This PR is also sent to the OpenSSL developers via their Request Tracker
system as it is not FreeBSD related. It can be located at:
http://marc.theaimsgroup.com/?l=openssl-dev&m=111383480516715&w=2
http://www.aet.TU-Cottbus.DE/rt2/Ticket/Display.html?id=1047

There is a bug in sk_insert() function which (sometimes) causes segfaults.

sk_insert() breaks consistency of the stack in which it inserts elements
by not NULL-terminating it when element is inserted on the last position
(over the last (NULL) element). This then causes bogus pointers
dereferencing and signal 11 to be received by the program.

for example imagine the following stack:
st->num = 3
A B C NULL bogus bogus ...
after insering element D at position 4 stack looks like this:
st->num = 4
A B C D bogus bogus ...
but should be like this:
st->num = 4
A B C D NULL bogus ...

The reason crashes do not occur every time is that memory returned by
OPENSSL_realloc in most cases is initialized with zeroes (bogus==NULL
in the above example).

---- output from openssl's make report {
OpenSSL self-test report:

OpenSSL version:  0.9.7d
Last change:      Fix null-pointer assignment in do_change_cipher_spec() ...
Options:           no-krb5
OS (uname):       FreeBSD f4.bg.datamax 4.11-STABLE FreeBSD 4.11-STABLE #0: Tue Apr 12 13:06:12 GMT 2005     root@f4.bg.datamax:/usr/obj/usr/src/sys/F4  i386
OS (config):      i386-pc-freebsd4.11
Target (default): FreeBSD-elf
Target:           dist
Compiler:         Using builtin specs.
gcc version 2.95.4 20020320 [FreeBSD]

Test passed.
---- } output from openssl's make report

As I see this would also be a problem in the latest version 0.9.7g.

---- backtrace {
Core was generated by `php'.
Program terminated with signal 11, Segmentation fault.
#0  0x283cf537 in engine_table_select (table=0x2840cc80, nid=1)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/engine/eng_table.c:306
306		if((ret->funct_ref > 0) || !(table_flags & ENGINE_TABLE_FLAG_NOINIT))
#0  0x283cf537 in engine_table_select (table=0x2840cc80, nid=1)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/engine/eng_table.c:306
#1  0x2839c7de in ENGINE_get_default_RSA ()
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/engine/tb_rsa.c:106
#2  0x2839a165 in RSA_new_method (engine=0x0)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/rsa/rsa_lib.c:156
#3  0x28399f58 in RSA_new ()
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/rsa/rsa_lib.c:77
#4  0x283c0c71 in rsa_cb (operation=0, pval=0xbfbfdcf4, it=0x28414874)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/rsa/rsa_asn1.c:80
#5  0x283d227c in asn1_item_ex_combine_new (pval=0xbfbfdcf4, it=0x28414874, combine=0)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/asn1/tasn_new.c:160
#6  0x283d1fe4 in ASN1_item_ex_new (pval=0xbfbfdcf4, it=0x28414874)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/asn1/tasn_new.c:83
#7  0x283cc488 in ASN1_item_ex_d2i (pval=0xbfbfdcf4, in=0xbfbfdda0, len=137, it=0x28414874, 
    tag=16, aclass=0, opt=0 '\000', ctx=0xbfbfdcf8)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/asn1/tasn_dec.c:317
#8  0x283cbd54 in ASN1_item_d2i (pval=0xbfbfdcf4, in=0xbfbfdda0, len=140, it=0x28414874)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/asn1/tasn_dec.c:115
#9  0x283c0d7c in d2i_RSAPublicKey (a=0x0, in=0xbfbfdda0, len=140)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/rsa/rsa_asn1.c:111
#10 0x283b62b2 in d2i_PublicKey (type=6, a=0x0, pp=0xbfbfdda0, length=140)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/asn1/d2i_pu.c:93
#11 0x283b465a in X509_PUBKEY_get (key=0x81c89d0)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/asn1/x_pubkey.c:194
#12 0x283b2fe5 in X509_get_pubkey (x=0x81c2a80)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/x509/x509_cmp.c:362
#13 0x283311f2 in X509_get_pubkey_parameters (pkey=0x0, chain=0x81c6d20)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/x509/x509_vfy.c:902
#14 0x2832fe71 in X509_verify_cert (ctx=0xbfbfdea4)
    at /usr/src/secure/lib/libcrypto/../../../crypto/openssl/crypto/x509/x509_vfy.c:295
#15 0x282c2ecc in ssl_verify_cert_chain (s=0x81c7e00, sk=0x81c6700)
    at /usr/src/secure/lib/libssl/../../../crypto/openssl/ssl/ssl_cert.c:494
#16 0x282a8b4c in ssl3_get_server_certificate (s=0x81c7e00)
    at /usr/src/secure/lib/libssl/../../../crypto/openssl/ssl/s3_clnt.c:833
#17 0x282a78e1 in ssl3_connect (s=0x81c7e00)
    at /usr/src/secure/lib/libssl/../../../crypto/openssl/ssl/s3_clnt.c:275
#18 0x282bad4d in SSL_connect (s=0x81c7e00)
    at /usr/src/secure/lib/libssl/../../../crypto/openssl/ssl/ssl_lib.c:824
#19 0x282a5e99 in ssl23_get_server_hello (s=0x81c7e00)
    at /usr/src/secure/lib/libssl/../../../crypto/openssl/ssl/s23_clnt.c:486
#20 0x282a54cc in ssl23_connect (s=0x81c7e00)
    at /usr/src/secure/lib/libssl/../../../crypto/openssl/ssl/s23_clnt.c:187
#21 0x282bad4d in SSL_connect (s=0x81c7e00)
    at /usr/src/secure/lib/libssl/../../../crypto/openssl/ssl/ssl_lib.c:824
#22 0x2827eb4c in Curl_SSLConnect (conn=0x817d000, sockindex=0) at ssluse.c:1504
#23 0x2826b8a3 in Curl_http_connect (conn=0x817d000, done=0xbfbfe2b6 "") at http.c:1262
#24 0x282784be in Curl_protocol_connect (conn=0x817d000, protocol_done=0xbfbfe2b6 "") at url.c:2099
#25 0x2827ab51 in SetupConnection (conn=0x817d000, hostaddr=0x81794a0, protocol_done=0xbfbfe2b6 "")
    at url.c:3513
#26 0x2827ac4e in Curl_connect (data=0x818c000, in_connect=0xbfbfe2f4, asyncp=0xbfbfe2b7 "", 
    protocol_done=0xbfbfe2b6 "") at url.c:3569
#27 0x28287ec0 in Curl_connect_host (data=0x818c000, conn=0xbfbfe2f4) at transfer.c:2054
#28 0x2828810c in Curl_perform (data=0x818c000) at transfer.c:2142
#29 0x28288ab8 in curl_easy_perform (curl=0x818c000) at easy.c:474
#30 0x2825956d in zif_curl_exec (ht=1, return_value=0x81843ec, this_ptr=0x0, return_value_used=0)
    at /usr/ports/ftp/php4-curl/work/php-4.3.11/ext/curl/curl.c:1127
#31 0x8102425 in execute (op_array=0x818340c)
    at /usr/ports/lang/php4-cli/work/php-4.3.11/Zend/zend_execute.c:1654
#32 0x80f0bad in zend_execute_scripts (type=8, retval=0x0, file_count=3)
    at /usr/ports/lang/php4-cli/work/php-4.3.11/Zend/zend.c:926
#33 0x80c0753 in php_execute_script (primary_file=0xbfbffb54)
    at /usr/ports/lang/php4-cli/work/php-4.3.11/main/main.c:1745
#34 0x8108087 in main (argc=2, argv=0xbfbffbd0)
    at /usr/ports/lang/php4-cli/work/php-4.3.11/sapi/cli/php_cli.c:828
---- } backtrace

(gdb) ins *ret
Cannot access memory at address 0x726f7020.
(gdb)

The "goto trynext;" loop walks on the stack waiting for NULL element to
indicate "stack end" but hits a invalid pointer instead and crashes while
trying to dereference it.

Fix: ---- stack.c.patch {
How-To-Repeat: 
Huh, really complicated, probably there is an easier way.

On a FreeBSD4.11 i386 machine do the following:

$ cd /usr/ports/lang/php4 && make install
$ cd /usr/ports/ftp/php4-curl && make install
$ cd /usr/ports/databases/php4-mysql && make install
$ cd /usr/ports/security/php4-openssl && make install

then make sure /usr/local/etc/php/extensions.ini contains
extension=curl.so
extension=mysql.so
extension=openssl.so
exactly in that order. Other orders do not produce the crash -
OPENSSL_realloc() returns 0x0-initialized memory.

create foo.php that contains:
<?php
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'https://www.thawte.com/');
curl_exec($ch);
curl_close($ch);
?>

and then execute it:
$ php foo.php
Segmentation fault (core dumped)
$

Notice that even changing the order of shared objects in extensions.ini
does not produce a crash so this will (probably) be very difficult to
reproduce on a machine with different setup.

I suggest altering malloc/realloc functions to initialize returned memory
with non-zeros - than the bug will be easier to reproduce.

Thanks to Toni Viemero for finding and reporting this problem to the
FreeBSD GNATS system:

http://www.FreeBSD.org/cgi/query-pr.cgi?pr=79617