[PATCH] Allocate LVM metadata buffer from raw contents

[Michael Chang]

The size reserved for on disk LVM metadata area can be exceedingly large that
may trigger out of memory error for allocating buffer based on it. Refine the
buffer allocation to use size of raw LVM metadata contents and read them from
within the metadata area as we only need to parse the JSON formatted contents
rather than the entire metadata area. This reduced the size significantly and
the likelihood to out of memory error.
---
 grub-core/disk/lvm.c | 65 ++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 45 insertions(+), 20 deletions(-)

diff --git a/grub-core/disk/lvm.c b/grub-core/disk/lvm.c
index 7b265c7..47aae05 100644
--- a/grub-core/disk/lvm.c
+++ b/grub-core/disk/lvm.c
@@ -102,9 +102,11 @@ grub_lvm_detect (grub_disk_t disk,
 {
   grub_err_t err;
   grub_uint64_t mda_offset, mda_size;
+  grub_uint64_t mda_raw_offset, mda_raw_size;
   char buf[GRUB_LVM_LABEL_SIZE];
   char vg_id[GRUB_LVM_ID_STRLEN+1];
   char pv_id[GRUB_LVM_ID_STRLEN+1];
+  char mdah_buf[sizeof (struct grub_lvm_mda_header) + sizeof (struct 
grub_lvm_raw_locn)];
   char *metadatabuf, *p, *q, *vgname;
   struct grub_lvm_label_header *lh = (struct grub_lvm_label_header *) buf;
   struct grub_lvm_pv_header *pvh;
@@ -167,21 +169,15 @@ grub_lvm_detect (grub_disk_t disk,
 
   dlocn++;
   mda_offset = grub_le_to_cpu64 (dlocn->offset);
-  mda_size = grub_le_to_cpu64 (dlocn->size);
 
   /* It's possible to have multiple copies of metadata areas, we just use the
      first one.  */
-
-  /* Allocate buffer space for the circular worst-case scenario. */
-  metadatabuf = grub_malloc (2 * mda_size);
-  if (! metadatabuf)
+  err = grub_disk_read (disk, 0, mda_offset, sizeof (mdah_buf), mdah_buf);
+  if (err)
     goto fail;
 
-  err = grub_disk_read (disk, 0, mda_offset, mda_size, metadatabuf);
-  if (err)
-    goto fail2;
+  mdah = (struct grub_lvm_mda_header *) mdah_buf;
 
-  mdah = (struct grub_lvm_mda_header *) metadatabuf;
   if ((grub_strncmp ((char *)mdah->magic, GRUB_LVM_FMTT_MAGIC,
                     sizeof (mdah->magic)))
       || (grub_le_to_cpu32 (mdah->version) != GRUB_LVM_FMTT_VERSION))
@@ -191,26 +187,55 @@ grub_lvm_detect (grub_disk_t disk,
 #ifdef GRUB_UTIL
       grub_util_info ("unknown LVM metadata header");
 #endif
-      goto fail2;
+      goto fail;
     }
 
   rlocn = mdah->raw_locns;
-  if (grub_le_to_cpu64 (rlocn->offset) + grub_le_to_cpu64 (rlocn->size) >
-      grub_le_to_cpu64 (mdah->size))
+
+  mda_size = grub_le_to_cpu64 (mdah->size);
+  mda_raw_size = grub_le_to_cpu64 (rlocn->size);
+  mda_raw_offset = grub_le_to_cpu64 (rlocn->offset);
+
+  metadatabuf = grub_malloc (mda_raw_size);
+
+  if (! metadatabuf)
+    goto fail;
+
+  if (mda_raw_offset > mda_size)
+    goto fail2;
+
+  if (mda_raw_offset + mda_raw_size > mda_size)
     {
+      err = grub_disk_read (disk, 0,
+                           mda_offset + mda_raw_offset,
+                           mda_size - mda_raw_offset,
+                           metadatabuf);
+      if (err)
+       goto fail2;
+
       /* Metadata is circular. Copy the wrap in place. */
-      grub_memcpy (metadatabuf + mda_size,
-                  metadatabuf + GRUB_LVM_MDA_HEADER_SIZE,
-                  grub_le_to_cpu64 (rlocn->offset) +
-                  grub_le_to_cpu64 (rlocn->size) -
-                  grub_le_to_cpu64 (mdah->size));
+      err = grub_disk_read (disk, 0,
+                           mda_offset + GRUB_LVM_MDA_HEADER_SIZE,
+                           mda_raw_offset + mda_raw_size - mda_size,
+                           metadatabuf + mda_size - mda_raw_offset);
+      if (err)
+       goto fail2;
+    }
+  else
+    {
+      err = grub_disk_read (disk, 0,
+                           mda_offset + mda_raw_offset,
+                           mda_raw_size,
+                           metadatabuf);
+      if (err)
+       goto fail2;
     }
-  p = q = metadatabuf + grub_le_to_cpu64 (rlocn->offset);
+  p = q = metadatabuf;
 
-  while (*q != ' ' && q < metadatabuf + mda_size)
+  while (*q != ' ' && q < metadatabuf + mda_raw_size)
     q++;
 
-  if (q == metadatabuf + mda_size)
+  if (q == metadatabuf + mda_raw_size)
     {
 #ifdef GRUB_UTIL
       grub_util_info ("error parsing metadata");
-- 
2.6.6