[PATCH] xfs_db: do bounds checking in frag's scanfunc_bmap

[Eric Sandeen <sandeen@xxxxxxxxxxx>]

This is for http://oss.sgi.com/bugzilla/show_bug.cgi?id=842
Bug 842 -  xfs_db crashes on 'frag'

The nrecs in scanfunc_bmap was corrupted & out of bounds, causing
the loop in process_bmbt_reclist to walk well past allocated memory
and eventually segfault.

Add checking to this scanfunc_bmap() similar to that in similar
functions for check, metadump, and repair.

I'm not sure if we can/should print out any more information here...

# db/xfs_db -r -c frag xfs.img 
invalid numrecs (46311) in bmapbtd block
actual 38085, ideal 37731, fragmentation factor 0.93%

Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxxx>
---

diff --git a/db/frag.c b/db/frag.c
index 925863d..bba91ed 100644
--- a/db/frag.c
+++ b/db/frag.c
@@ -437,15 +437,29 @@ scanfunc_bmap(
        int                     i;
        xfs_bmbt_ptr_t          *pp;
        xfs_bmbt_rec_t          *rp;
+       int                     nrecs;
+
+       nrecs = be16_to_cpu(block->bb_numrecs);
 
        if (level == 0) {
+               if (nrecs > mp->m_bmap_dmxr[0]) {
+                       dbprintf(_("invalid numrecs (%u) in %s block\n"),
+                                  nrecs, typtab[btype].name);
+                       return;
+               }
                rp = XFS_BMBT_REC_ADDR(mp, block, 1);
                process_bmbt_reclist((xfs_bmbt_rec_32_t *)rp, 
-                               be16_to_cpu(block->bb_numrecs), extmapp);
+                               nrecs, extmapp);
+               return;
+       }
+
+       if (nrecs > mp->m_bmap_dmxr[1]) {
+               dbprintf(_("invalid numrecs (%u) in %s block\n"),
+                          nrecs, typtab[btype].name);
                return;
        }
        pp = XFS_BMBT_PTR_ADDR(mp, block, 1, mp->m_bmap_dmxr[0]);
-       for (i = 0; i < be16_to_cpu(block->bb_numrecs); i++)
+       for (i = 0; i < nrecs; i++)
                scan_lbtree(be64_to_cpu(pp[i]), level, scanfunc_bmap, extmapp, 
                                                                        btype);
 }