ext4: add checksums to the MMP block

Compute and verify a checksum for the MMP block.

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

2 files changed, 42 insertions, 5 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 84e76bb96070..0ee9669394f5 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2413,6 +2413,9 @@ extern int ext4_bio_write_page(struct ext4_io_submit *io,
 
 /* mmp.c */
 extern int ext4_multi_mount_protect(struct super_block *, ext4_fsblk_t);
+extern void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp);
+extern int ext4_mmp_csum_verify(struct super_block *sb,
+                                struct mmp_struct *mmp);
 
 /* BH_Uninit flag: blocks are allocated but uninitialized on disk */
 enum ext4_state_bits {
diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index ed6548d89165..f99a1311e847 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c
@@ -6,12 +6,45 @@
 
 #include "ext4.h"
 
+/* Checksumming functions */
+static __u32 ext4_mmp_csum(struct super_block *sb, struct mmp_struct *mmp)
+{
+        struct ext4_sb_info *sbi = EXT4_SB(sb);
+        int offset = offsetof(struct mmp_struct, mmp_checksum);
+        __u32 csum;
+
+        csum = ext4_chksum(sbi, sbi->s_csum_seed, (char *)mmp, offset);
+
+        return cpu_to_le32(csum);
+}
+
+int ext4_mmp_csum_verify(struct super_block *sb, struct mmp_struct *mmp)
+{
+        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
+                                       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+                return 1;
+
+        return mmp->mmp_checksum == ext4_mmp_csum(sb, mmp);
+}
+
+void ext4_mmp_csum_set(struct super_block *sb, struct mmp_struct *mmp)
+{
+        if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
+                                       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+                return;
+
+        mmp->mmp_checksum = ext4_mmp_csum(sb, mmp);
+}
+
 /*
  * Write the MMP block using WRITE_SYNC to try to get the block on-disk
  * faster.
  */
-static int write_mmp_block(struct buffer_head *bh)
+static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
 {
+        struct mmp_struct *mmp = (struct mmp_struct *)(bh->b_data);
+
+        ext4_mmp_csum_set(sb, mmp);
         mark_buffer_dirty(bh);
         lock_buffer(bh);
         bh->b_end_io = end_buffer_write_sync;
@@ -59,7 +92,8 @@ static int read_mmp_block(struct super_block *sb, struct buffer_head **bh,
         }
 
         mmp = (struct mmp_struct *)((*bh)->b_data);
-        if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC)
+        if (le32_to_cpu(mmp->mmp_magic) != EXT4_MMP_MAGIC ||
+            !ext4_mmp_csum_verify(sb, mmp))
                 return -EINVAL;
 
         return 0;
@@ -120,7 +154,7 @@ static int kmmpd(void *data)
                 mmp->mmp_time = cpu_to_le64(get_seconds());
                 last_update_time = jiffies;
 
-                retval = write_mmp_block(bh);
+                retval = write_mmp_block(sb, bh);
                 /*
                  * Don't spew too many error messages. Print one every
                  * (s_mmp_update_interval * 60) seconds.
@@ -200,7 +234,7 @@ static int kmmpd(void *data)
         mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
         mmp->mmp_time = cpu_to_le64(get_seconds());
 
-        retval = write_mmp_block(bh);
+        retval = write_mmp_block(sb, bh);
 
 failed:
         kfree(data);
@@ -299,7 +333,7 @@ skip:
         seq = mmp_new_seq();
         mmp->mmp_seq = cpu_to_le32(seq);
 
-        retval = write_mmp_block(bh);
+        retval = write_mmp_block(sb, bh);
         if (retval)
                 goto failed;