From d6ca407a27877174c10adfae9dc601bea996cf27 Mon Sep 17 00:00:00 2001
From: Werner Koch <wk@gnupg.org>
Date: Fri, 20 Jun 2014 10:39:26 +0200
Subject: [PATCH] gpg: Avoid infinite loop in uncompressing garbled packets.

* g10/compress.c (do_uncompress): Limit the number of extra FF bytes.
--

A packet like (a3 01 5b ff) leads to an infinite loop.  Using
--max-output won't help if it is a partial packet.  This patch
actually fixes a regression introduced on 1999-05-31 (c34c6769).
Actually it would be sufficient to stuff just one extra 0xff byte.
Given that this problem popped up only after 15 years, I feel safer to
allow for a very few FF bytes.

Thanks to Olivier Levillain and Florian Maury for their detailed
report.
---
 g10/compress.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/g10/compress.c b/g10/compress.c
index 6e412e9ac..0a6e09d46 100644
--- a/g10/compress.c
+++ b/g10/compress.c
@@ -164,7 +164,8 @@ do_uncompress( compress_filter_context_t *zfx, z_stream *zs,
 	       IOBUF a, size_t *ret_len )
 {
     int zrc;
-    int rc=0;
+    int rc = 0;
+    int leave = 0;
     size_t n;
     int nread, count;
     int refill = !zs->avail_in;
@@ -182,13 +183,14 @@ do_uncompress( compress_filter_context_t *zfx, z_stream *zs,
 	    nread = iobuf_read( a, zfx->inbuf + n, count );
 	    if( nread == -1 ) nread = 0;
 	    n += nread;
-	    /* If we use the undocumented feature to suppress
-	     * the zlib header, we have to give inflate an
-	     * extra dummy byte to read */
-	    if( nread < count && zfx->algo == 1 ) {
-		*(zfx->inbuf + n) = 0xFF; /* is it really needed ? */
-		zfx->algo1hack = 1;
+	    /* Algo 1 has no zlib header which requires us to to give
+	     * inflate an extra dummy byte to read. To be on the safe
+	     * side we allow for up to 4 ff bytes.  */
+	    if( nread < count && zfx->algo == 1 && zfx->algo1hack < 4) {
+		*(zfx->inbuf + n) = 0xFF;
+		zfx->algo1hack++;
 		n++;
+                leave = 1;
 	    }
 	    zs->avail_in = n;
 	}
@@ -208,7 +210,8 @@ do_uncompress( compress_filter_context_t *zfx, z_stream *zs,
 	    else
 		log_fatal("zlib inflate problem: rc=%d\n", zrc );
 	}
-    } while( zs->avail_out && zrc != Z_STREAM_END && zrc != Z_BUF_ERROR );
+    } while (zs->avail_out && zrc != Z_STREAM_END && zrc != Z_BUF_ERROR
+             && !leave);
 
     *ret_len = zfx->outbufsize - zs->avail_out;
     if( DBG_FILTER )