ext4: calculate and verify superblock checksum

Calculate and verify the superblock checksum.  Since the UUID and
block group number are embedded in each copy of the superblock, we
need only checksum the entire block.  Refactor some of the code to
eliminate open-coding of the checksum update call.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 47 insertions, 0 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 11a0a7078da7..f80c7e612829 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -122,6 +122,38 @@ static int ext4_verify_csum_type(struct super_block *sb,
         return es->s_checksum_type == EXT4_CRC32C_CHKSUM;
 }
 
+static __le32 ext4_superblock_csum(struct super_block *sb,
+                                   struct ext4_super_block *es)
+{
+        struct ext4_sb_info *sbi = EXT4_SB(sb);
+        int offset = offsetof(struct ext4_super_block, s_checksum);
+        __u32 csum;
+
+        csum = ext4_chksum(sbi, ~0, (char *)es, offset);
+
+        return cpu_to_le32(csum);
+}
+
+int ext4_superblock_csum_verify(struct super_block *sb,
+                                struct ext4_super_block *es)
+{
+        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
+                                       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+                return 1;
+
+        return es->s_checksum == ext4_superblock_csum(sb, es);
+}
+
+void ext4_superblock_csum_set(struct super_block *sb,
+                              struct ext4_super_block *es)
+{
+        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
+                EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+                return;
+
+        es->s_checksum = ext4_superblock_csum(sb, es);
+}
+
 void *ext4_kvmalloc(size_t size, gfp_t flags)
 {
         void *ret;
@@ -3057,6 +3089,20 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
                 }
         }
 
+        /* Check superblock checksum */
+        if (!ext4_superblock_csum_verify(sb, es)) {
+                ext4_msg(sb, KERN_ERR, "VFS: Found ext4 filesystem with "
+                         "invalid superblock checksum.  Run e2fsck?");
+                silent = 1;
+                goto cantfind_ext4;
+        }
+
+        /* Precompute checksum seed for all metadata */
+        if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
+                        EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+                sbi->s_csum_seed = ext4_chksum(sbi, ~0, es->s_uuid,
+                                               sizeof(es->s_uuid));
+
         /* Set defaults before we parse the mount options */
         def_mount_opts = le32_to_cpu(es->s_default_mount_opts);
         set_opt(sb, INIT_INODE_TABLE);
@@ -4059,6 +4105,7 @@ static int ext4_commit_super(struct super_block *sb, int sync)
                                 &EXT4_SB(sb)->s_freeinodes_counter));
         sb->s_dirt = 0;
         BUFFER_TRACE(sbh, "marking dirty");
+        ext4_superblock_csum_set(sb, es);
         mark_buffer_dirty(sbh);
         if (sync) {
                 error = sync_dirty_buffer(sbh);