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mke2fs: prevent creation of unmountable ext4 with large flex_bg count 

In mke2fs command, if flex_bg count is too large to filesystem blocks
count, unmountable ext4 which has the out of filesystem block offset
is created (Case1).  Moreover this large flex_bg count causes an
unintentional metadata layout (bmap-imap-itable-bmap-imap-itable .. in
block group) (Case2).

To fix these issues and keep healthy flex_bg layout, disallow creating
ext4 with obviously large flex_bg count to filesystem blocks count.

Steps to reproduce:
(Case1)
1.
    # mke2fs -t ext4 -b 4096 -O ^resize_inode -G $((2**20)) DEV 2130483

2.
    # mount -t ext4 DEV MP
    mount: wrong fs type, bad option, bad superblock on /dev/sdb4,
           missing codepage or helper program, or other error
           In some cases useful info is found in syslog - try
           dmesg | tail  or so

3.
    # dumpe2fs DEV
    ...
    Block count:              2130483
    ...
    Flex block group size:    1048576
    ...
    Group 65: (Blocks 2129920-2130482) [INODE_UNINIT]
      Checksum 0x4cb3, unused inodes 8080
      Block bitmap at 67 (bg #0 + 67), Inode bitmap at 1048643 (bg #32 + 67)
      Inode table at 2129979-2130483 (+59)
                             ^^^^^^^  2130483 is out of FS!
      65535 free blocks, 8080 free inodes, 0 directories, 8080 unused inodes
      Free blocks:
      Free inodes: 525201-533280

(Case2)
1.
    # mke2fs -t ext4 -G 2147483648 DEV 3145728

2.
    # debugfs -R stats DEV
    ...
    Block count:              786432
    ...
    Flex block group size:    2147483648
    ...
     Group  0: block bitmap at 193, inode bitmap at 194, inode table at 195
    ...
     Group  1: block bitmap at 707, inode bitmap at 708, inode table at 709
    ...
     Group  2: block bitmap at 1221, inode bitmap at 1222, inode table at 1223
    ...

Signed-off-by: Akira Fujita <a-fujita@rs.jp.nec.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
maint-test
Akira Fujita 2014-07-05 22:42:36 -04:00 committed by Theodore Ts'o
parent d0de4c9540
commit d988201ef9
1 changed files with 24 additions and 0 deletions
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24
lib/ext2fs/initialize.c
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@ -91,8 +91,10 @@ errcode_t ext2fs_initialize(const char *name, int flags,
unsigned int rem;
unsigned int overhead = 0;
unsigned int ipg;
unsigned int flexbg_size;
dgrp_t i;
blk64_t free_blocks;
blk64_t flexbg_overhead;
blk_t numblocks;
int rsv_gdt;
int csum_flag;
@ -418,6 +420,28 @@ ipg_retry:
goto retry;
}
/*
* Calculate the flex_bg related metadata blocks count.
* It includes the boot block, the super block,
* the block group descriptors, the reserved gdt blocks,
* the block bitmaps, the inode bitmaps and the inode tables.
* This is a simple check, so that the backup superblock and
* other feature related blocks are not considered.
*/
flexbg_size = 1 << fs->super->s_log_groups_per_flex;
flexbg_overhead = super->s_first_data_block + 1 +
fs->desc_blocks + super->s_reserved_gdt_blocks +
(__u64)flexbg_size * (2 + fs->inode_blocks_per_group);
/*
* Disallow creating ext4 which breaks flex_bg metadata layout
* obviously.
*/
if (flexbg_overhead > ext2fs_blocks_count(fs->super)) {
retval = EXT2_ET_INVALID_ARGUMENT;
goto cleanup;
}
/*
* At this point we know how big the filesystem will be. So
* we can do any and all allocations that depend on the block