[PATCH 2/4] fs/iso9660: Prevent read past the end of system use area

[Lidong Chen]

In the code, the for loop advanced the entry pointer to the
next entry before checking if the next entry is within the
system use area boundary. Another issue in the code was that
there is no check for the size of system use area. For a
corrupted system, the size of system use area can be less than
the size of SUSP entry size (5 bytes). These can cause buffer
overrun. The fixes added the checks to ensure the read is
valid and within the boundary.

Signed-off-by: Lidong Chen <lidong.chen@oracle.com>
---
 grub-core/fs/iso9660.c | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/grub-core/fs/iso9660.c b/grub-core/fs/iso9660.c
index 4f4cd6165..9170fa820 100644
--- a/grub-core/fs/iso9660.c
+++ b/grub-core/fs/iso9660.c
@@ -49,6 +49,8 @@ GRUB_MOD_LICENSE ("GPLv3+");
 #define GRUB_ISO9660_VOLDESC_PART      3
 #define GRUB_ISO9660_VOLDESC_END       255
 
+#define GRUB_ISO9660_SUSP_HEADER_SZ    5
+
 /* The head of a volume descriptor.  */
 struct grub_iso9660_voldesc
 {
@@ -272,6 +274,9 @@ grub_iso9660_susp_iterate (grub_fshelp_node_t node, 
grub_off_t off,
   if (sua_size <= 0)
     return GRUB_ERR_NONE;
 
+  if (sua_size < GRUB_ISO9660_SUSP_HEADER_SZ)
+    return grub_error (GRUB_ERR_BAD_FS, "invalid susp entry size");
+
   sua = grub_malloc (sua_size);
   if (!sua)
     return grub_errno;
@@ -281,10 +286,14 @@ grub_iso9660_susp_iterate (grub_fshelp_node_t node, 
grub_off_t off,
   if (err)
     return err;
 
-  for (entry = (struct grub_iso9660_susp_entry *) sua; (char *) entry < (char 
*) sua + sua_size - 1 && entry->len > 0;
-       entry = (struct grub_iso9660_susp_entry *)
-        ((char *) entry + entry->len))
+  entry = (struct grub_iso9660_susp_entry *) sua;
+
+  while (entry->len > 0)
     {
+      /* Ensure the entry is within System Use Area */
+      if ((char *) entry + entry->len > (sua + sua_size))
+        break;
+
       /* The last entry.  */
       if (grub_strncmp ((char *) entry->sig, "ST", 2) == 0)
        break;
@@ -300,6 +309,15 @@ grub_iso9660_susp_iterate (grub_fshelp_node_t node, 
grub_off_t off,
          off = grub_le_to_cpu32 (ce->off);
          ce_block = grub_le_to_cpu32 (ce->blk) << GRUB_ISO9660_LOG2_BLKSZ;
 
+         if (sua_size <= 0)
+           break;
+
+         if (sua_size < GRUB_ISO9660_SUSP_HEADER_SZ)
+           {
+             grub_free (sua);
+             return grub_error (GRUB_ERR_BAD_FS, "invalid CE entry size");
+           }
+
          grub_free (sua);
          sua = grub_malloc (sua_size);
          if (!sua)
@@ -319,6 +337,11 @@ grub_iso9660_susp_iterate (grub_fshelp_node_t node, 
grub_off_t off,
          grub_free (sua);
          return 0;
        }
+
+      entry = (struct grub_iso9660_susp_entry *) ((char *) entry + entry->len);
+
+      if (((sua + sua_size) - (char *) entry) < GRUB_ISO9660_SUSP_HEADER_SZ)
+        break;
     }
 
   grub_free (sua);
@@ -574,7 +597,7 @@ susp_iterate_dir (struct grub_iso9660_susp_entry *entry,
          char *old;
          grub_size_t sz;
 
-         csize = entry->len - 5;
+         csize = entry->len - GRUB_ISO9660_SUSP_HEADER_SZ;
          old = ctx->filename;
          if (ctx->filename_alloc)
            {
-- 
2.35.1