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

* 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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
g10/main.h
View File

@ -253,7 +253,8 @@ int overwrite_filep( const char *fname );
char *make_outfile_name( const char *iname );
char *ask_outfile_name( const char *name, size_t namelen );
int open_outfile( const char *iname, int mode, iobuf_t *a );
iobuf_t open_sigfile( const char *iname, progress_filter_context_t *pfx );
char *get_matching_datafile (const char *sigfilename);
iobuf_t open_sigfile (const char *sigfilename, progress_filter_context_t *pfx);
void try_make_homedir( const char *fname );
/*-- seskey.c --*/

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 )

81
g10/openfile.c
View File

@ -287,41 +287,70 @@ open_outfile( const char *iname, int mode, IOBUF *a )
}
/* Find a matching data file for the signature file SIGFILENAME and
return it as a malloced string. If no matching data file is found,
return NULL. */
char *
get_matching_datafile (const char *sigfilename)
{
char *fname = NULL;
size_t len;
if (iobuf_is_pipe_filename (sigfilename))
return NULL;
len = strlen (sigfilename);
if (len > 4
&& (!strcmp (sigfilename + len - 4, EXTSEP_S "sig")
|| (len > 5 && !strcmp(sigfilename + len - 5, EXTSEP_S "sign"))
|| !strcmp(sigfilename + len - 4, EXTSEP_S "asc")))
{
fname = xstrdup (sigfilename);
fname[len-(fname[len-1]=='n'?5:4)] = 0 ;
if (access (fname, R_OK ))
{
/* Not found or other error. */
xfree (fname);
fname = NULL;
}
}
return fname;
}
/****************
* Try to open a file without the extension ".sig" or ".asc"
* Return NULL if such a file is not available.
*/
IOBUF
open_sigfile( const char *iname, progress_filter_context_t *pfx )
iobuf_t
open_sigfile (const char *sigfilename, progress_filter_context_t *pfx)
{
IOBUF a = NULL;
size_t len;
iobuf_t a = NULL;
char *buf;
if( !iobuf_is_pipe_filename (iname) ) {
len = strlen(iname);
if( len > 4 && ( !strcmp(iname + len - 4, EXTSEP_S "sig")
|| ( len > 5 && !strcmp(iname + len - 5, EXTSEP_S "sign") )
|| !strcmp(iname + len - 4, EXTSEP_S "asc")) ) {
char *buf;
buf = xstrdup(iname);
buf[len-(buf[len-1]=='n'?5:4)] = 0 ;
a = iobuf_open( buf );
if (a && is_secured_file (iobuf_get_fd (a)))
{
iobuf_close (a);
a = NULL;
errno = EPERM;
}
if( a && opt.verbose )
log_info(_("assuming signed data in `%s'\n"), buf );
if (a && pfx)
handle_progress (pfx, a, buf);
xfree(buf);
}
buf = get_matching_datafile (sigfilename);
if (buf)
{
a = iobuf_open (buf);
if (a && is_secured_file (iobuf_get_fd (a)))
{
iobuf_close (a);
a = NULL;
gpg_err_set_errno (EPERM);
}
if (a)
log_info (_("assuming signed data in '%s'\n"), buf);
if (a && pfx)
handle_progress (pfx, a, buf);
xfree (buf);
}
return a;
return a;
}
/****************
* Copy the option file skeleton to the given directory.
*/

32
g10/plaintext.c
View File

@ -546,17 +546,25 @@ hash_datafiles( gcry_md_hd_t md, gcry_md_hd_t md2, strlist_t files,
pfx = new_progress_context ();
if( !files ) {
/* check whether we can open the signed material */
fp = open_sigfile( sigfilename, pfx );
if( fp ) {
do_hash( md, md2, fp, textmode );
iobuf_close(fp);
release_progress_context (pfx);
return 0;
}
log_error (_("no signed data\n"));
release_progress_context (pfx);
return gpg_error (GPG_ERR_NO_DATA);
/* Check whether we can open the signed material. We avoid
trying to open a file if run in batch mode. This assumed
data file for a sig file feature is just a convenience thing
for the command line and the user needs to read possible
warning messages. */
if (!opt.batch)
{
fp = open_sigfile( sigfilename, pfx );
if( fp )
{
do_hash( md, md2, fp, textmode );
iobuf_close(fp);
release_progress_context (pfx);
return 0;
}
}
log_error (_("no signed data\n"));
release_progress_context (pfx);
return gpg_error (GPG_ERR_NO_DATA);
}
@ -615,7 +623,7 @@ hash_datafile_by_fd ( gcry_md_hd_t md, gcry_md_hd_t md2, int data_fd,
do_hash ( md, md2, fp, textmode);
iobuf_close(fp);
release_progress_context (pfx);
return 0;
}