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Code Activity

gpg: Make the use of "--verify FILE" for detached sigs harder.

Browse source 
* g10/openfile.c (open_sigfile): Factor some code out to ...
(get_matching_datafile): new function.
* g10/plaintext.c (hash_datafiles): Do not try to find matching file
in batch mode.
* g10/mainproc.c (check_sig_and_print): Print a warning if a possibly
matching data file is not used by a standard signatures.
--

Allowing to use the abbreviated form for detached signatures is a long
standing bug which has only been noticed by the public with the
release of 2.1.0.  :-(

What we do is to remove the ability to check detached signature in
--batch using the one file abbreviated mode.  This should exhibit
problems in scripts which use this insecure practice.  We also print a
warning if a matching data file exists but was not considered because
the detached signature was actually a standard signature:

  gpgv: Good signature from "Werner Koch (dist sig)"
  gpgv: WARNING: not a detached signature; \
  file 'gnupg-2.1.0.tar.bz2' was NOT verified!

We can only print a warning because it is possible that a standard
signature is indeed to be verified but by coincidence a file with a
matching name is stored alongside the standard signature.

Reported-by: Simon Nicolussi (to gnupg-users on Nov 7)
Signed-off-by: Werner Koch <wk@gnupg.org>

(backported from commit 69384568f6)
This commit is contained in:
Werner Koch 2014-11-14 09:36:19 +01:00
parent da95d0d378
commit a5ca45e616
4 changed files with 115 additions and 39 deletions
Download patch file Download diff file Expand all files Collapse all files

38
g10/mainproc.c
View file

@ -1959,6 +1959,44 @@ check_sig_and_print( CTX c, KBNODE node )
sig->sig_class==0x01?_("textmode"):_("unknown"),
gcry_md_algo_name (sig->digest_algo));
if (!rc && !c->signed_data.used)
{
/* Signature is basically good but we test whether the
deprecated command
gpg --verify FILE.sig
was used instead of
gpg --verify FILE.sig FILE
to verify a detached signature. If we figure out that a
data file with a matching name exists, we print a warning.
The problem is that the first form would also verify a
standard signature. This behavior could be used to
create a made up .sig file for a tarball by creating a
standard signature from a valid detached signature packet
(for example from a signed git tag). Then replace the
sig file on the FTP server along with a changed tarball.
Using the first form the verify command would correctly
verify the signature but don't even consider the tarball. */
kbnode_t n;
char *dfile;
dfile = get_matching_datafile (c->sigfilename);
if (dfile)
{
for (n = c->list; n; n = n->next)
if (n->pkt->pkttype != PKT_SIGNATURE)
break;
if (n)
{
/* Not only signature packets in the tree thus this
is not a detached signature. */
log_info (_("WARNING: not a detached signature; "
"file '%s' was NOT verified!\n"), dfile);
}
xfree (dfile);
}
}
if( rc )
g10_errors_seen = 1;
if( opt.batch && rc )