gpg: Detect already compressed data also when using a pipe.

* common/iobuf.c (file_filter_ctx_t): Add fields for the peek feature.
(file_filter): Implement peeking.
(iobuf_ioctl): Add new IOBUF_IOCTL_PEEK.
* common/iobuf.h (IOBUF_IOCTL_PEEK, IOBUFCTRL_PEEK): New.
* common/miscellaneous.c (is_file_compressed): Rewrite.  Detect PDF.
* g10/encrypt.c (encrypt_simple): Peek before detecting compression.
(encrypt_crypt): Ditto.
* g10/sign.c (sign_file): Also detect already compressed data.

* g10/options.h (opt): Add explicit_compress_option.
* g10/gpg.c (main): Set opt.explicit_compress_option for -z.

--

Note that this patch also introduces a compression check for signing
which was never done in the past.

GnuPG-bug-id: 6332

9 files changed, 201 insertions, 64 deletions

diff --git a/common/iobuf.c b/common/iobuf.c
index ab8368b54..62cde27f9 100644
--- a/common/iobuf.c
+++ b/common/iobuf.c
@@ -1,7 +1,7 @@
 /* iobuf.c  -  File Handling for OpenPGP.
  * Copyright (C) 1998, 1999, 2000, 2001, 2003, 2004, 2006, 2007, 2008,
  *               2009, 2010, 2011  Free Software Foundation, Inc.
- * Copyright (C) 2015  g10 Code GmbH
+ * Copyright (C) 2015, 2023  g10 Code GmbH
  *
  * This file is part of GnuPG.
  *
@@ -95,6 +95,9 @@ typedef struct
   int eof_seen;
   int delayed_rc;
   int print_only_name; /* Flags indicating that fname is not a real file.  */
+  char peeked[32];     /* Read ahead buffer.  */
+  byte npeeked;        /* Number of bytes valid in peeked.  */
+  byte upeeked;        /* Number of bytes used from peeked.  */
   char fname[1];       /* Name of the file.  */
 } file_filter_ctx_t;
 
@@ -458,7 +461,16 @@ file_filter (void *opaque, int control, iobuf_t chain, byte * buf,
   if (control == IOBUFCTRL_UNDERFLOW)
     {
       log_assert (size); /* We need a buffer.  */
-      if (a->eof_seen)
+      if (a->npeeked > a->upeeked)
+        {
+          nbytes = a->npeeked - a->upeeked;
+          if (nbytes > size)
+            nbytes = size;
+          memcpy (buf, a->peeked + a->upeeked, nbytes);
+          a->upeeked += nbytes;
+          *ret_len = nbytes;
+        }
+      else if (a->eof_seen)
 	{
 	  rc = -1;
 	  *ret_len = 0;
@@ -596,6 +608,73 @@ file_filter (void *opaque, int control, iobuf_t chain, byte * buf,
       a->delayed_rc = 0;
       a->keep_open = 0;
       a->no_cache = 0;
+      a->npeeked = 0;
+      a->upeeked = 0;
+    }
+  else if (control == IOBUFCTRL_PEEK)
+    {
+      /* Peek on the input.  */
+#ifdef HAVE_W32_SYSTEM
+      unsigned long nread;
+
+      nbytes = 0;
+      if (!ReadFile (f, a->peeked, sizeof a->peeked, &nread, NULL))
+        {
+          int ec = (int) GetLastError ();
+          if (ec != ERROR_BROKEN_PIPE)
+            {
+              rc = gpg_error_from_errno (ec);
+              log_error ("%s: read error: ec=%d\n", a->fname, ec);
+            }
+          a->npeeked = 0;
+        }
+      else if (!nread)
+        {
+          a->eof_seen = 1;
+          a->npeeked = 0;
+        }
+      else
+        {
+          a->npeeked = nread;
+        }
+
+#else /* Unix */
+
+      int n;
+
+    peek_more:
+      do
+        {
+          n = read (f, a->peeked + a->npeeked, sizeof a->peeked - a->npeeked);
+        }
+      while (n == -1 && errno == EINTR);
+      if (n > 0)
+        {
+          a->npeeked += n;
+          if (a->npeeked < sizeof a->peeked)
+            goto peek_more;
+        }
+      else if (!n) /* eof */
+        {
+          if (a->npeeked)
+            a->delayed_rc = -1;
+          else
+            a->eof_seen = 1;
+        }
+      else /* error */
+        {
+          rc = gpg_error_from_syserror ();
+          if (gpg_err_code (rc) != GPG_ERR_EPIPE)
+            log_error ("%s: read error: %s\n", a->fname, gpg_strerror (rc));
+          if (a->npeeked)
+            a->delayed_rc = rc;
+        }
+#endif /* Unix */
+
+      size = a->npeeked < size? a->npeeked : size;
+      memcpy (buf, a->peeked, size);
+      *ret_len = size;
+      rc = 0;  /* Return success - the user needs to check ret_len.  */
     }
   else if (control == IOBUFCTRL_DESC)
     {
@@ -1576,6 +1655,25 @@ iobuf_ioctl (iobuf_t a, iobuf_ioctl_t cmd, int intval, void *ptrval)
           return fd_cache_synchronize (ptrval);
         }
     }
+  else if (cmd == IOBUF_IOCTL_PEEK)
+    {
+      /* Peek at a justed opened file.  Use this only directly after a
+       * file has been opened for reading.  Don't use it after you did
+       * a seek.  This works only if just file filter has been
+       * pushed.  Expects a buffer wit size INTVAL at PTRVAL and returns
+       * the number of bytes put into the buffer.  */
+      if (DBG_IOBUF)
+	log_debug ("iobuf-%d.%d: ioctl '%s' peek\n",
+		   a ? a->no : -1, a ? a->subno : -1, iobuf_desc (a, desc));
+      if (a->filter == file_filter && ptrval && intval)
+        {
+          file_filter_ctx_t *fcx = a->filter_ov;
+          size_t len = intval;
+
+          if (!file_filter (fcx, IOBUFCTRL_PEEK, NULL, ptrval, &len))
+            return (int)len;
+        }
+    }
 
 
   return -1;
diff --git a/common/iobuf.h b/common/iobuf.h
index f527fbf16..c132c2f3c 100644
--- a/common/iobuf.h
+++ b/common/iobuf.h
@@ -106,6 +106,7 @@ enum
     IOBUFCTRL_FLUSH     = 4,
     IOBUFCTRL_DESC	= 5,
     IOBUFCTRL_CANCEL    = 6,
+    IOBUFCTRL_PEEK      = 7,
     IOBUFCTRL_USER	= 16
   };
 
@@ -116,7 +117,8 @@ typedef enum
     IOBUF_IOCTL_KEEP_OPEN        = 1, /* Uses intval.  */
     IOBUF_IOCTL_INVALIDATE_CACHE = 2, /* Uses ptrval.  */
     IOBUF_IOCTL_NO_CACHE         = 3, /* Uses intval.  */
-    IOBUF_IOCTL_FSYNC            = 4  /* Uses ptrval.  */
+    IOBUF_IOCTL_FSYNC            = 4, /* Uses ptrval.  */
+    IOBUF_IOCTL_PEEK             = 5  /* Uses intval and ptrval.  */
   } iobuf_ioctl_t;
 
 enum iobuf_use
diff --git a/common/miscellaneous.c b/common/miscellaneous.c
index df6b68784..60ac4b4df 100644
--- a/common/miscellaneous.c
+++ b/common/miscellaneous.c
@@ -418,7 +418,7 @@ decode_c_string (const char *src)
 /* Check whether (BUF,LEN) is valid header for an OpenPGP compressed
  * packet.  LEN should be at least 6.  */
 static int
-is_openpgp_compressed_packet (unsigned char *buf, size_t len)
+is_openpgp_compressed_packet (const unsigned char *buf, size_t len)
 {
   int c, ctb, pkttype;
   int lenbytes;
@@ -460,63 +460,46 @@ is_openpgp_compressed_packet (unsigned char *buf, size_t len)
 
 
 /*
- * Check if the file is compressed.
+ * Check if the file is compressed.  You need to pass the first bytes
+ * of the file as (BUF,BUFLEN).  Returns true if the buffer seems to
+ * be compressed.
  */
 int
-is_file_compressed (const char *s, int *ret_rc)
+is_file_compressed (const byte *buf, unsigned int buflen)
 {
-    iobuf_t a;
-    byte buf[6];
-    int i;
-    int rc = 0;
-    int overflow;
-
-    struct magic_compress_s {
-        size_t len;
-        byte magic[4];
-    } magic[] = {
-        { 3, { 0x42, 0x5a, 0x68, 0x00 } }, /* bzip2 */
-        { 3, { 0x1f, 0x8b, 0x08, 0x00 } }, /* gzip */
-        { 4, { 0x50, 0x4b, 0x03, 0x04 } }, /* (pk)zip */
-    };
-
-    if ( iobuf_is_pipe_filename (s) || !ret_rc )
-        return 0; /* We can't check stdin or no file was given */
-
-    a = iobuf_open( s );
-    if ( a == NULL ) {
-        *ret_rc = gpg_error_from_syserror ();
-        return 0;
-    }
-    iobuf_ioctl (a, IOBUF_IOCTL_NO_CACHE, 1, NULL);
+  int i;
 
-    if ( iobuf_get_filelength( a, &overflow ) < 6 && !overflow) {
-        *ret_rc = 0;
-        goto leave;
-    }
+  struct magic_compress_s
+  {
+    byte len;
+    byte magic[5];
+  } magic[] =
+      {
+       { 3, { 0x42, 0x5a, 0x68, 0x00 } }, /* bzip2 */
+       { 3, { 0x1f, 0x8b, 0x08, 0x00 } }, /* gzip */
+       { 4, { 0x50, 0x4b, 0x03, 0x04 } }, /* (pk)zip */
+       { 5, { '%', 'P', 'D', 'F', '-'} }  /* PDF */
+  };
 
-    if ( iobuf_read( a, buf, 6 ) == -1 ) {
-        *ret_rc = a->error;
-        goto leave;
+  if ( buflen < 6 )
+    {
+      return 0;  /* Too short to check - assume uncompressed.  */
     }
 
-    for ( i = 0; i < DIM( magic ); i++ ) {
-        if ( !memcmp( buf, magic[i].magic, magic[i].len ) ) {
-            *ret_rc = 0;
-            rc = 1;
-            goto leave;
+  for ( i = 0; i < DIM (magic); i++ )
+    {
+      if ( !memcmp( buf, magic[i].magic, magic[i].len ))
+        {
+          return 1; /* Is compressed.  */
         }
     }
 
-    if (is_openpgp_compressed_packet (buf, 6))
-      {
-        *ret_rc = 0;
-        rc = 1;
-      }
+  if (buflen >= 6 && is_openpgp_compressed_packet (buf, buflen))
+    {
+      return 1; /* Already compressed.  */
+    }
 
- leave:
-    iobuf_close( a );
-    return rc;
+  return 0;  /* Not detected as compressed.  */
 }
 
 
diff --git a/common/util.h b/common/util.h
index 6978ab896..d80e4fb25 100644
--- a/common/util.h
+++ b/common/util.h
@@ -359,7 +359,7 @@ char *try_make_printable_string (const void *p, size_t n, int delim);
 char *make_printable_string (const void *p, size_t n, int delim);
 char *decode_c_string (const char *src);
 
-int is_file_compressed (const char *s, int *ret_rc);
+int is_file_compressed (const byte *buf, unsigned int buflen);
 
 int match_multistr (const char *multistr,const char *match);
 
diff --git a/doc/gpg.texi b/doc/gpg.texi
index 804ecf94a..457088eb3 100644
--- a/doc/gpg.texi
+++ b/doc/gpg.texi
@@ -635,12 +635,13 @@ The @option{--dearmor} command can also be used to dearmor PEM armors.
 
 @item --unwrap
 @opindex unwrap
-This command is similar to @option{--decrypt} with the change that the
+This command is similar to @option{--decrypt} with the difference that the
 output is not the usual plaintext but the original message with the
-decryption layer removed.  Thus the output will be an OpenPGP data
+encryption layer removed.  Thus the output will be an OpenPGP data
 structure which often means a signed OpenPGP message.  Note that this
 command may or may not remove a compression layer which is often found
-beneath the encryption layer.
+beneath the encryption layer.  Without the option @option{--output}
+the result is written to a file with the suffix stripped.
 
 @item --tofu-policy @{auto|good|unknown|bad|ask@}  @var{keys}
 @opindex tofu-policy
@@ -860,9 +861,10 @@ line.
   @opindex keyedit:tsign
   Make a trust signature. This is a signature that combines the notions
   of certification (like a regular signature), and trust (like the
-  "trust" command). It is generally only useful in distinct communities
-  or groups.  For more information please read the sections
-  ``Trust Signature'' and ``Regular Expression'' in RFC-4880.
+  "trust" command). It is generally useful in distinct communities
+  or groups to implement the concept of a Trusted Introducer.  For
+  more information please read the sections ``Trust Signature'' and
+  ``Regular Expression'' in RFC-4880.
 @end table
 
 @c man:.RS
@@ -1658,6 +1660,16 @@ for the BZIP2 compression algorithm (defaulting to 6 as well). This is a
 different option from @option{--compress-level} since BZIP2 uses a
 significant amount of memory for each additional compression level.
 @option{-z} sets both. A value of 0 for @var{n} disables compression.
+A value of -1 forces compression using the default level.
+
+Except for the @option{--store} command compression is always used
+unless @command{gpg} detects that the input is already compressed.  To
+inhibit the use of compression use @option{-z0}; to force compression
+use @option{-z-1} or option @option{z} with another compression level
+than the default as indicated by -1.  Note that this overriding of the
+default deection works only with @option{z} and not with the long
+variant of this option.
+
 
 @item --bzip2-decompress-lowmem
 @opindex bzip2-decompress-lowmem
diff --git a/g10/encrypt.c b/g10/encrypt.c
index d0e142714..687b4344e 100644
--- a/g10/encrypt.c
+++ b/g10/encrypt.c
@@ -1,7 +1,7 @@
 /* encrypt.c - Main encryption driver
  * Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
  *               2006, 2009 Free Software Foundation, Inc.
- * Copyright (C) 2016 g10 Code GmbH
+ * Copyright (C) 2016, 2023 g10 Code GmbH
  *
  * This file is part of GnuPG.
  *
@@ -17,6 +17,7 @@
  *
  * You should have received a copy of the GNU General Public License
  * along with this program; if not, see <https://www.gnu.org/licenses/>.
+ * SPDX-License-Identifier: GPL-3.0-or-later
  */
 
 #include <config.h>
@@ -409,6 +410,8 @@ encrypt_simple (const char *filename, int mode, int use_seskey)
   text_filter_context_t tfx;
   progress_filter_context_t *pfx;
   int do_compress = !!default_compress_algo();
+  char peekbuf[32];
+  int  peekbuflen;
 
   if (!gnupg_rng_is_compliant (opt.compliance))
     {
@@ -445,6 +448,14 @@ encrypt_simple (const char *filename, int mode, int use_seskey)
       return rc;
     }
 
+  peekbuflen = iobuf_ioctl (inp, IOBUF_IOCTL_PEEK, sizeof peekbuf, peekbuf);
+  if (peekbuflen < 0)
+    {
+      peekbuflen = 0;
+      if (DBG_FILTER)
+        log_debug ("peeking at input failed\n");
+    }
+
   handle_progress (pfx, inp, filename);
 
   if (opt.textmode)
@@ -509,10 +520,11 @@ encrypt_simple (const char *filename, int mode, int use_seskey)
   if (do_compress
       && cfx.dek
       && (cfx.dek->use_mdc || cfx.dek->use_aead)
-      && is_file_compressed(filename, &rc))
+      && !opt.explicit_compress_option
+      && is_file_compressed (peekbuf, peekbuflen))
     {
       if (opt.verbose)
-        log_info(_("'%s' already compressed\n"), filename);
+        log_info(_("'%s' already compressed\n"), filename? filename: "[stdin]");
       do_compress = 0;
     }
 
@@ -780,6 +792,8 @@ encrypt_crypt (ctrl_t ctrl, int filefd, const char *filename,
   progress_filter_context_t *pfx;
   PK_LIST pk_list;
   int do_compress;
+  char peekbuf[32];
+  int  peekbuflen;
 
   if (filefd != -1 && filename)
     return gpg_error (GPG_ERR_INV_ARG);  /* Both given.  */
@@ -852,6 +866,14 @@ encrypt_crypt (ctrl_t ctrl, int filefd, const char *filename,
   if (opt.verbose)
     log_info (_("reading from '%s'\n"), iobuf_get_fname_nonnull (inp));
 
+  peekbuflen = iobuf_ioctl (inp, IOBUF_IOCTL_PEEK, sizeof peekbuf, peekbuf);
+  if (peekbuflen < 0)
+    {
+      peekbuflen = 0;
+      if (DBG_FILTER)
+        log_debug ("peeking at input failed\n");
+    }
+
   handle_progress (pfx, inp, filename);
 
   if (opt.textmode)
@@ -884,10 +906,11 @@ encrypt_crypt (ctrl_t ctrl, int filefd, const char *filename,
    * ciphertext attacks. */
   if (do_compress
       && (cfx.dek->use_mdc || cfx.dek->use_aead)
-      && is_file_compressed (filename, &rc2))
+      && !opt.explicit_compress_option
+      && is_file_compressed (peekbuf, peekbuflen))
     {
       if (opt.verbose)
-        log_info(_("'%s' already compressed\n"), filename);
+        log_info(_("'%s' already compressed\n"), filename? filename: "[stdin]");
       do_compress = 0;
     }
   if (rc2)
diff --git a/g10/gpg.c b/g10/gpg.c
index 68c0454ee..de40d3828 100644
--- a/g10/gpg.c
+++ b/g10/gpg.c
@@ -3203,6 +3203,7 @@ main (int argc, char **argv)
 	  case oCompress:
 	    /* this is the -z command line option */
 	    opt.compress_level = opt.bz2_compress_level = pargs.r.ret_int;
+            opt.explicit_compress_option = 1;
 	    break;
 	  case oCompressLevel: opt.compress_level = pargs.r.ret_int; break;
 	  case oBZ2CompressLevel: opt.bz2_compress_level = pargs.r.ret_int; break;
diff --git a/g10/options.h b/g10/options.h
index c10862687..fa649f8ca 100644
--- a/g10/options.h
+++ b/g10/options.h
@@ -98,6 +98,7 @@ struct
   int def_digest_algo;
   int cert_digest_algo;
   int compress_algo;
+  int explicit_compress_option; /* A compress option was explicitly given. */
   int compress_level;
   int bz2_compress_level;
   int bz2_decompress_lowmem;
diff --git a/g10/sign.c b/g10/sign.c
index 385254987..a66410ebd 100644
--- a/g10/sign.c
+++ b/g10/sign.c
@@ -1037,6 +1037,9 @@ sign_file (ctrl_t ctrl, strlist_t filenames, int detached, strlist_t locusr,
   int multifile = 0;
   u32 duration=0;
   pt_extra_hash_data_t extrahash = NULL;
+  char peekbuf[32];
+  int  peekbuflen = 0;
+
 
   pfx = new_progress_context ();
   afx = new_armor_context ();
@@ -1095,6 +1098,14 @@ sign_file (ctrl_t ctrl, strlist_t filenames, int detached, strlist_t locusr,
           goto leave;
 	}
 
+      peekbuflen = iobuf_ioctl (inp, IOBUF_IOCTL_PEEK, sizeof peekbuf, peekbuf);
+      if (peekbuflen < 0)
+        {
+          peekbuflen = 0;
+          if (DBG_FILTER)
+            log_debug ("peeking at input failed\n");
+        }
+
       handle_progress (pfx, inp, fname);
     }
 
@@ -1251,8 +1262,14 @@ sign_file (ctrl_t ctrl, strlist_t filenames, int detached, strlist_t locusr,
     {
       int compr_algo = opt.compress_algo;
 
-      /* If not forced by user */
-      if (compr_algo==-1)
+      if (!opt.explicit_compress_option
+          && is_file_compressed (peekbuf, peekbuflen))
+        {
+          if (opt.verbose)
+            log_info(_("'%s' already compressed\n"), fname? fname: "[stdin]");
+          compr_algo = 0;
+        }
+      else if (compr_algo==-1)
         {
           /* If we're not encrypting, then select_algo_from_prefs
            * will fail and we'll end up with the default.  If we are