ext4: Allow read/only mounts with corrupted block group checksums

If the block group checksums are corrupted, still allow the mount to
succeed, so e2fsck can have a chance to try to fix things up.  Add
code in the remount r/w path to make sure the block group checksums
are valid before allowing the filesystem to be remounted read/write.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 23 insertions, 1 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index b5479b1dff14..876e1c620365 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1626,7 +1626,8 @@ static int ext4_check_descriptors(struct super_block *sb)
                                "Checksum for group %lu failed (%u!=%u)\n",
                                i, le16_to_cpu(ext4_group_desc_csum(sbi, i,
                                gdp)), le16_to_cpu(gdp->bg_checksum));
-                        return 0;
+                        if (!(sb->s_flags & MS_RDONLY))
+                                return 0;
                 }
                 if (!flexbg_flag)
                         first_block += EXT4_BLOCKS_PER_GROUP(sb);
@@ -2961,6 +2962,7 @@ static int ext4_remount (struct super_block * sb, int * flags, char * data)
         ext4_fsblk_t n_blocks_count = 0;
         unsigned long old_sb_flags;
         struct ext4_mount_options old_opts;
+        ext4_group_t g;
         int err;
 #ifdef CONFIG_QUOTA
         int i;
@@ -3039,6 +3041,26 @@ static int ext4_remount (struct super_block * sb, int * flags, char * data)
                         }
 
                         /*
+                         * Make sure the group descriptor checksums
+                         * are sane.  If they aren't, refuse to
+                         * remount r/w.
+                         */
+                        for (g = 0; g < sbi->s_groups_count; g++) {
+                                struct ext4_group_desc *gdp =
+                                        ext4_get_group_desc(sb, g, NULL);
+
+                                if (!ext4_group_desc_csum_verify(sbi, g, gdp)) {
+                                        printk(KERN_ERR
+               "EXT4-fs: ext4_remount: "
+                "Checksum for group %lu failed (%u!=%u)\n",
+                g, le16_to_cpu(ext4_group_desc_csum(sbi, g, gdp)),
+                                               le16_to_cpu(gdp->bg_checksum));
+                                        err = -EINVAL;
+                                        goto restore_opts;
+                                }
+                        }
+
+                        /*
                          * If we have an unprocessed orphan list hanging
                          * around from a previously readonly bdev mount,
                          * require a full umount/remount for now.