1 files changed, 47 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index e2bdf93693a6..dd4ff9c87358 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -37,12 +37,14 @@
 #include <linux/quotaops.h>
 #include <linux/seq_file.h>
 #include <linux/log2.h>
+#include <linux/crc16.h>
 
 #include <asm/uaccess.h>
 
 #include "xattr.h"
 #include "acl.h"
 #include "namei.h"
+#include "group.h"
 
 static int ext4_load_journal(struct super_block *, struct ext4_super_block *,
                              unsigned long journal_devnum);
@@ -1308,6 +1310,43 @@ static int ext4_setup_super(struct super_block *sb, struct ext4_super_block *es,
         return res;
 }
 
+__le16 ext4_group_desc_csum(struct ext4_sb_info *sbi, __u32 block_group,
+                            struct ext4_group_desc *gdp)
+{
+        __u16 crc = 0;
+
+        if (sbi->s_es->s_feature_ro_compat &
+            cpu_to_le32(EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {
+                int offset = offsetof(struct ext4_group_desc, bg_checksum);
+                __le32 le_group = cpu_to_le32(block_group);
+
+                crc = crc16(~0, sbi->s_es->s_uuid, sizeof(sbi->s_es->s_uuid));
+                crc = crc16(crc, (__u8 *)&le_group, sizeof(le_group));
+                crc = crc16(crc, (__u8 *)gdp, offset);
+                offset += sizeof(gdp->bg_checksum); /* skip checksum */
+                /* for checksum of struct ext4_group_desc do the rest...*/
+                if ((sbi->s_es->s_feature_incompat &
+                     cpu_to_le32(EXT4_FEATURE_INCOMPAT_64BIT)) &&
+                    offset < le16_to_cpu(sbi->s_es->s_desc_size))
+                        crc = crc16(crc, (__u8 *)gdp + offset,
+                                    le16_to_cpu(sbi->s_es->s_desc_size) -
+                                        offset);
+        }
+
+        return cpu_to_le16(crc);
+}
+
+int ext4_group_desc_csum_verify(struct ext4_sb_info *sbi, __u32 block_group,
+                                struct ext4_group_desc *gdp)
+{
+        if ((sbi->s_es->s_feature_ro_compat &
+             cpu_to_le32(EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) &&
+            (gdp->bg_checksum != ext4_group_desc_csum(sbi, block_group, gdp)))
+                return 0;
+
+        return 1;
+}
+
 /* Called at mount-time, super-block is locked */
 static int ext4_check_descriptors (struct super_block * sb)
 {
@@ -1362,6 +1401,14 @@ static int ext4_check_descriptors (struct super_block * sb)
                                     i, inode_table);
                         return 0;
                 }
+                if (!ext4_group_desc_csum_verify(sbi, i, gdp)) {
+                        ext4_error(sb, __FUNCTION__,
+                                   "Checksum for group %d failed (%u!=%u)\n", i,
+                                   le16_to_cpu(ext4_group_desc_csum(sbi, i,
+                                                                    gdp)),
+                                   le16_to_cpu(gdp->bg_checksum));
+                        return 0;
+                }
                 first_block += EXT4_BLOCKS_PER_GROUP(sb);
                 gdp = (struct ext4_group_desc *)
                         ((__u8 *)gdp + EXT4_DESC_SIZE(sb));