ }
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+#endif
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OUTPUT:
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RETVAL
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context
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--
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2.31.1
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