[SECURITY PATCH 22/28] lvm: Fix two more potential data-dependent alloc overflows

[Daniel Kiper]

From: Peter Jones <pjones@redhat.com>

It appears to be possible to make a (possibly invalid) lvm PV with
a metadata size field that overflows our type when adding it to the
address we've allocated. Even if it doesn't, it may be possible to do so
with the math using the outcome of that as an operand. Check them both.

Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/disk/lvm.c | 48 ++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 40 insertions(+), 8 deletions(-)

diff --git a/grub-core/disk/lvm.c b/grub-core/disk/lvm.c
index 48e36b4f3..753545146 100644
--- a/grub-core/disk/lvm.c
+++ b/grub-core/disk/lvm.c
@@ -25,6 +25,7 @@
 #include <grub/lvm.h>
 #include <grub/partition.h>
 #include <grub/i18n.h>
+#include <grub/safemath.h>
 
 #ifdef GRUB_UTIL
 #include <grub/emu/misc.h>
@@ -138,10 +139,11 @@ grub_lvm_detect (grub_disk_t disk,
 {
   grub_err_t err;
   grub_uint64_t mda_offset, mda_size;
+  grub_size_t ptr;
   char buf[GRUB_LVM_LABEL_SIZE];
   char vg_id[GRUB_LVM_ID_STRLEN+1];
   char pv_id[GRUB_LVM_ID_STRLEN+1];
-  char *metadatabuf, *vgname;
+  char *metadatabuf, *mda_end, *vgname;
   const char *p, *q;
   struct grub_lvm_label_header *lh = (struct grub_lvm_label_header *) buf;
   struct grub_lvm_pv_header *pvh;
@@ -242,19 +244,31 @@ grub_lvm_detect (grub_disk_t disk,
                   grub_le_to_cpu64 (rlocn->size) -
                   grub_le_to_cpu64 (mdah->size));
     }
-  p = q = metadatabuf + grub_le_to_cpu64 (rlocn->offset);
 
-  while (*q != ' ' && q < metadatabuf + mda_size)
-    q++;
-
-  if (q == metadatabuf + mda_size)
+  if (grub_add ((grub_size_t)metadatabuf,
+               (grub_size_t)grub_le_to_cpu64 (rlocn->offset),
+               &ptr))
     {
+ error_parsing_metadata:
 #ifdef GRUB_UTIL
       grub_util_info ("error parsing metadata");
 #endif
       goto fail2;
     }
 
+  p = q = (char *)ptr;
+
+  if (grub_add ((grub_size_t)metadatabuf, (grub_size_t)mda_size, &ptr))
+    goto error_parsing_metadata;
+
+  mda_end = (char *)ptr;
+
+  while (*q != ' ' && q < mda_end)
+    q++;
+
+  if (q == mda_end)
+    goto error_parsing_metadata;
+
   vgname_len = q - p;
   vgname = grub_malloc (vgname_len + 1);
   if (!vgname)
@@ -406,8 +420,26 @@ grub_lvm_detect (grub_disk_t disk,
              {
                const char *iptr;
                char *optr;
-               lv->fullname = grub_malloc (sizeof ("lvm/") - 1 + 2 * vgname_len
-                                           + 1 + 2 * s + 1);
+
+               /*
+                * This is kind of hard to read with our safe (but rather
+                * baroque) math primatives, but it boils down to:
+                *
+                *   sz0 = vgname_len * 2 + 1 +
+                *         s * 2 + 1 +
+                *         sizeof ("lvm/") - 1;
+                */
+               grub_size_t sz0 = vgname_len, sz1 = s;
+
+               if (grub_mul (sz0, 2, &sz0) ||
+                   grub_add (sz0, 1, &sz0) ||
+                   grub_mul (sz1, 2, &sz1) ||
+                   grub_add (sz1, 1, &sz1) ||
+                   grub_add (sz0, sz1, &sz0) ||
+                   grub_add (sz0, sizeof ("lvm/") - 1, &sz0))
+                 goto lvs_fail;
+
+               lv->fullname = grub_malloc (sz0);
                if (!lv->fullname)
                  goto lvs_fail;
 
-- 
2.11.0