udf: Avoid invalid LVID used on mount

udf_load_logicalvolint() loads logical volume integrity descriptors.
Since there can be multiple blocks with LVIDs, we verify the contents of
only the last (prevailing) LVID found. However if we fail to load the
last LVID (either due to IO error or because it's checksum fails to
match), we never perform the verification of validity of the LVID we are
going to use. If such LVID contains invalid data, we can hit
out-of-bounds access or similar issues. Fix the problem by verifying
each LVID we are potentially going to accept.

Reported-by: Robert Morris <rtm@csail.mit.edu>
Signed-off-by: Jan Kara <jack@suse.cz>

Author: jankara

fs/udf/super.c

@@ -1539,6 +1539,20 @@ static int udf_load_logicalvol(struct super_block *sb, sector_t block,
 	return ret;
 }
 
+static bool udf_lvid_valid(struct super_block *sb,
+			   struct logicalVolIntegrityDesc *lvid)
+{
+	u32 parts, impuselen;
+
+	parts = le32_to_cpu(lvid->numOfPartitions);
+	impuselen = le32_to_cpu(lvid->lengthOfImpUse);
+	if (parts >= sb->s_blocksize || impuselen >= sb->s_blocksize ||
+	    sizeof(struct logicalVolIntegrityDesc) + impuselen +
+	    2 * parts * sizeof(u32) > sb->s_blocksize)
+		return false;
+	return true;
+}
+
 /*
  * Find the prevailing Logical Volume Integrity Descriptor.
  */
@@ -1549,7 +1563,6 @@ static void udf_load_logicalvolint(struct super_block *sb, struct kernel_extent_
 	struct udf_sb_info *sbi = UDF_SB(sb);
 	struct logicalVolIntegrityDesc *lvid;
 	int indirections = 0;
-	u32 parts, impuselen;
 
 	while (++indirections <= UDF_MAX_LVID_NESTING) {
 		final_bh = NULL;
@@ -1571,32 +1584,27 @@ static void udf_load_logicalvolint(struct super_block *sb, struct kernel_extent_
 		if (!final_bh)
 			return;
 
-		brelse(sbi->s_lvid_bh);
-		sbi->s_lvid_bh = final_bh;
-
 		lvid = (struct logicalVolIntegrityDesc *)final_bh->b_data;
+		if (udf_lvid_valid(sb, lvid)) {
+			brelse(sbi->s_lvid_bh);
+			sbi->s_lvid_bh = final_bh;
+		} else {
+			udf_warn(sb, "Corrupted LVID (parts=%u, impuselen=%u), "
+				 "ignoring.\n",
+				 le32_to_cpu(lvid->numOfPartitions),
+				 le32_to_cpu(lvid->lengthOfImpUse));
+		}
+
 		if (lvid->nextIntegrityExt.extLength == 0)
-			goto check;
+			return;
 
 		loc = leea_to_cpu(lvid->nextIntegrityExt);
 	}
 
 	udf_warn(sb, "Too many LVID indirections (max %u), ignoring.\n",
 		UDF_MAX_LVID_NESTING);
-out_err:
 	brelse(sbi->s_lvid_bh);
 	sbi->s_lvid_bh = NULL;
-	return;
-check:
-	parts = le32_to_cpu(lvid->numOfPartitions);
-	impuselen = le32_to_cpu(lvid->lengthOfImpUse);
-	if (parts >= sb->s_blocksize || impuselen >= sb->s_blocksize ||
-	    sizeof(struct logicalVolIntegrityDesc) + impuselen +
-	    2 * parts * sizeof(u32) > sb->s_blocksize) {
-		udf_warn(sb, "Corrupted LVID (parts=%u, impuselen=%u), "
-			 "ignoring.\n", parts, impuselen);
-		goto out_err;
-	}
 }
 
 /*