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0001-gpg-Fix-newlines-in-Cleartext-Signature-Framework-CS.patch
dkg (Daniel Kahn Gillmor)
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Fri, Feb 21, 7:33 PM
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0001-gpg-Fix-newlines-in-Cleartext-Signature-Framework-CS.patch
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From 291b8078a2903ea388cd6c8fdbaeff2792ad416c Mon Sep 17 00:00:00 2001
From: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Date: Thu, 20 Feb 2025 20:03:48 -0500
Subject: [PATCH GnuPG] gpg: Fix newlines in Cleartext Signature Framework
(CSF) messages
* g10/armor.c (fake_packet): trim the final newline (and any trailing
whitespace) from synthetic literal data packet when parsing CSF.
* g10/plaintext.c (handle_plaintext): don't drop final newline when
verifying a CSF message.
* g10/textfilter.c (copy_clearsig_text): digest each newline in the
text to be signed, and always emit a non-digested additional newline
before the signature section.
* tests/openpgp/clearsig.scm: tighten up tests to confirm equality
even when the message has no final newline.
--
https://datatracker.ietf.org/doc/html/rfc9580#section-7.1-3
https://datatracker.ietf.org/doc/html/rfc4880#section-7.1
Says:
> The line ending (i.e., the <CR><LF>) before the '-----BEGIN PGP
> SIGNATURE-----' line that terminates the signed text is not
> considered part of the signed text.
Before this change, GnuPG would emit a spurious newline at the end of
the message when verifying a CSF message, even if the signed text did
not contain an extra newline.
This change aligns the output of gpg -- when generating and verifying
CSF messages -- to match the input exactly. When signing, it produces
a signature over the textmode version of the input material. And when
verifying while producing output, it produces output corresponding to
the signed material.
GnuPG-bug-id: 7106
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
---
g10/armor.c | 10 ++++++++++
g10/plaintext.c | 39 ++++++--------------------------------
g10/textfilter.c | 17 ++++++-----------
tests/openpgp/clearsig.scm | 15 ++++++---------
4 files changed, 28 insertions(+), 53 deletions(-)
diff --git a/g10/armor.c b/g10/armor.c
index 036b72772..7481894f8 100644
--- a/g10/armor.c
+++ b/g10/armor.c
@@ -785,6 +785,16 @@ fake_packet( armor_filter_context_t *afx, IOBUF a,
}
if( lastline ) { /* write last (ending) length header */
+ /* drop the final newline and any trailing whitespace before the BEGIN PGP SIGNATURE divider
+ * see RFC 4880 section 7.1 */
+ if (tempbuf_len && tempbuf[tempbuf_len-1] == '\n')
+ tempbuf_len -= 1;
+ if (tempbuf_len && tempbuf[tempbuf_len-1] == '\r')
+ tempbuf_len -= 1;
+ if( !afx->not_dash_escaped )
+ while (tempbuf_len && isblank(tempbuf[tempbuf_len-1]))
+ tempbuf_len -= 1;
+
if(tempbuf_len<192)
buf[len++]=tempbuf_len;
else
diff --git a/g10/plaintext.c b/g10/plaintext.c
index a96214994..ff001e971 100644
--- a/g10/plaintext.c
+++ b/g10/plaintext.c
@@ -432,9 +432,9 @@ handle_plaintext (PKT_plaintext * pt, md_filter_context_t * mfx,
}
pt->buf = NULL;
}
- else /* Clear text signature - don't hash the last CR,LF. */
+ else /* Clear text signature. */
{
- int state = 0;
+ int cr = 0;
while ((c = iobuf_get (pt->buf)) != -1)
{
@@ -457,37 +457,10 @@ handle_plaintext (PKT_plaintext * pt, md_filter_context_t * mfx,
}
if (!mfx->md)
continue;
- if (state == 2)
- {
- gcry_md_putc (mfx->md, '\r');
- gcry_md_putc (mfx->md, '\n');
- state = 0;
- }
- if (!state)
- {
- if (c == '\r')
- state = 1;
- else if (c == '\n')
- state = 2;
- else
- gcry_md_putc (mfx->md, c);
- }
- else if (state == 1)
- {
- if (c == '\n')
- state = 2;
- else
- {
- gcry_md_putc (mfx->md, '\r');
- if (c == '\r')
- state = 1;
- else
- {
- state = 0;
- gcry_md_putc (mfx->md, c);
- }
- }
- }
+ if ((c == '\n') && !cr)
+ gcry_md_putc (mfx->md, '\r');
+ gcry_md_putc (mfx->md, c);
+ cr = (c == '\r');
}
pt->buf = NULL;
}
diff --git a/g10/textfilter.c b/g10/textfilter.c
index 3e68900bb..d8837b30e 100644
--- a/g10/textfilter.c
+++ b/g10/textfilter.c
@@ -167,7 +167,6 @@ copy_clearsig_text( IOBUF out, IOBUF inp, gcry_md_hd_t md,
unsigned int bufsize = 0; /* and size of this buffer */
unsigned int n;
int truncated = 0;
- int pending_lf = 0;
if( !escape_dash )
escape_from = 0;
@@ -185,16 +184,15 @@ copy_clearsig_text( IOBUF out, IOBUF inp, gcry_md_hd_t md,
/* update the message digest */
if( escape_dash ) {
- if( pending_lf ) {
- gcry_md_putc ( md, '\r' );
- gcry_md_putc ( md, '\n' );
- }
gcry_md_write ( md, buffer,
len_without_trailing_chars (buffer, n, " \t\r\n"));
+ if (buffer[n-1] == '\n') {
+ gcry_md_putc ( md, '\r' );
+ gcry_md_putc ( md, '\n' );
+ }
}
else
gcry_md_write ( md, buffer, n );
- pending_lf = buffer[n-1] == '\n';
/* write the output */
if( ( escape_dash && *buffer == '-')
@@ -231,11 +229,8 @@ copy_clearsig_text( IOBUF out, IOBUF inp, gcry_md_hd_t md,
}
/* at eof */
- if( !pending_lf ) { /* make sure that the file ends with a LF */
- iobuf_writestr( out, LF );
- if( !escape_dash )
- gcry_md_putc( md, '\n' );
- }
+ /* add a newline before signature is emitted: */
+ iobuf_writestr( out, LF );
if( truncated )
log_info(_("input line longer than %d characters\n"), MAX_LINELEN );
diff --git a/tests/openpgp/clearsig.scm b/tests/openpgp/clearsig.scm
index b1c72c2ec..02c79d997 100755
--- a/tests/openpgp/clearsig.scm
+++ b/tests/openpgp/clearsig.scm
@@ -30,12 +30,7 @@
(for-each-p
"Checking signing and verifying plain text messages"
(lambda (source)
- ((if (equal? "plain-3" source)
- ;; plain-3 does not end in a newline, and gpg will add one.
- ;; Therefore, we merely check that the verification is ok.
- check-execution
- ;; Otherwise, we do check that we recover the original file.
- check-identity)
+ (check-identity
source
(check-signing '(--passphrase-fd "0" --clear-sign) usrpass1)))
(append plain-files '("plain-large")))
@@ -65,7 +60,7 @@ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
" #t ())
;; and one with an empty body
- ("" #f ())
+ ("" #t ())
;; and one with one empty line at the end
("line 1
@@ -75,8 +70,10 @@ there is a blank line after this
" #t ())
- ;; I think this file will be constructed wrong (gpg 0.9.3) but it
- ;; should verify okay anyway.
+ ;; Input text with trailing whitespace on any line will have the
+ ;; trailing whitespace stripped when clearsigning (see RFC 4880
+ ;; section 7.1), so verification will succeed, but the outcome
+ ;; will not be identical.
("this is a sig test
" #f ())
--
2.47.2

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