sm: Another partly rewrite of minip12.c

* sm/minip12.c (struct tlv_ctx_s): Add origbuffer and origbufsize.
Remove pop_count.  Rename offset to length.
(dump_tag_info, _dump_tag_info): Rewrite.
(dump_tlv_ctx, _dump_tlv_ctx): Rewrite.
(tlv_new): Init origbuffer.
(_tlv_peek): Add arg ti.
(tlv_peek): New.
(tlv_peek_null): New.
(_tlv_push): Rewrite.
(_tlv_pop): Rewrite.
(tlv_next): New macro.  Move old code to ...
(_tlv_next): this.  Add arg lno.  Pop remaining end tags.
(tlv_popped): Remove.
(tlv_expect_object): Handle ndef.
(tlv_expect_octet_string): Ditto.
(parse_bag_encrypted_data): Use nesting level to control the inner
loop.
(parse_shrouded_key_bag): Likewise.
(parse_bag_data): Handle surplus octet strings.
(p12_parse): Ditto.

* sm/minip12.c (decrypt_block): Strip the padding.
(tlv_expect_top_sequence): Remove.  Replace callers by
tlv_expect_sequence.

* tests/cms/samplekeys/t6752-ov-user-ff.p12: New sample key.
* tests/cms/samplekeys/Description-p12: Add its description
--

This patch improves the BER parser by simplifying it.  Now tlv_next
pops off and thus closes all containers regardless on whether they are
length bounded or ndef.  tlv_set_pending is now always used to undo
the effect of a tlv_next in a loop condition which was terminated by a
nesting level change.

Instead of using the length as seen in the decrypted container we now
remove the padding and let the BER parser do its work.  This might
have a negative effect on pkcs#12 objects which are not correctly
padded but we don't have any example of such broken objects.

GnuPG-bug-id: 6752

tests/cms/samplekeys/Description-p12

@@ -45,4 +45,10 @@ Pass: abc
 Cert: 5cea0c5bf09ccd92535267c662fc098f6c81c27e
 Key:  3cb2fba95d1976df69eb7aa8c65ac5354e15af32
 
+Name: t6752-ov-user-ff.p12
+Desc: Mozilla generated with a surplus octet string container
+Pass: start
+Cert: 4753a910e0c8b4caa8663ca0e4273a884eb5397d
+Key:  93be89edd11214ab74280d988a665b6beef876c5
+
 # eof #