From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Colin Watson <cjwatson@debian.org>

Date: Sat, 25 Jul 2020 12:15:37 +0100

Subject: [PATCH] linux: Fix integer overflows in initrd size handling

These could be triggered by a crafted filesystem with very large files.

Fixes: CVE-2020-15707

Signed-off-by: Colin Watson <cjwatson@debian.org>

Reviewed-by: Jan Setje-Eilers <jan.setjeeilers@oracle.com>

---

 grub-core/loader/linux.c | 74 +++++++++++++++++++++++++++++++++++-------------

 1 file changed, 54 insertions(+), 20 deletions(-)

diff --git a/grub-core/loader/linux.c b/grub-core/loader/linux.c

index 2305281df04..951f7556fb4 100644

--- a/grub-core/loader/linux.c

+++ b/grub-core/loader/linux.c

@@ -4,6 +4,7 @@

 #include <grub/misc.h>

 #include <grub/file.h>

 #include <grub/mm.h>

+#include <grub/safemath.h>

 struct newc_head

 {

@@ -98,13 +99,13 @@ free_dir (struct dir *root)

   grub_free (root);

 }

-static grub_size_t

+static grub_err_t

 insert_dir (const char *name, struct dir **root,

-	    grub_uint8_t *ptr)

+	    grub_uint8_t *ptr, grub_size_t *size)

 {

   struct dir *cur, **head = root;

   const char *cb, *ce = name;

-  grub_size_t size = 0;

+  *size = 0;

   while (1)

     {

       for (cb = ce; *cb == '/'; cb++);

@@ -130,14 +131,22 @@ insert_dir (const char *name, struct dir **root,

 	      ptr = make_header (ptr, name, ce - name,

 				 040777, 0);

 	    }

-	  size += ALIGN_UP ((ce - (char *) name)

-			    + sizeof (struct newc_head), 4);

+	  if (grub_add (*size,

+		        ALIGN_UP ((ce - (char *) name)

+				  + sizeof (struct newc_head), 4),

+			size))

+	    {

+	      grub_error (GRUB_ERR_OUT_OF_RANGE, N_("overflow is detected"));

+	      grub_free (n->name);

+	      grub_free (n);

+	      return grub_errno;

+	    }

 	  *head = n;

 	  cur = n;

 	}

       root = &cur->next;

     }

-  return size;

+  return GRUB_ERR_NONE;

 }

 grub_err_t

@@ -174,26 +183,33 @@ grub_initrd_init (int argc, char *argv[],

 	  if (eptr)

 	    {

 	      grub_file_filter_disable_compression ();

+	      grub_size_t dir_size, name_len;

+

 	      initrd_ctx->components[i].newc_name = grub_strndup (ptr, eptr - ptr);

-	      if (!initrd_ctx->components[i].newc_name)

+	      if (!initrd_ctx->components[i].newc_name ||

+		  insert_dir (initrd_ctx->components[i].newc_name, &root, 0,

+			      &dir_size))

 		{

 		  grub_initrd_close (initrd_ctx);

 		  return grub_errno;

 		}

-	      initrd_ctx->size

-		+= ALIGN_UP (sizeof (struct newc_head)

-			    + grub_strlen (initrd_ctx->components[i].newc_name),

-			     4);

-	      initrd_ctx->size += insert_dir (initrd_ctx->components[i].newc_name,

-					      &root, 0);

+	      name_len = grub_strlen (initrd_ctx->components[i].newc_name);

+	      if (grub_add (initrd_ctx->size,

+			    ALIGN_UP (sizeof (struct newc_head) + name_len, 4),

+			    &initrd_ctx->size) ||

+		  grub_add (initrd_ctx->size, dir_size, &initrd_ctx->size))

+		goto overflow;

 	      newc = 1;

 	      fname = eptr + 1;

 	    }

 	}

       else if (newc)

 	{

-	  initrd_ctx->size += ALIGN_UP (sizeof (struct newc_head)

-					+ sizeof ("TRAILER!!!") - 1, 4);

+	  if (grub_add (initrd_ctx->size,

+			ALIGN_UP (sizeof (struct newc_head)

+				  + sizeof ("TRAILER!!!") - 1, 4),

+			&initrd_ctx->size))

+	    goto overflow;

 	  free_dir (root);

 	  root = 0;

 	  newc = 0;

@@ -208,19 +224,29 @@ grub_initrd_init (int argc, char *argv[],

       initrd_ctx->nfiles++;

       initrd_ctx->components[i].size

 	= grub_file_size (initrd_ctx->components[i].file);

-      initrd_ctx->size += initrd_ctx->components[i].size;

+      if (grub_add (initrd_ctx->size, initrd_ctx->components[i].size,

+		    &initrd_ctx->size))

+	goto overflow;

     }

   if (newc)

     {

       initrd_ctx->size = ALIGN_UP (initrd_ctx->size, 4);

-      initrd_ctx->size += ALIGN_UP (sizeof (struct newc_head)

-				    + sizeof ("TRAILER!!!") - 1, 4);

+      if (grub_add (initrd_ctx->size,

+		    ALIGN_UP (sizeof (struct newc_head)

+			      + sizeof ("TRAILER!!!") - 1, 4),

+		    &initrd_ctx->size))

+	goto overflow;

       free_dir (root);

       root = 0;

     }

   return GRUB_ERR_NONE;

+

+overflow:

+  free_dir (root);

+  grub_initrd_close (initrd_ctx);

+  return grub_error (GRUB_ERR_OUT_OF_RANGE, N_("overflow is detected"));

 }

 grub_size_t

@@ -261,8 +287,16 @@ grub_initrd_load (struct grub_linux_initrd_context *initrd_ctx,

       if (initrd_ctx->components[i].newc_name)

 	{

-	  ptr += insert_dir (initrd_ctx->components[i].newc_name,

-			     &root, ptr);

+	  grub_size_t dir_size;

+

+	  if (insert_dir (initrd_ctx->components[i].newc_name, &root, ptr,

+			  &dir_size))

+	    {

+	      free_dir (root);

+	      grub_initrd_close (initrd_ctx);

+	      return grub_errno;

+	    }

+	  ptr += dir_size;

 	  ptr = make_header (ptr, initrd_ctx->components[i].newc_name,

 			     grub_strlen (initrd_ctx->components[i].newc_name),

 			     0100777,