[libgsf] GsfInfileOle: improve handling of broken files.

[Morten Welinder <mortenw src gnome org>]

commit c477afcaf9dcf94dc8abe64256cba1e5d554e1e9
Author: Morten Welinder <terra gnome org>
Date:   Sat Apr 20 15:30:46 2013 -0400

    GsfInfileOle: improve handling of broken files.

 ChangeLog              |  8 ++++++++
 NEWS                   |  1 +
 gsf/gsf-infile-msole.c | 39 ++++++++++++++++++++-------------------
 3 files changed, 29 insertions(+), 19 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 60f8cd0..4bedd41 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2013-04-20  Morten Welinder  <terra gnome org>
+
+       * gsf/gsf-infile-msole.c (gsf_infile_msole_read): Don't read
+       beyond the number of bat blocks we have.  (We can have less blocks
+       than expected when the bat chain is found to be circular.)  Don't
+       optimize seek; the lower levels will do that just fine.
+       (ole_make_bat): Simplify.
+
 2013-03-08  Morten Welinder  <terra gnome org>
 
        * gsf/gsf-input.c (gsf_input_set_modtime): Change to transfer-none
diff --git a/NEWS b/NEWS
index 97a1e00..138a2e4 100644
--- a/NEWS
+++ b/NEWS
@@ -11,6 +11,7 @@ Morten:
        * Add modtime support for GsfOutput, GsfOutputStdio, GsfOutputGzip.
        * Add modtime support for GsfOutfileZip, GsfOutfileMSOle.
        * Enhance gsf tool to print modtime and create archives with modtime.
+       * Improve handling of broken OLE2 files.
 
 --------------------------------------------------------------------------
 libgsf 1.14.26
diff --git a/gsf/gsf-infile-msole.c b/gsf/gsf-infile-msole.c
index 2ed7b88..b7dc919 100644
--- a/gsf/gsf-infile-msole.c
+++ b/gsf/gsf-infile-msole.c
@@ -161,25 +161,22 @@ ole_make_bat (MSOleBAT const *metabat, size_t size_guess, guint32 block,
        guint8 *used = (guint8*)g_alloca (1 + metabat->num_blocks / 8);
        memset (used, 0, 1 + metabat->num_blocks / 8);
 
-       if (block < metabat->num_blocks)
-               do {
-                       /* Catch cycles in the bat list */
-                       if (used[block/8] & (1 << (block & 0x7)))
-                               break;
-                       used[block/8] |= 1 << (block & 0x7);
-
-                       g_array_append_val (bat, block);
-                       block = metabat->block [block];
-               } while (block < metabat->num_blocks);
+       while (block < metabat->num_blocks) {
+               /* Catch cycles in the bat list */
+               if (used[block/8] & (1 << (block & 0x7)))
+                       break;
+               used[block/8] |= 1 << (block & 0x7);
 
-       res->block = NULL;
+               g_array_append_val (bat, block);
+               block = metabat->block [block];
+       }
 
        res->num_blocks = bat->len;
        res->block = (guint32 *) (gpointer) g_array_free (bat, FALSE);
 
        if (block != BAT_MAGIC_END_OF_CHAIN) {
                g_warning ("This OLE2 file is invalid.\n"
-                          "The Block Allocation Table for one of the streams had %x instead of a terminator 
(%x).\n"
+                          "The Block Allocation Table for one of the streams had 0x%08x instead of a 
terminator (0x%08x).\n"
                           "We might still be able to extract some data, but you'll want to check the file.",
                           block, BAT_MAGIC_END_OF_CHAIN);
        }
@@ -705,17 +702,21 @@ gsf_infile_msole_read (GsfInput *input, size_t num_bytes, guint8 *buffer)
        last_block = OLE_BIG_BLOCK (input->cur_offset + num_bytes - 1, ole);
        offset = input->cur_offset & ole->info->bb.filter;
 
-       /* optimization : are all the raw blocks contiguous */
+       if (last_block >= ole->bat.num_blocks)
+               return NULL;
+
+       /* Optimization: are all the raw blocks contiguous?  */
        i = first_block;
-       raw_block = ole->bat.block [i];
+       raw_block = ole->bat.block[i];
+       if (FALSE && first_block != last_block)
+               g_printerr ("Check if %ld-%ld of %d are contiguous.\n",
+                           first_block, last_block,
+                           ole->bat.num_blocks);
        while (++i <= last_block && ++raw_block == ole->bat.block [i])
                ;
        if (i > last_block) {
-               /* optimization don't seek if we don't need to */
-               if (ole->cur_block != first_block) {
-                       if (!ole_seek_block (ole, ole->bat.block [first_block], offset))
-                               return NULL;
-               }
+               if (!ole_seek_block (ole, ole->bat.block [first_block], offset))
+                       return NULL;
                ole->cur_block = last_block;
                return gsf_input_read (ole->input, num_bytes, buffer);
        }