ext4: validate that metadata blocks do not overlap superblock

commit 829fa70dddadf9dd041d62b82cd7cea63943899d upstream.

A number of fuzzing failures seem to be caused by allocation bitmaps
or other metadata blocks being pointed at the superblock.

This can cause kernel BUG or WARNings once the superblock is
overwritten, so validate the group descriptor blocks to make sure this
doesn't happen.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 55e88c8..7266a2e 100644 (file)
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2097,6 +2097,7 @@ int ext4_group_desc_csum_verify(struct ext4_sb_info *sbi, __u32 block_group,
 
 /* Called at mount-time, super-block is locked */
 static int ext4_check_descriptors(struct super_block *sb,
 
 /* Called at mount-time, super-block is locked */
 static int ext4_check_descriptors(struct super_block *sb,

+                                 ext4_fsblk_t sb_block,

                                  ext4_group_t *first_not_zeroed)
 {
        struct ext4_sb_info *sbi = EXT4_SB(sb);
                                  ext4_group_t *first_not_zeroed)
 {
        struct ext4_sb_info *sbi = EXT4_SB(sb);


@@ -2127,6 +2128,11 @@ static int ext4_check_descriptors(struct super_block *sb,
                        grp = i;
 
                block_bitmap = ext4_block_bitmap(sb, gdp);
                        grp = i;
 
                block_bitmap = ext4_block_bitmap(sb, gdp);

+               if (block_bitmap == sb_block) {
+                       ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
+                                "Block bitmap for group %u overlaps "
+                                "superblock", i);
+               }

                if (block_bitmap < first_block || block_bitmap > last_block) {
                        ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
                               "Block bitmap for group %u not in group "
                if (block_bitmap < first_block || block_bitmap > last_block) {
                        ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
                               "Block bitmap for group %u not in group "


@@ -2134,6 +2140,11 @@ static int ext4_check_descriptors(struct super_block *sb,
                        return 0;
                }
                inode_bitmap = ext4_inode_bitmap(sb, gdp);
                        return 0;
                }
                inode_bitmap = ext4_inode_bitmap(sb, gdp);

+               if (inode_bitmap == sb_block) {
+                       ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
+                                "Inode bitmap for group %u overlaps "
+                                "superblock", i);
+               }

                if (inode_bitmap < first_block || inode_bitmap > last_block) {
                        ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
                               "Inode bitmap for group %u not in group "
                if (inode_bitmap < first_block || inode_bitmap > last_block) {
                        ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
                               "Inode bitmap for group %u not in group "


@@ -2141,6 +2152,11 @@ static int ext4_check_descriptors(struct super_block *sb,
                        return 0;
                }
                inode_table = ext4_inode_table(sb, gdp);
                        return 0;
                }
                inode_table = ext4_inode_table(sb, gdp);

+               if (inode_table == sb_block) {
+                       ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
+                                "Inode table for group %u overlaps "
+                                "superblock", i);
+               }

                if (inode_table < first_block ||
                    inode_table + sbi->s_itb_per_group - 1 > last_block) {
                        ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
                if (inode_table < first_block ||
                    inode_table + sbi->s_itb_per_group - 1 > last_block) {
                        ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "


@@ -3674,7 +3690,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
                        goto failed_mount2;
                }
        }
                        goto failed_mount2;
                }
        }

-       if (!ext4_check_descriptors(sb, &first_not_zeroed)) {
+       if (!ext4_check_descriptors(sb, logical_sb_block, &first_not_zeroed)) {

                ext4_msg(sb, KERN_ERR, "group descriptors corrupted!");
                goto failed_mount2;
        }
                ext4_msg(sb, KERN_ERR, "group descriptors corrupted!");
                goto failed_mount2;
        }